CHAPTER 20 DIAGNOSTIC IMAGING OF THE SELLAR REGION
Principles and Practice of Endocrinology and Metabolism
CHAPTER 20 DIAGNOSTIC IMAGING OF THE SELLAR REGION
ERIC BOUREKAS, MARY OEHLER, AND DONALD CHAKERES
Advantages and Disadvantages of Imaging Techniques
Normal Imaging Anatomy
Computed Tomographic Imaging
Magnetic Resonance Imaging
Optic Chiasm and Hypothalamic Gliomas
Sellar and Parasellar Meningioma
Schwannomas and Neurofibromas
Sphenoid Sinus Disease
Primary Hypothyroidism and Nelson Syndrome
Radiographic imaging of the sella and hypothalamic region is important in the overall evaluation of many patients with endocrine and metabolic disorders. Often, imaging is crucial, because different pathology in this region may present with similar clinical findings. Imaging can help identify a number of diagnostic entities based on anatomicopathologic characteristics. For example, in patients with hypopituitarism, one can often pinpoint the etiology more precisely, determining, for example, whether it is secondary to congenital absence of the gland, septo-optic dysplasia, transection of the pituitary stalk, a large pituitary mass, a suprasellar arachnoid cyst, a hypothalamic glioma, or an eosinophilic granuloma. In addition, in those patients who have known endocrine disorders such as acromegaly, imaging characterizes other important anatomic aspects of the pathology, such as the size of the mass and possible involvement of the optic chiasm or cavernous sinuses. Imaging of the venous drainage of the pituitary fossa is also used to allow for venous sinus sampling of blood for hormone analysis. Finally, imaging helps direct interventional procedures (i.e., surgery, radiotherapy) in the sellar region and plays a role in postoperative evaluation.
In this chapter, the various imaging modalities and their advantages and disadvantages are discussed in terms of their specific applications. A review is provided of the normal imaging anatomy and of the more commonly encountered pathologic entities, including normal variations, congenital anomalies, inflammations, neoplasms, trauma, and vascular disorders. The focus is primarily on disorders associated with endocrine malfunction.
ADVANTAGES AND DISADVANTAGES OF IMAGING TECHNIQUES
Traditionally, the first imaging examination in the evaluation of the pituitary-sellar region was a skull radiograph series.1 Plain radiographs offer the advantage of being noninvasive and inexpensive; they yield a certain amount of limited information about the adjacent bony structures (Fig. 20-1). However, potentially important secondary soft-tissue changes can only be inferred, although soft-tissue calcifications can be seen. Thus, in general, routine radiographs provide only minimal information related to the sella, and hence are generally not obtained.
FIGURE 20-1. Lateral radiograph of sella. Labeled structures include planum sphenoidale (curved solid white arrows), tuberculum sella (short black arrow), lamina terminalis (open white arrow), sphenoid sinus (black arrowheads), anterior clinoid (long thin black arrow), and posterior clinoid (open curved white arrow). This patient has a relatively well-pneumatized sphenoid sinus. The chiasmatic sulcus is not well marginated.
Computed tomography (CT) was the first imaging modality to directly visualize the pituitary gland, hypothalamus, and optic chiasm.2 The bony structures in this region can be well evaluated with CT (Fig. 20-2). It is more sensitive than either plain radiographs or magnetic resonance imaging (MRI) in the detection of calcifications within soft tissues. However, intravenous contrast agents frequently are necessary to improve the image contrast and to enhance the vasculature, and CT involves radiation exposure.
FIGURE 20-2. Normal sellar and suprasellar CT. A, Coronal CT scan obtained with contrast enhancement through the anterior third ventricle (short curved solid white arrow), supraclinoid carotid artery (thick black arrow), calcified cavernous carotid artery (long curved solid white arrow), pituitary gland (open white arrow), anterior clinoid (small black arrowhead), cavernous sinus (long white arrow), incidental fat in the cavernous sinus (large black arrowhead), and sphenoid sinus (white arrowhead). B, Axial CT scan made with contrast enhancement through the suprasellar cistern. The labeled structures include anterior clinoids (small black arrowhead), posterior clinoids (curved solid white arrow), optic canal (curved open white arrow), pneumatized planum sphenoidale (large black arrowhead), pituitary stalk (long thin black arrow), and supraclinoid carotid artery (short black arrow).
A major disadvantage of CT is that soft-tissue characterization is less than ideal. Artifacts from beam hardening, related to the dense bone in the skull base, obscure soft-tissue detail. Additionally, on direct coronal imaging, there often are artifacts that are due to metallic dental fillings. Intravenous contrast is used to improve soft-tissue contrast and highlight the vasculature, but the contrast agent may cause life-threatening reactions.
MRI is the most important single overall imaging modality for the sellar region because it is effective in simultaneously characterizing the soft tissues, cerebrospinal fluid (CSF) spaces, and blood vessels (Fig. 20-3).3 It is an extremely flexible imaging modality for which contrast can be extensively manipulated. The images may be acquired using a number of different techniques, each of which has specific advantages. For example, MRI (as magnetic resonance angiography [MRA]) can substitute for routine catheter angiography in most situations.
FIGURE 20-3. Normal sellar and suprasellar MRI. A, Sagittal contrast-enhanced T1-weighted 3D gradient echo image. Labeled structures include the pituitary gland (PG), pituitary stalk (PS), optic chiasm (OC), corpus callosum (CC), septal vein (SV), inferior sagittal sinus (ISS), massus intermedius (MI), anterior cerebral artery (AC), anterior third ventricle (AAT), brainstem (BS), cerebral aqueduct (CA), and mammillary body (MB). B, Coronal contrast-enhanced T1-weighted image with angiographic technique. Labeled structures include the cavernous carotid artery (small black arrowhead), supraclinoid carotid artery (short black arrow), pituitary stalk (short white arrow), optic chiasm (long black arrow), infundibular recess of the third ventricle (curved solid white arrow), sphenoid sinus (open white arrow), cavernous sinus (curved open white arrow), and pituitary gland (large black arrowheads). C, Axial 3D gradient echo contrast-enhanced T1-weighted pituitary fossa. Labeled structures include the cavernous carotid artery (CA), sphenoid sinus (SS), cavernous sinus (CS), basilar artery (BA), third cranial nerve (3CN), superior orbital fissure (SOF), brainstem (BS), and pituitary gland (PG). D, Axial 3D gradient echo contrast-enhanced T1-weighted suprasellar cistern. Labeled structures include supraclinoid carotid artery (CA), suprasellar cistern (SSC), pituitary stalk (PS), basilar artery (BA), optic nerve (ON), rectus gyrus (RG), and brainstem (BS). E, Axial 3D gradient echo contrast-enhanced T1-weighted hypothalamus optic complex. Labeled structures include anterior cerebral artery (ACA), mammillary bodies (MB), anterior third ventricle (ATV), interpeduncular cistern (IPC), optic tract (OT), hypothalamus (HT), cerebral aqueduct (CA), and midbrain (MB). F, Axial spin-echo non–contrast-enhanced T1-weighted anterior posterior pituitary. Labeled structures include anterior pituitary (white arrow) and posterior pituitary (black arrow).
Although not hampered to the same extent as CT by artifacts, some magnetic susceptibility artifacts may be related to bone and air interfaces and to dental fillings; these are not as significant a problem with MRI as with CT. Moreover, MRI allows multiplanar acquisitions more readily than CT. There is no ionizing radiation with MRI, and the contrast agents are associated with far fewer serious reactions. Because of these advantages, MRI has become the method of choice for the evaluation of the pituitary gland and adjacent soft tissues, unless there is specific interest in the bone or in soft-tissue calcifications.
With precautions, the risks associated with MRI are low. Contraindications to MRI include cardiac pacemaker, a cerebral spring aneurysm clip, a metallic foreign body near a vital structure (e.g., within the eye, the spinal canal, or near a major blood vessel), neural stimulators, and some medical implants. For these patients, CT remains a possible alternative.
Cerebral angiography is still an important imaging technique and remains the gold standard for details of vasculature.4 It is the examination of choice for the evaluation of aneurysms of the sellar/parasellar region and in the evaluation of profuse bleeding during or after transsphenoidal surgery, which may be secondary to injury of the sphenopalatine arteries or the internal carotids.5 Inferior petrosal venous sinus angiography and blood sampling can also be helpful.6 The main disadvantage of angiography is the risk of serious complications. In general, although the incidence of complications is low, the results can be catastrophic (infarcts and vascular occlusions). Even venous studies may have serious complications, such as brainstem infarction. The procedure is uncomfortable or painful for the patient and is associated with radiation exposure and potential contrast complications.
NORMAL IMAGING ANATOMY
An evaluation of subtle changes of the bony architecture of the sella is not of great clinical use because there are many normal variations in the size, shape, and cortical margins of the sella. In part, this is due to differences in the configuration of the sphenoid bone and sphenoid sinus. It is important to realize that variations in the shape of the sella do not always reflect the pathology of the adjacent structures.
The sella is usually evaluated with lateral and posteroanterior plain radiographs (tomography has been largely replaced by CT). On the lateral projection, the sella turcica is a È-shaped structure that is seen as a crisp, dense cortical bone margin (see Fig. 20-1). Those segments of the sella that are outlined by the underlying air spaces of the sinuses exhibit a thin cortical margin, which is referred to as the lamina dura. If the sinus is opacified or not pneumatized and filled with bone marrow, the sellar margin is thicker.
The planum sphenoidale is a flat, thin bone that forms the roof of the anterosuperior sphenoid sinus and extends posteriorly to terminate in the anterior clinoid processes. Between the anterior clinoid processes, the planum sphenoidale ends at a small arc-shaped ridge of bone called the limbus; this forms the anterior margin of a small bony depression called the chiasmatic sulcus (which conforms to the optic chiasm and nerves). This concavity is where the optic chiasm divides into the optic nerves. The lateral margins of the chiasmatic depression extend into the optic canals that, in turn, extend anteriorly and laterally. Superior to the optic canals are the anterior clinoids, which are visible on lateral radiograph. The inferoposterior margin of the chiasmatic sulcus is the tuberculum sella, which forms the most anterior and superior margin of the sella turcica (hypophyseal fossa). The diaphragma sellae is the superior dural covering of the sella that extends from the tuberculum sella to the posterior clinoids. It cannot be seen on plain radiographs, but marks the true roof of the sella turcica. Usually, the floor of the sella is not perfectly hemicircular in configuration, but is more oval in shape. The normal range of dimensions of the bony sella from anterior to posterior on lateral radiograph is 5 to 16 mm, with a mean of 10.6 mm. The normal range of dimensions in depth is 4 to 12 mm, with a mean of 8.1 mm.7
The anteroposterior projection of the sella usually is less informative than the lateral, but it may be useful in defining the lateral margins of the sphenoid sinus and the floor of the sella. The floor of the sella frequently bows inferiorly slightly. Septations of the sphenoid sinus are frequently seen and may account for variations in the shape of the sella and pituitary gland.
COMPUTED TOMOGRAPHIC IMAGING
On CT, bone and calcified structures have a high density (similar to that seen in plain radiographs), whereas the air spaces are of low density. The CSF spaces are of intermediate density, with the fat structures (such as periorbital fat) being lower in density than the CSF. The brain and pituitary gland usually have a slightly higher density than the CSF. With the use of intravenous contrast agents, the blood vessels, cavernous sinus, pituitary gland, and pituitary stalk all enhance intensely, thus increasing their apparent density (see Fig. 20-2). This helps define the pituitary gland and the cranial nerves in the cavernous sinus. Rarely, intrathecal contrast is used for the evaluation of a CSF fistula.
In general, contrast-enhanced direct coronal CT images of the sella are the most informative, although axial sections are easier for patient positioning. If one is not able to perform direct coronal imaging, computer reconstructions of axial images into sagittal and coronal sections can be obtained, although their detail is limited. On coronal CT, the bony sella is seen as a flat to minimally concave structure with the sphenoid sinus directly inferior (see Fig. 20-2A). The lateral walls of the sella are formed by the cavernous sinuses, which are visualized on enhanced CT as contrast-filled structures bounded laterally by dura. The individual cranial nerves (oculomotor, abducens, and trochlear) can be seen in the cavernous sinus. Meckel cave, which is a CSF space extending from the posterior fossa, contains the fifth cranial nerve. The dural margins of the cave enhance, while the CSF spaces are seen as low-density, vertical, oval cavities.
The lateral margins of the pituitary gland, which presents as an oval-shaped soft-tissue structure, may be difficult to differentiate from those of the cavernous sinus. The pituitary gland usually has a flat superior margin; however, it is common for adolescents and menstruation-aged women to have a slightly convex upward superior margin. This finding can also be seen in small tumors and is less common in men. The infundibulum or pituitary stalk is seen as a thin, usually midline tubular structure, extending inferiorly from the median eminence of the arc-shaped hypothalamus to insert on the superior margin of the pituitary gland, usually in the anterior third. Both the pituitary gland and the infundibulum enhance with intravenous contrast; this is partially due to the portal venous plexus and partially due to the lack of a blood–brain barrier. Directly superior to the infundibulum, in the anterior third of the sella turcica, is the optic chiasm, which is oriented horizontally across the top of the sella. The middle portion of the chiasm is rectangular in shape. Farther anteriorly, the chiasm is more figure-8 shaped as it divides into the individual optic nerves.
Axial CT images of the sella demonstrate the air-filled sphenoid inferiorly. Asymmetry of the floor is common. The carotid arteries, which are frequently calcified in elderly patients (see Fig. 20-2A), are seen lateral to the gland in the cavernous sinus. The cavernous sinuses form the lateral flat margins adjacent to the temporal lobes. Medially, the margins between the cavernous sinus and normal pituitary may not be clear. Incidental rests of fat are frequently seen in the cavernous sinus and should not be confused with air. The pituitary gland has a circular configuration, and the suprasellar cistern has a five-pointed-star configuration. Centrally, the pituitary stalk should be visible. The anterior and posterior clinoids are also well demonstrated on axial images (see Fig. 20-2B).
MAGNETIC RESONANCE IMAGING
MRI is the examination of choice in the evaluation of the sella and parasellar regions. Unlike CT and plain radiographs, MRI does not use ionizing radiation to generate images; they are generated based on the intrinsic magnetic properties of hydrogen atoms. Respective parameters include proton density, relaxation times (T1 and T2), magnetic susceptibility, and motion. Importantly, only hydrogen atoms are detected with MRI. Regions of cortical bone or air have no signal (signal voids). The image contrast with MRI is plastic; thus, the tissues can have almost any type of signal. With routine, spin-echo, T1-weighted images, tissues with high triglyceride fat content (orbital fat, fatty bone marrow) have bright or high signal intensity. With T1-weighted images, the CSF has a low signal intensity, whereas the brain has an intermediate signal intensity. T2-weighted images demonstrate low signal intensity for fatty structures, intermediate signal intensity for the brain, and high signal intensity for tissues with high water content (e.g., CSF, cystic masses). Motion also has an imaging impact: The signal of moving atoms can have high, low, or misregistered signal intensities, depending on the type of motion and the pulse sequence.
On MRI (see Fig. 20-3), the bony portions of the sella lack signal, except for areas of fatty marrow that have a high signal intensity on T1-weighted images. The normal pituitary gland varies in size with age, growing linearly in the first years of life and developing physiologic hypertrophy at adolescence.8 In fact, the gland tends to decrease in height and increase in width and anteroposterior dimension with age.9 In adult patients younger than 50 years of age, the average height of the pituitary gland is 5.7 ± 1.4 mm, and the average length is 10.8 ± 1.2 mm.10 In newborns younger than 6 weeks of age, the superior margin of the pituitary is usually concave, with an overall globular configuration.9 In infants between the ages of 6 weeks and 2 years of age, the superior margin is convex in 46% and flat in 43%.9 The superior margin is generally flat in adults, but in 56% of menstruating women, it may be convex.8 In newborns younger than 6 weeks of age, both the anterior and posterior lobes of the pituitary are of high signal, whereas in infants 6 weeks to 2 years of age, the anterior lobe is of low signal in 52% and intermediate signal in 43%, and the posterior pituitary is of intermediate signal in 55% and of high signal in 37%.9 In adults, the normal gland is isointense with white matter, while the posterior pituitary or neurohypophysis is usually of higher signal intensity on T1-weighted images11 (see Fig. 20-3F). This is usually seen best on sagittal images as a bright spot posterior to the adenohypophysis of the gland, usually in the posterior one-third of the sella.
There has been much speculation about the cause of the high signal intensity within the posterior pituitary gland. It is probably related to neurosecretory granules. When the gland is ectopic, this bright spot is also seen proximally along the pituitary stalk, suggesting an accumulation of these substances in the hypothalamus.11 The normal infundibulum is 3.5-mm thick near its origin from the hypothalamus and 2.8-mm thick at its midpoint.12 On sagittal images, the stalk can be seen oriented slightly obliquely and inserting on the anterior one-third of the pituitary gland (see Fig. 20-3A). On coronal images, the stalk is usually midline and is seen extending from the hypothalamus to the upper margin of the pituitary (see Fig. 20-3B). With gadolinium enhancement, the pituitary gland and infundibulum enhance brightly because there is no normal blood–brain barrier in this region (see Fig. 20-3C and D). There is a characteristic enhancement pattern when one performs dynamic imaging with contrast flowing through the pituitary portal system. The enhancement starts in the infundibulum, proceeds to the central gland, and then spreads to involve the more lateral parts of the gland.13 Dynamic gradient echo MRI has been shown to be superior to conventional contrast-enhanced spin-echo imaging in delineating the margins and extent of tumor.14
The optic chiasm and the hypothalamus are intimately associated and cannot be easily separated on axial images (see Fig. 20-3E). On coronal images (see Fig. 20-3B), the pituitary gland, infundibulum, and optic chiasm have a configuration similar to that seen on CT. On most spin-echo MRIs, the cavernous sinus contains tubular areas of low signal intensity related to flowing blood in the cavernous internal carotid arteries (see Fig. 20-3F). The signal can be high with some sequences. The most common pulse sequence is the time-of-flight MRA technique. With gadolinium enhancement, the remainder of the cavernous sinus enhances (except for the cranial nerves).
The sella may not be completely filled with tissue. When the sella is partially filled with CSF in the suprasellar cistern, it is referred to as an empty sella (Fig. 20-4). A partially empty sella is a common incidental finding and usually should be considered a normal variation in anatomy. The empty sella may be related to incomplete formation of the diaphragma sella, allowing CSF into the pituitary fossa (see Chap. 11). A partially empty sella can be seen in association with pseudotumor cerebri, hydrocephalus, previous pituitary surgery, or a previous pituitary mass that has shrunk. It can also be seen after irradiation, after trauma, or as sequela of apoplexy. Occasionally, an empty sella is associated with a CSF leak or fistula. The term empty sella syndrome has been used to describe a variable clinical constellation of findings, such as headache, endocrine dysfunction, and visual disturbances, which are seen in association with a partially empty sella.15
FIGURE 20-4. Empty sella. A, Sagittal T1-weighted non–contrast-enhanced image. Note that the pituitary stalk (small black arrowhead) extends all of the way to the floor of the sella (thick black arrow). The pituitary gland is very thin and not well marginated. In this case, the clivus (large black arrowhead) has a large amount of fat generating a high signal intensity region. The other normal structures include the optic chiasm (curved white arrow) and sphenoid sinus (open white arrowhead).
B, Coronal contrast-enhanced T1-weighted image. The pituitary stalk (curved white arrow) is seen extending all of the way to the floor of the sella. The gland is seen as a thin, “crescent-shaped” structure (thick black arrow) at the base of the sella. Other labeled structures include the hypothalamus and optic chiasm (white straight arrows) and the anterior third ventricle (open white arrow).
With an empty sella, the sellar bony margins may be expanded, forming an oval or J shape on plain radiograph or CT. It is often of normal size. The CSF spaces extend into the sella; the pituitary gland may be normal, small, or large in size. The optic nerve, optic chiasm, and optic tracts may herniate into the empty sella. The main finding is visualization of the pituitary stalk extending into the fossa, which is the best way to distinguish an empty sella from a cystic mass.
The pituitary gland can be congenitally hypoplastic. Many of these patients present with a combination of endocrine deficiencies in childhood. Plain radiographs of the sella demonstrate a small sella turcica, which may measure only a few millimeters in dimension. The presence of a small bony cavity is a sign that the pituitary gland never developed to a normal size rather than an indication of some type of destructive process. Although CT and MRI confirm that the pituitary gland is small, the hypothalamus and other adjacent structures usually appear intact.
ECTOPIC POSTERIOR PITUITARY GLAND
An ectopic posterior pituitary gland is a relatively common etiology for hypopituitarism and growth hormone (GH) disturbances in young patients.16 On plain radiograph and CT, the pituitary fossa may be small or normal in size, with an ectopically placed pituitary gland. The pituitary gland itself may be hypoplastic or normal in appearance. Because CT and plain radiographs cannot differentiate the anterior and posterior lobes of the pituitary gland or demonstrate the nodule adjacent to the hypothalamus, there is really no role for these procedures in the evaluation of an ectopic posterior pituitary.
With T1-weighted MRI, the normal round or ovoid bright spot in the posterior sella, representing the posterior pituitary gland, is not seen. The ectopic posterior pituitary tissue is usually located in the region of the median eminence—the insertion of the infundibulum to the hypothalamus. Nevertheless, the posterior pituitary gland maintains its characteristic signal properties, appearing as a small, high signal nodule protruding from the undersurface of the hypothalamus on T1-weighted images (Fig. 20-5). This type of abnormality of the hypothalamus has been described in other entities, including pituitary dwarfism and traumatic transection of the infundibulum, and as a normal variant in asymptomatic patients.16,17 and 18
FIGURE 20-5. Ectopic posterior pituitary gland. A, Sagittal unenhanced T1-weighted image through the midline. Note the high signal “bright spot” of the ectopic posterior pituitary (long straight white arrow) at the junction of the posterior margin of the optic chiasm and hypothalamus. The sella (curved white arrow) is essentially empty, and the anterior pituitary and infundibulum are not well seen. B, Coronal contrast-enhanced T1-weighted image through the optic chiasm, hypothalamus, and the ectopic posterior pituitary (long white arrow). The infundibulum is not well seen, and the other adjacent structures appear normal.
RATHKE CLEFT CYST
Rathke cleft cysts are congenital variations derived from the embryologic precursors of the anterior lobe of the pituitary. The cysts have an epithelial lining and are rarely symptomatic. They may be seen incidentally and can mimic pituitary tumors. They usually occur in the midline of the anterior or superior sella. On plain radiographs of the skull, the sella is usually normal in appearance, although large Rathke cleft cysts can expand the sella. Rarely, calcifications may be seen.
On CT, the sella may be normal or slightly expanded. The cyst can usually be seen as an area of lower attenuation that is similar in signal intensity to CSF. Smaller cysts may be difficult to differentiate from small cystic tumors, and larger cysts may be confused with craniopharyngiomas. These lesions infrequently affect the cavernous sinus or optic chiasm. On MRI, Rathke cleft cysts are usually seen as small cysts displacing the normal enhancing gland. The cysts are usually isointense with CSF on all pulse sequences. Occasionally, they may have a more unusual signal that is due to hemorrhaging.
Encephaloceles are defects in the skull and dura that may be associated with herniation of the brain or meninges. Encephaloceles can be congenital or acquired. When congenital, there is an anomaly in the midline structures, resulting in a bony defect in the anterior cranial fossa, the superior nose, and the sella; this is a rare anomaly that is more common in the Asian population. An encephalocele may be associated with facial deformities as well.
On plain radiographs, the defect in the anterior cranial fossa and sella may be noted, but it often is small. On CT, the bony defect can usually be seen, and the brain can be observed to herniate into the sella. The findings on MRI are similar, but the detail of the brain is better seen, whereas the bony defect is less well seen.
Brain herniation and anomalous vessels must be distinguished from other abnormalities, such as nasal polyps or masses, because inadvertent biopsy of an encephalocele that is mistaken for a nasal mass can be catastrophic.
SUPRASELLAR ARACHNOID CYSTS
Suprasellar arachnoid cysts are parenchymal in origin and are caused by sequestered remnants of the arachnoid membrane. They can cause endocrine dysfunction, most commonly precocious puberty. On CT, these cysts may be seen to distort the chiasm, the floor of the sella, or the clinoids. They may cause hydrocephalus by compressing the third ventricle superiorly (Fig. 20-6). On plain radiographs, in skeletally immature patients, the sutures of the skull may be widened if hydrocephalus is present. The sella may also be expanded, and there may be dysplasia of the clinoid processes with remodeling but no destruction. These bony findings are also seen on CT, but additionally, the cyst is visualized as a low-density structure with an attenuation similar to CSF. When present, hydrocephalus is noted by the presence of ventriculomegaly. It may be difficult to see the cyst as a separate structure when there is severe hydrocephalus (see Fig. 20-6A); thus, it is important to look for the membranous walls of the cyst, which may invert into the third ventricle.
FIGURE 20-6. Suprasellar arachnoid cyst. A, Axial non– contrast-enhanced CT image of a young child with precocious puberty. The temporal horns are markedly dilated (thin black arrows). The suprasellar cistern is expanded (thick white arrows), but the cyst walls are not visible. B, Sagittal non– contrast-enhanced T1-weighted magnetic resonance image through the midline. The sella is small, and the clinoids are somewhat deformed (short black arrows). There is a large cere-brospinal fluid space filling the suprasellar region (straight white arrows). The third ventricle is inverted, and the brainstem is displaced posteriorly. The cyst extends all of the way to the foramen of Monro (small black arrowhead) and columns of the fornix (large black arrowhead). C, Axial contrast-enhanced T1-weighted image through the region of the foramen of Monro. The lateral ventricles are dilated (curved white arrows). The third ventricle is inverted and filled by the suprasellar cyst. The walls of the cyst are faintly seen as a thin septum (long white arrows).
On MRI, the findings are similar to CT, although the bony changes may be more difficult to see. MRI offers two advantages over CT in this setting. First, the margins of the cyst may be seen as separate from the ventricles; second, the additional planes of imaging may also help to delineate the cyst from the dilated ventricles (see Fig. 20-6B and C). Also, MRI is more sensitive than CT in the detection of transependymal migration of CSF as an indication of obstructive hydrocephalus.
Septo-optic dysplasia is a congenital malformation of the midline structures with absence of the septum pellucidum and a hypoplasia of the optic nerves, optic chiasm, and pituitary gland (Fig. 20-7). Septo-optic dysplasia can be considered the mildest form of holoprosencephaly. The patients have a variable degree of endocrine dysfunction, often including diabetes insipidus. Either vision or endocrine symptoms may predominate. Usually plain radiographs are normal, but the sella may be small. CT demonstrates the absence of the septum pellucidum. The optic chiasm is usually small, and the pituitary gland may be normal in size or hypoplastic. The findings on MRI are similar to those on CT, demonstrating an absence of the septum pellucidum and a small optic chiasm and optic nerves.
FIGURE 20-7. Septo-optic dysplasia. This adult presented with polydipsia, diabetes insipidus, and optic atrophy. A, Coronal contrast-enhanced T1-weighted image through the suprasellar region. The frontal horns are somewhat deformed, and the septum pellucidum is not visible in the midline (open white arrow). The pituitary gland (black arrow) is small. The infundibulum is also small (solid white arrow). The optic chiasm is not well seen. B, Axial proton-density image through the lateral ventricle. Again, the columns of the fornix and the septum pellucidum (open white arrow) are absent.
Craniopharyngiomas (Fig. 20-8, Fig. 20-9, Fig. 20-10), which are formed from ectodermal elements of Rathke pouch, are composed of squamous epithelial structures. They can occur anywhere from the floor of the third ventricle (hypothalamus) to the pharyngeal tonsil, with the majority being found in the suprasellar region. These tumors have a bimodal incidence, with peaks in the first and fifth decades of life; they comprise 9% of pediatric brain tumors.19 Clinicopathologically, two distinct subtypes are recognized: the adamantinous, which tend to occur in children, and the squamous-papillary variants, which tend to occur in adults.20 Craniopharyngiomas may present because of a mass effect on the chiasm, headaches, hydrocephalus, or pituitary and hypothalamic dysfunction.
FIGURE 20-8. Cystic craniopharyngioma. A, Contrast-enhanced sagittal T1-weighted image through the midline. A 2.5-cm inverted, pear-shaped cystic mass (straight white arrows) fills the sella and extends into the suprasellar cistern. The regions of the optic chiasm and pituitary stalk are not well demonstrated. There is no hydrocephalus. B, Axial T2-weighted image through the suprasellar cistern. The cystic craniopharyngioma demonstrates high signal intensity (black straight arrows) similar to that of cerebrospinal fluid. The suprasellar carotid arteries (solid white arrow) are seen as low signal intensity flow voids. They are displaced laterally by the mass.
FIGURE 20-9. Mixed cystic and solid craniopharyngioma. This patient had a family history of multiple endocrine neoplasia syndrome type 1, with hypopituitarism. He did not have a primary pituitary tumor, but rather a craniopharyngioma. A, Axial contrast-enhanced CT scan through the suprasellar cistern. There is an irregular mixed-density mass filling most of the suprasellar cistern (curved white arrows). There are small calcifications (thick black arrow) within the central posterior portion of the mass. There is no hydrocephalus. B, Coronal CT scan through the region of the sella. The floor of the sella is completely destroyed (small black arrowheads), and the mass extends to fill much of the sphenoid sinus. The clinoids are not well defined, and there is a mixed-density, partially calcified mass in the suprasellar region (small black arrows). C, Coronal contrast-enhanced T1-weighted magnetic resonance image through the sella in a location similar to that of B. The mass demonstrates intense contrast enhancement. There is envelopment of the carotid artery on the left (straight black arrow). The lesion extends into the suprasellar cistern and obliterates the region of the optic chiasm and pituitary stalk (solid white arrow). The lesion also grows into the temporal and frontal lobes above the clinoids on the left (black arrowheads). The cystic spaces within the tumor are lower in signal intensity, similar to that of cerebrospinal fluid.
FIGURE 20-10. Solid sellar and suprasellar craniopharyngioma. A, Sagittal contrast-enhanced T1-weighted magnetic resonance imaging (MRI) scan through the midline demonstrates a large mushroom-shaped mass extending out of the deformed sella into the anterior third ventricle (black arrows). The mass obscures the optic chiasm and other anterior third ventricular structures. The mass is associated with hydrocephalus and expansion of the lateral ventricles and bowing of the corpus callosum. B, Anterior view reconstruction of a contrast-enhanced 3D gradient echo acquisition shows the large enhancing sellar and suprasellar mass (white arrows). The MR angiogram (MRA) demonstrates elevation of the anterior cerebral arteries bilaterally (black arrows).
If the lesion is large enough, plain radiographs of the skull demonstrate remodeling of the sella turcica and clinoid processes. The amorphous or curvilinear calcifications, which are present in most pediatric tumors and half of adult tumors, are more readily detected by CT than on plain radiographs.
On CT, craniopharyngiomas can be mixed cystic and solid and often exhibit enhancement of the more solid portions (see Fig. 20-9). Hemorrhage is not an uncommon finding, particularly within cystic portions of the tumors. Most commonly, these tumors are suprasellar in location. Craniopharyngiomas may grow to displace the optic chiasm superiorly, to displace the normal pituitary gland and stalk, to extend into the cavernous sinuses, and even to encase or occlude the carotid arteries.
The imaging characteristics of craniopharyngiomas on MRI are variable, reflecting the wide range of components histologically composing these tumors. The tumors may be cystic (see Fig. 20-8), mixed cystic and solid (see Fig. 20-9), or primarily solid (see Fig. 20-10). High signal intensity on T1- and T2-weighted images is seen in cysts with high cholesterol content or with subacute hemorrhage. Craniopharyngiomas can also be of low signal intensity on T1-weighted images if the cyst contains a large amount of keratin.21 Fluid levels can be seen in cystic regions. Adamantinous craniopharyngiomas tend to be primarily cystic or mixed cystic-solid lesions that occur in children and adults, whereas squamous-papillary subtypes tend to be predominantly solid or mixed solid-cystic and occur in adults. Distinguishing between the two has a prognostic significance, because adamantinous tumors tend to recur. MRI can be helpful in distinguishing between the two: Encasement of vessels, a lobulated shape, and the presence of hyperintense cysts is suggestive of adamantinous tumors; and a round shape, presence of hypointense cysts, and a predominantly solid appearance is seen with squamous-papillary tumors.20 The overall sensitivity for detecting tumor is higher with MRI, and the potential for displaying anatomy in multiple planes provides excellent data for surgical planning (see Fig. 20-10). Some lesions that can be confused with craniopharyngiomas include arachnoid cysts, dermoid tumors, meningiomas, and aneurysms (if calcified).
OPTIC CHIASM AND HYPOTHALAMIC GLIOMAS
Gliomas involving the optic chiasm and hypothalamus present an imaging problem. It is often difficult or impossible to separate the origin of these tumors because of their intimate association.22 If there is extension of tumor along the optic tracts or optic nerves, it is much easier to determine the site of origin, because there is a characteristic growth pattern for optic pathway gliomas but not for hypothalamic gliomas. Histologically, these gliomas, which are more common in children, are slow-growing pilocytic astrocytomas. Optic gliomas are more common in patients with neurofibromatosis type 1 (Fig. 20-11). In adults, optic gliomas tend to be more aggressive and usually represent glioblastomas. Usually, plain radiographs are not helpful, except when the tumors extend along the optic nerves and cause expansion of the optic canals. CT and MRI demonstrate enlargement of the optic chiasm or hypothalamus, which is particularly well seen on coronal images (see Fig. 20-11A). These lesions usually enhance homogeneously with both CT and MRI contrast-enhanced images, and, in the case of optic nerve tumors, there may be extension of abnormal signal and enhancement along the optic tracts and radiations. The differential diagnosis includes craniopharyngiomas, sarcoid, metastases, or lymphomas.
FIGURE 20-11. Hypothalamic and optic pathway glioma. This young man presented with vision problems. He had a history of neurofibromatosis, type 1. A, Coronal contrast-enhanced T1-weighted magnetic resonance image. The optic chiasm and hypothalamus (solid white arrows) are thickened and globular in configuration. The anterior third ventricular recess is not well seen. The pituitary stalk and pituitary gland (open white arrow) are normal in configuration. B, Sagittal non–contrast-enhanced T1-weighted magnetic resonance image. An irregular mass fills the anterior third ventricle, optic chiasm, and hypothalamic area (long thin white arrows). A segment of the lesion may be cystic and appears as low signal regions. The pituitary gland and infundibulum are normal (open white arrow).
Pituitary adenomas can be classified according to function and size. Lesions smaller than 1 cm are classified as microadenomas (Fig. 20-12), and those larger than 1 cm are classified as macroadenomas (Fig. 20-13, Fig. 20-14 and Fig. 20-15). The most common functioning adenomas are prolactinomas (see Chap. 13). Other functioning adenomas include adrenocorticotropic hormone-secreting tumors, thyroid-stimulating hormone-secreting tumors, and GH-secreting tumors (see Chap. 12, Chap. 14 and Chap. 15). Nonfunctioning adenomas account for ~40% of all pituitary adenomas. Adenocarcinomas of the pituitary gland are rare; in fact, metastasis to the gland is more common (see Chap. 11). Pituitary adenomas are usually seen in adults and are uncommon in children. When seen in childhood, they are usually seen in adolescent boys and are commonly macroadenomas, particularly prolactinomas that tend to be hemorrhagic.23
FIGURE 20-12. Pituitary microadenoma. This young woman presented with hyperprolactinemia. A, Sagittal T1-weighted non–contrast-enhanced magnetic resonance image. The anterior portion of the pituitary gland (solid white arrow) demonstrates slightly decreased signal. In general, the volume of the sella is not enlarged. The suprasellar structures are intact. B, Coronal contrast-enhanced T1-weighted image. The superior margin of the pituitary gland is slightly convex and asymmetrically enlarged on the right. The low signal microadenoma (measuring 8 5 mm) is seen on the right (small black arrows). The lesion crosses the midline. This section is anterior to the infundibulum and also shows the anterior cerebral arteries (small black arrowheads), the optic chiasm (straight white arrow), the supraclinoid carotid artery (curved white arrow), and the cavernous carotid arteries (large black arrowhead). A few of the cranial nerves in the cavernous sinus are also visible (small white arrows).
FIGURE 20-13. Acromegaly and macroadenoma of the pituitary. This is a sagittal non–contrast-enhanced T1-weighted image of the midline skull. The scalp is thickened (solid white arrow). The skull is also markedly thickened (straight black arrows). The frontal sinuses are expanded (open white arrow). The pituitary gland is enlarged (small black arrowheads) and fills much of the clivus and sphenoid sinus. It does not extend into the suprasellar cistern or involve the brainstem.
FIGURE 20-14. Pituitary macroadenoma. A, Coronal contrast-enhanced CT scan through the sella. The pituitary gland is slightly enlarged. The superior surface is bowed cephalad into the suprasellar cistern (straight white arrows). The optic chiasm and pituitary stalk are not significantly deformed. The floor of the sella may be partially eroded because there is no cortical margin (open white arrow). Involvement of the cavernous sinus and carotid arteries is not clearly demonstrated. B, Coronal magnetic resonance image at a level similar to that of Figure 20-14A. The soft-tissue contrast is much better. Again, the gland is slightly enlarged and measures >1 cm, with the superior margin (solid white arrow) protruding into the suprasellar cistern without coming in contact with the optic chiasm (open white arrow). The carotid arteries (solid black arrows) are displaced slightly laterally in the cavernous sinus regions. There does not appear to be clear-cut involvement of the cavernous sinus. C, Sagittal T1-weighted non–contrast-enhanced magnetic resonance image. Again, the small macroadenoma is seen filling the sella and remodeling the sella (solid white arrows). The clivus is slightly remodeled, and the posterior clinoids are not well defined. There is an incidental infarct in the pons (open white arrow).
FIGURE 20-15. Invasive pituitary macroadenoma. This coronal contrast-enhanced 3D gradient echo magnetic resonance image through the sella demonstrates a large irregular aggressive skull-base mass (white arrow) with the pituitary gland enhancing diffusely. The pituitary stalk is displaced to the right. The low-signal-intensity left carotid artery (black arrow) is enveloped by the mass and is displaced inferiorly. The mass protrudes into the left suprasellar cistern. It is in contact with the left medial temporal lobe after breaking through the left cavernous sinus. The mass is extending through the left foramen ovale into the masticator space.
The imaging appearance of pituitary adenomas is nonspecific, and no inference to histology can be made from the sellar patterns. However, additional clues may be present, related to other secondary endocrine changes. For instance, with GH-secreting tumors, acromegaly occurs, and one may visualize thickening of the scalp or enlargement of the mandible on radiograph or physical examination (see Fig. 20-13); these tumors tend to be larger than 5 mm. Cushing adenomas usually are microadenomas, but compression vertebral fractures and a “buffalo hump” deformity may be clues. Prolactinomas are more variable in size; they usually are microadenomas, but may be macroadenomas. Nonfunctioning tumors tend to be large.
Enlargement of the pituitary gland may result from many etiologies, not just neoplasia. End-organ failure is a cause of gland enlargement, such as is seen with primary hypothyroidism or surgical removal of the adrenals (Nelson syndrome; see later in this chapter and Chap. 75). If the functional status of a suspected adenoma or pituitary mass is in question, venous sampling of the petrosal sinuses can be performed by means of a catheter placed from the femoral vein into the internal jugular vein and then advanced into the greater petrosal veins.6 Analysis of blood samples can help determine the type of adenoma and the location of a lesion not detected by other imaging modalities. Sampling is also of value to demonstrate that the hormone originated from the gland rather than from an ectopic site. Although inferior petrosal sinus sampling is usually performed, it has been shown that bilateral, simultaneous cavernous sinus sampling, using corticotropin-releasing hormone, is as accurate as inferior petrosal sinus sampling in detecting Cushing disease and is perhaps more accurate in lateralizing the abnormality within the pituitary gland.24
The sella is usually normal in size with microadenomas and CT usually demonstrates no bony expansion, although there may be some asymmetry in the shape of the pituitary gland (see Fig. 20-12). CT, using thin-section coronal images and intravenous contrast, has been used successfully to detect microadenomas. The adenoma is identified as either a hypodense or hyperdense region in the gland after contrast enhancement. Cushing disease adenomas are more difficult to detect by CT, possibly because of their relative enhancement with respect to the normal gland.25
The recommended modality for examining a pituitary adenoma is MRI, with coronal and sagittal imaging. Detection is best with high-resolution techniques, such as three-dimensional imaging. The coronal plane is the most sensitive imaging plane, and T1-weighted spin-echo and three-dimensional imaging sequences are the best pulse sequences. The use of gadolinium enhancement is somewhat controversial,26,27 although the vast majority of radiologists believe that contrast is essential in the evaluation of the sella and parasellar regions. Usually, the tumors enhance less-than-normal tissue. Dynamic imaging can be of value in defining the abnormal segment of the gland.13
Of the pituitary macroadenomas, a higher percentage of these are nonfunctioning adenomas. Plain radiographs of the skull may demonstrate bony expansion or erosion of the sella; at times, the masses can be huge, with wide destruction of the skull base (to the extent that the site of origin is not clear). Calcifications are rare.
The sensitivity for detecting macroadenomas by CT is higher than for microadenomas; the CT examination should use thin-section coronal and axial imaging with intravenous contrast. Generally, the margins of the macroadenomas are more readily defined by MRI than by CT. Involvement of the optic chiasm, cavernous sinus, sphenoid sinus, orbit, temporal lobes, and carotid arteries can all be seen using MRI. In prolactinomas, MRI is used to evaluate the patient’s response to bromocriptine therapy. A decrease in tumor size can be seen as early as 1 week after the start of therapy. Additionally, MRI can detect posttherapy hemorrhage into macroadenomas and mass effect or inferior herniation of the chiasm as a result of a decrease in the tumor size.28 In macroadenomas, subacute hemorrhage is readily detected by MRI because the breakdown products of hemoglobin have paramagnetic or diamagnetic effects, depending on their chemical composition. Moreover, MRI is good for evaluating invasion into the adjacent cavernous sinus and for documenting the patency of the carotid arteries (see Fig. 20-15).
The thickness of the normal pituitary stalk averages 3.5 mm at the median eminence and 2.8 mm near its midpoint. The normal stalk enhances markedly on CT with contrast and on MRI with gadolinium. The most common clinical problem associated with disease of the pituitary stalk is diabetes insipidus. When this is present, there usually is absence of the normal hyperintensity of the posterior pituitary. On T1-weighted MRI, diabetes insipidus may be found to occur as a result of transection of the pituitary stalk.
The differential diagnosis of a thickened stalk includes sarcoidosis, tuberculosis, histiocytosis X, and ectopic posterior pituitary as well as germinoma. A thickened stalk can also be due to an extension of a glioma within the hypothalamus.
In patients with neurosarcoidosis and tuberculous infiltration of the stalk, the chest radiograph is generally abnormal and may be helpful in the differentiation from histiocytosis X. Clinically, patients with histiocytosis X may have skin lesions, otitis media, or bone lesions in addition to interstitial lung disease.12
A hamartoma of the tuber cinereum usually presents as precocious puberty in a young child.29 It is important to differentiate this lesion from a hypothalamic glioma because the prognosis for hamartoma is much more favorable. Imaging is best with MRI thin-section coronal and sagittal planes (Fig. 20-16). The findings are usually characteristic: The mass arises from the undersurface of the hypothalamus and is exophytic. The nodular mass (<1 cm) hangs into the suprasellar cistern adjacent to the mammillary bodies. On T1-weighted images, the signal is isointense with normal brain; on T2-weighted images, there is mild hyperintensity or isointensity. These lesions usually do not enhance with contrast administration.
FIGURE 20-16. Hypothalamic hamartoma. This young girl presented with precocious puberty. A, Non–contrast-enhanced sagittal T1-weighted image through the midline. A small nodule measuring ~5 mm in dimension (solid white arrow) is seen protruding from the under-surface of the hypothalamus into the suprasellar cistern just anterior to the mammillary bodies (small black arrowhead). The pituitary gland and infundibulum are normal (open white arrow). There does not appear to be any deformity of the anterior third ventricle or invasion of the brain. B, Axial proton-density magnetic resonance image. The small hamartoma (straight white arrow) is just anterior to the bifurcation of the basilar artery in the suprasellar cistern. The infundibulum is seen directly anterior to this (small black arrowhead). Other labeled structures include the supraclinoid carotid arteries (thin black arrows) and the posterior cerebral arteries (curved white arrows).
SELLAR AND PARASELLAR MENINGIOMA
Meningiomas usually occur in the parasellar region rather than within the true sella. They are derived from meningeal cells and are intimately associated with the dura. They can arise from the planum sphenoidale, the diaphragma sella, the optic nerve sheaths, the clinoids, or within the cavernous sinuses. Meningiomas may demonstrate calcification on plain radiographs. On CT, they are usually hyperdense and may be mistaken for hemorrhagic lesions or aneurysms. Hyperostosis of the adjacent bones, including the clinoids, is characteristic, and there may be expansion of the sphenoid sinus by air. On MRI, meningiomas tend to be isointense with gray matter and may be difficult to see on T1-weighted images without gadolinium. With both iodinated CT contrast agents and gadolinium MRI agents, meningiomas usually demonstrate marked, homogeneous enhancement.
SCHWANNOMAS AND NEUROFIBROMAS
Schwannomas, which are tumors derived from the myelin sheath of peripheral nerves, can be found involving the cranial nerves within the cavernous sinus and parasellar regions. In general, pituitary function is not affected; however, often the cranial nerves III, IV, V, and VI are affected within the cavernous sinuses or in the suprasellar and prepontine cisterns. Schwannomas may remodel the foramina of the skull where the individual nerves exit. When multiple lesions are seen, neurofibromatosis should be considered.
On CT, schwannomas usually are hyperdense lesions with homogeneous enhancement, and they may be hard to differentiate from meningiomas. On MRI, they may be isointense or hyperintense to gray matter on T1-weighted images, and they enhance homogeneously.
Metastasis to the sellar, suprasellar, or parasellar regions may arise in the sphenoid bone or sinus, cavernous sinus, pituitary gland, hypothalamus, or surrounding soft tissues (Fig. 20-17 and Fig. 20-18). Endocrine symptoms are uncommon with pituitary metastasis but are often seen when the hypothalamus is involved. It may be difficult to distinguish a metastasis from a primary pituitary abnormality on the basis of imaging alone; however, the presence of bony destruction or the history of a known primary tumor may be helpful.
FIGURE 20-17. Metastatic suprasellar and pituitary ependymoma. A, Coronal contrast-enhanced magnetic resonance imaging scan through the sella. The pituitary gland, stalk, and hypothalamus are all infiltrated by an aggressive irregular mass (white arrows). This is a secondary CSF seeding metastasis from a primary ependymoma of the lower thoracic cord. This type of pattern can be seen in sarcoid, histiocytosis X, eosinophilic granuloma, lymphoma, leukemia, and carcinoma. It is not uncommon that the sellar metastasis presents before the spinal or other primary tumor site. B, Sagittal T1-weighted midline thoracolumbar spin-echo image. The primary conus ependymoma (white arrows) is seen as an isointense expansile mass of the conus. Note that there is also thickening of some of the lower lumbar roots consistent with other drop metastases.
FIGURE 20-18. Hypothalamic and pituitary metastases. This patient presented with squamous cell carcinoma of the esophagus and diffuse metastatic bone disease. The patient became comatose. A, Sagittal non– contrast-enhanced T1-weighted magnetic resonance image. There is a 2-cm mass (solid white arrows) seen filling the anterior third ventricle and extending toward the pituitary. There is also deformity of the superior portion of the pituitary gland (curved white arrow). The low signal changes in the marrow of the clivus (black arrowhead) are secondary to metastatic disease in this area as well. B, T2-weighted axial image through the suprasellar region. There is an irregular mass (open curved white arrows) deforming the suprasellar cistern and displacing the adjacent vessels.
Suprasellar germ-cell tumors include seminomas (germinomas), teratomas, embryonal tumors, choriocarcinomas, and tumors of mixed histology. Some of these tumors are associated with simultaneous lesions in the pineal gland. These tumors are much more common in boys and tend to involve the pituitary stalk. When germ-cell tumors involve only the pituitary stalk, they can be difficult to differentiate from other primary processes involving the infundibulum (Fig. 20-19). If there is an associated pineal mass, it is virtually diagnostic of a germ-cell tumor.
FIGURE 20-19. Invasive pituitary germinoma. A, This coronal contrast-enhanced magnetic resonance imaging (MRI) spin-echo scan through the sella shows an expansile pituitary mass (white arrows) filling the sella. It protrudes into the suprasellar cistern (black arrow) and is displacing the adjacent brain structures cephalad. It does not appear to be invading the cavernous sinus. There is some odd contrast enhancement in the anterior third ventricle separate from the mass. B, Another coronal contrast-enhanced MRI spin-echo scan slightly farther anteriorly demonstrates that the germinoma is quite aggressive and is directly invading the left basal ganglion (black arrows).
Pituitary apoplexy is the result of necrosis of the anterior lobe of the pituitary. When seen in a postpartum woman, it is referred to as Sheehan syndrome. It is usually the result of hemorrhage into the gland, but may also be nonhemorrhagic in nature.30 Pituitary apoplexy is usually associated with hemorrhage into a preexisting adenoma, although it can occur in a normal gland (Fig. 20-20).30 Although CT in general is sensitive in making the diagnosis of acute hemorrhage, the changes in the pituitary gland may be difficult to appreciate. The imaging modality of choice for evaluation of hemorrhage in the pituitary is MRI. Also, this allows for evaluation of the optic chiasm, which may be compressed.
FIGURE 20-20. Hemorrhagic pituitary apoplexy. A, Sagittal T1-weighted spin-echo midline magnetic resonance imaging (MRI) demonstrates a high-signal-intensity abnormality of the sella (white arrow). It demonstrates bulging of the superior contour of the pituitary gland without major deformity of the optic chiasm. The high signal intensity without contrast suggests subacute hemorrhage. B, The pituitary apoplexy hemorrhage (white arrow) demonstrates low signal intensity on the T2-weighted axial image. This suggests that the hemorrhage is in the acute phase. Note the high-signal-intensity cerebro spinal fluid (CSF) spaces.
SPHENOID SINUS DISEASE
The sphenoid sinus can be involved with expansile (mucocele), inflammatory (Wegener granulomatosis), infectious (pyocele), or neoplastic (squamous cell carcinoma or lymphoma) processes. The inflammatory disease may cause irritation or may directly extend to involve the adjacent sella turcica. This is most severe with necrotizing infections (such as mucormycosis) in immunocompromised and diabetic patients. In this setting, it may be difficult to differentiate inflammatory from neoplastic disease, such as squamous cell or adenocarcinoma of the sphenoid sinus and chordoma of the clivus. Endocrine symptoms are rare.
Aneurysms may involve any of the intracranial vessels and are usually found at branch points. Aneurysms of the cavernous supraclinoid carotid and anterior cerebral arteries may be located in the sella or suprasellar region (Fig. 20-21). Compressive symptoms of aneurysms depend on their location. Aneurysms that extend into the suprasellar region may compress the optic chiasm; thus, patients may present with bitemporal hemi-anopia. Aneurysms may also compress the pituitary or infundibulum and present with diabetes insipidus or other endocrine abnormalities. If there has been a subarachnoid hemorrhage, the patient may present with severe headache or with a neurologic deficit related to vasospasm.
FIGURE 20-21. Supraclinoid internal carotid artery aneurysm. This patient presented with Cushing syndrome and no history of subarachnoid hemorrhage or headache. A, Sagittal non–contrast-enhanced T1-weighted image. There is a circular signal void measuring ~2 cm (short white arrows) in the suprasellar region. This is interposed between the optic chiasm (long white arrows) and the septal region of the frontal lobes. The pituitary gland (large black arrowheads) is essentially normal. B, Contrast-enhanced coronal T1-weighted magnetic resonance angiogram (MRA). The supraclinoid carotid aneurysm (solid black arrows) is seen to have a high signal rim at the periphery. This is related to the abnormal blood flow in aneurysms at the periphery rather than at the center of the lesion. The anterior cerebral arteries (small black arrowheads) and the pituitary stalk (open curved white arrow) are displaced to the left. The pituitary gland is normal.
On plain radiograph, curvilinear or ring-shaped calcifications may be seen in the wall of the aneurysm. Large aneurysms can remodel the skull base and erode the clinoids. On CT, these lesions tend to be of high density on unenhanced examinations, with marked enhancement after intravenous contrast. On spin-echo MRI images, aneurysms possess the characteristics of very low signal intensity or signal void and may demonstrate phase encoding or flow artifacts. MRA may be helpful in these cases, because it provides noninvasive screening for differentiating an aneurysm from some other causes of lesions of low signal intensity seen on the MRI (such as calcification). Arteriovenous malformations may also occur; they reveal characteristic large feeding arteries and several serpentine flow voids, representing the draining veins. Contrast angiography is still the gold standard for the evaluation of small aneurysms and arteriovenous malformations, but MRI can provide a good noninvasive screening examination in most cases. (See also ref. 30a and ref. 30b.)
Neurosarcoidosis has a propensity to involve the basilar cisterns and the suprasellar region, specifically the infundibulum. This is best evaluated with MRI, which can show thickening and enhancement of the meninges in the basal cisterns and surrounding the suprasellar cisterns as well as thickening of the normal pituitary stalk. In 3% to 16% of patients with sarcoidosis, the nervous system is involved, and sarcoidosis can mimic almost any other lesion.31,32
PRIMARY HYPOTHYROIDISM AND NELSON SYNDROME
Both primary hypothyroidism and Nelson syndrome33 represent hypertrophic changes to the pituitary gland caused by end-organ failure. In the case of primary hypothyroidism, thyrotropin-releasing hormone is hypersecreted because of the lack of feedback inhibition by thyroxine on the hypothalamus. The pituitary gland may be enlarged. In Nelson syndrome, adrenocorticotropic hormone is hypersecreted by a pituitary tumor, commonly after surgical removal of the adrenal glands for the treatment of Cushing syndrome. This causes hyperpigmentation of the skin and tumorous enlargement of the pituitary gland that can appear to behave aggressively and even metastasize outside of the cranial cavity (see Chap. 11, Chap. 14 and Chap. 75).
Many pituitary resections are performed by means of a trans-sphenoidal approach. In the postoperative patient, the floor of the sella is generally found to be distorted. The sphenoid sinus may be filled with implanted gelatin foam or biologic materials, such as muscle or fat. The gland itself may have an unusual shape (including club-shaped), or it may be in a lateral position, and the infundibulum may be deviated with respect to the center of the fossa (Fig. 20-22). If a frontal approach has been used, skull defects may be noted, and there often are focal areas of increased water content in the frontal lobes, suggesting local injury to the brain.
FIGURE 20-22. Postoperative changes. This patient had resection of a large pituitary adenoma. This coronal contrast-enhanced T1-weighted magnetic resonance image demonstrates displacement of the pituitary stalk to the left (curved solid white arrow). The floor of the sella is asymmetric and slopes inferiorly to the right. There is a cyst seen filling the residual sella (open white curved arrow). There is no mass displacing the stalk. This displacement is more likely related to postsurgical changes.
The pituitary gland may be found to have regenerated to a normal shape and size. Large suprasellar masses can deform the optic chiasm, but the chiasm may return to its normal size and location after the mass is gone. The chiasm may have herniated into the sella after being stretched (Fig. 20-23). There may be residual or recurrent tumor, particularly if the preoperative evaluation reveals extension into or invasion of the cavernous sinus. The sella may be partially empty in the postoperative patient. Because of these dynamic postoperative changes, the recommended time for follow-up examination is ~4 to 6 months after surgery to allow for resolution of hematomas, fluid collections, and resorption of implant packing materials.34,35
FIGURE 20-23. Postoperative sellar changes. A, Contrast-enhanced coronal T1-weighted magnetic resonance image. This patient had resection of a pituitary tumor. The anterior third ventricle and optic chiasm structures are herniated (long white arrows) into the region of the sellar surgical defect. The anterior cerebral arteries (solid black arrows) are displaced somewhat inferiorly as well. There is no residual mass. The floor of the sella is seen sloping far to the right. B, Sagittal non–contrast-enhanced T1-weighted magnetic resonance image. The hypothalamus and optic chiasm (long white arrows) are seen drooping in a J-like configuration into the surgical defect of the slightly expanded sella.
Imaging of the sella and pituitary fossa can be an important part of evaluating patients with endocrine or metabolic dysfunction. A review of the findings in both normal and diseased states has been presented. An emphasis has been placed on MRI, because in most cases, this has become the modality of choice for pituitary imaging.
Underwood LE, Radcliffe WB, Guinto FC Jr. New standards for the assessment of sella turcica volume in children. Radiology 1976; 126:651.
Reich E, Zelch JV, Alfidi RJ, et al. Computed tomography in the detection of juxtasellar lesions. Radiology 1976; 118:333.
Elster AD. Modern imaging of the pituitary. Radiology 1993; 187:3.
Kishore PRS, Kaufman AB, Melichar FA. Intrasellar carotid anastomosis simulating pituitary microadenoma. Radiology 1979; 132:381.
Raymond J, Hardy J, Czepko R, Roy D. Arterial injuries in transsphenoidal surgery for pituitary adenoma: the role of angiography and endovascular treatment. AJNR Am J Neuroradiol 1997; 18:655.
Miller DL, Doppman JL, Nieman LK, et al. Petrosal sinus sampling: discordant lateralization of ACTH-secreting pituitary microadenomas before and after stimulation with corticotropin-releasing hormone. Radiology 1990; 176:429.
Lusted LB, Keats TE. Atlas of roentgenographic measurement, 4th ed. Chicago: Year Book Medical Publishers, 1978:59.
Elster AD, Chen M, Williams DW III, Key LL. Pituitary gland: MR imaging of physiologic hypertrophy in adolescence. Radiology 1990; 174:682.
Dietrich RB, Lis LE, Greensite FS, Pitt D. Normal appearance of the pituitary gland in the first 2 years of life. AJNR Am J Neuroradiol 1995; 16:1413.
Doraiswamy PM, Potts JM, Axelson DA, et al. MR assessment of pituitary gland morphology in healthy volunteers: age- and gender-related differences. AJNR Am J Neuroradiol 1992; 13:1297.
Mark LP, Haughton VM. The posterior sella bright spot: a perspective.
AJNR Am J Neuroradiol 1990; 11:701.
Tien RD, Newton TH, McDermott MW, et al. Thickened pituitary stalk on MR images in patients with diabetes insipidus and Langerhans cell histiocytosis. AJNR Am J Neuroradiol 1990; 11:707.
Miki Y, Matsuo M, Nishizawa S, et al. Pituitary adenomas and normal pituitary tissue: enhancement patterns on Gadopentetate-enhanced MR imaging. Radiology 1990; 177:36.
Escott EJ, Rao VM, Ko WD, Guitierrez JE. Comparison of dynamic contrast-enhanced gradient-echo and spin-echo sequences in MR of head and neck neoplasms. AJNR Am J Neuroradiol 1997; 18:1411.
Chakeres DW, Curtin A, Ford G. Magnetic resonance imaging of pituitary and parasellar abnormalities. Radiol Clin North Am 1989; 27:267.
Kelly WM, Kucharczyk W, Kucharczyk J, et al. Posterior pituitary ectopia: an MR feature of pituitary dwarfism. AJNR Am J Neuroradiol 1988; 9:454.
Kurioiwa T, Okabe Y, Hasuo K, et al. MR imaging of pituitary dwarfism.
AJNR Am J Neuroradiol 1991; 12:161.
Benshoff ER, Katz BH. Ectopia of the posterior pituitary gland as a normal variant: assessment with MR imaging. AJNR Am J Neuroradiol 1990; 11:711.
Young SC, Zimmerman REA, Nowell MA, et al. Giant cystic craniopharyngiomas. Neuroradiology 1987; 29:468.
Sartoretti-Schefer S, Wichman W, Aguzzi A, Valavanis A. MR differentiation of adamantinous and squamous-papillary craniopharyngiomas. AJNR
Am J Neuroradiol 1997; 18:77.
Pusey E, Kortman KE, Flannigan BD, et al. MR of craniopharyngiomas: tumor delineation and characterization. AJNR Am J Neuroradiol 1987; 8:443.
Albert A, Lee BCP, Saint-Louis L, et al. Magnetic resonance imaging of optic chiasm and optic pathway. AJNR Am J Neuroradiol 1986; 7:255.
Poussaint TY, Barnes PD, Anthony DC, et al. Hemorrhagic pituitary adenomas in adolescence. AJNR Am J Neuroradiol 1996; 17:1907.
Oliverio PJ, Monsein LH, Wand GS, Debrun GM. Bilateral simultaneous cavernous sinus sampling using corticotropin-releasing hormone in the evaluation of Cushing disease. AJNR Am J Neuroradiol 1996; 17:1669.
Peck WW, Dillon WP, Norman D, et al. High-resolution MR imaging of pituitary microadenomas at 1.5 T: experience with Cushing disease. AJR
Am J Roentgenol 1989; 9:149.
Stadnik T, Stevenaert A, Beckers A, et al. Pituitary microadenomas: diagnosis with two- and three-dimensional MR imaging at 1.5 T before and after injection of gadolinium. Radiology 1990; 176:422.
Chong BW, Kucharczk W, Singer W, et al. Pituitary gland MRI: a comparative study of healthy volunteers and patients with microadenomas. AJNR
Am J Neuroradiol 1994; 15:675.
Lundin P, Bergstrom K, Nyman R, et al. Macroprolactinomas: serial MR imaging in long-term bromocriptine therapy. AJNR Am J Neuroradiol 1992; 13:1287.
Hahn FJ, Leinbrock LG, Huseman CA, Makos MM. The MR appearance of hypothalamic hamartoma. Neuroradiology 1988; 30:67.
Lavallee G, Marcos R, Palardy J. MR of nonhemorrhagic postpartum pituitary apoplexy. AJNR Am J Neuroradiol 1995; 16:1939.
Jager HR, Grieve JP. Advances in non-invasive imaging of intracranial vascular disease. Ann R Coll Surg Engl 2000; 82:1.
Wardlaw JM, White PM. The detection and management of unruptured intracranial aneurysms. Brain 2000; 123:265.
Hayes WS, Sherman JL, Stern BJ, et al. Magnetic resonance and CT evaluation of intracranial sarcoidosis. AJR Am J Roentgenol 1987; 8:1043.
Lexa FJ, Grossman RI. MR of sarcoidosis in the head and spine: spectrum of manifestations and radiographic response to steroid therapy. AJNR Am J
Neuroradiol 1994; 15:973.
Nagesser SK, van Seters AP, Kievit J, et al. Long-term results of total adrenalectomy for Cushing’s disease. World J Surg 2000; 24:108.
Steiner E, Knosp E, Herold CJ, et al. Pituitary adenomas: findings of postoperative MR imaging. Radiology 1992; 185:522.
Kaufman B, Tomsak RL, Kaufman BA, et al. Herniation of the suprasellar visual system and third ventricle into empty sellae: morphologic and clinical considerations. AJNR Am J Neuroradiol 1989; 10:65.