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Chapter 195 – Optic Chiasm, Parasellar Region, and Pituitary Fossa

Chapter 195 – Optic Chiasm, Parasellar Region, and Pituitary Fossa

 

RICHARD M. RUBIN

ALFREDO A. SADUN

ALFIO PAVA

 

 

 

 

 

DEFINITION

• Loss of vision and visual field related to involvement of the chiasm itself, its blood supply, or adjacent optic nerve or optic tract by tumor or other processes.

 

KEY FEATURE

• Binocular temporal field loss with respect to the vertical midline.

 

ASSOCIATED FEATURES

• Cavernous sinus symptoms such as ocular motor nerve palsies, Horner’s syndrome, trigeminal hypoesthesia, or pain.

• Endocrine dysfunction.

• Headache.

• Hydrocephalus.

• Endocrine dysfunction that arises from disruption of the hypothalamic–pituitary axis.

• Abnormalities of ocular motility, pupillary function, or facial sensation.

 

 

 

INTRODUCTION

The word chiasm derives from the Greek letter chi (?) and, in the visual system, refers to the appearance of the junction of the two optic nerves where they join to allow the hemidecussation of nasal fibers to the opposite optic tracts and the direct passage of temporal fibers to the ipsilateral optic tracts. Thus, all visual information supplied to both eyes from the right visual space is transmitted to the left cerebral cortex, and that supplied from the left visual space is transmitted to the right cerebral cortex.

The unique anatomy of the chiasm and its relationship to other major structures explains the characteristic patterns of visual loss, and cranial nerve, neurological, and endocrine dysfunction seen here ( Fig. 195-1 ).[1]

Anatomy

The optic chiasm, a flattened structure, is situated about 10?mm above the pituitary gland, which rests in the sella turcica of the sphenoid bone. [2] These structures are separated by a space called the suprasellar or inferior chiasmatic cistern. The chiasm also is contiguous with the anterior–inferior floor of the third ventricle at the base of the brain. The intracranial optic nerves and chiasm exit from the optic foramen and rise with a tilt of as much as 45°. Although the chiasm usually hangs directly over the pituitary fossa of the sella turcica, as a result of variations in the lengths of the optic nerves, the chiasm overlies the chiasmatic sulcus or the tuberculum sellae in 5% and 12% of cases, respectively (prefixed chiasm), and the dorsum sellae in about 4% of

 

 

Figure 195-1 Median sagittal section through the chiasm and relationship of chiasm to neighboring structures. The optic chiasm is suspended above the pituitary gland and rests in the sella turcica of the sphenoid bone. It is surrounded by cerebrospinal fluid, except posteriorly where it borders the anterior inferior wall of the third ventricle. (Adapted from Sadun AA, Rubin RM. Developments in sensory neuro-ophthalmology. In: Silverstone B, Lang MA, Rosenthal B, Faye EE, eds. The Lighthouse handbook on vision impairment and rehabilitation. New York: Oxford University Press; 2000.)

cases (postfixed chiasm) ( Fig. 195-2 ). [3] [4] The pituitary infundibulum, which arises from the hypothalamus (ventral diencephalon) behind the chiasm, extends downward to the posterior lobe of the pituitary (neurohypophysis). The anterior lobe of the pituitary (adenohypophysis) forms embryologically from Rathke’s pouch, an embryological structure connected to the pharynx. The chiasm is flanked laterally by the supraclinoid segments of the carotid arteries and inferolaterally by the cavernous sinuses ( Fig. 195-3 ). [5] The arterial supply of the chiasm is derived from the anterior cerebral and communicating arteries from above and the posterior communicating, posterior cerebral, and basilar arteries from below as the chiasm passes through the circle of Willis ( Fig. 195-4 ).[6] [7]

Although noted by Michel as early as 1887, Hermann Wilbrand described in several publications starting in 1904 a group of crossing, inferior nasal quadrant, extramacular ganglion cell axons that loop anteriorly into the posterior portion of the contralateral optic nerve before they turn posteriorly and laterally to head into the optic tract (Wilbrand’s knee).[8] In the early 1960s, Hoyt[9] [10] [11] and Luis[9] [10] confirmed, in the primate chiasm, the presence of Wilbrand’s knee and also demonstrated that the arrangement of axons within the optic chiasm is such that superior nasal quadrant retinal fibers remain superior and cross more posteriorly in the chiasm, that macular fibers cross through the chiasm in its central and posterior portions, and that arcuate fibers maintain their relative superior or inferior position while they pass through the chiasm ( Figs. 195-5 to 195-7 ).

 

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Figure 195-2 Variation in the length of the optic nerves alters the relative position of the chiasm to the sellar structures. Prefixed chiasm overlies the chiasmatic sulcus or the tuberculum sellae; normal chiasm overlies the diaphragma sellae; postfixed chiasm lies above the dorsum sellae. (Adapted from Rhoton AL, Harris FS, Renn WH. Microsurgical anatomy of the sellar region and cavernous sinus. In: Glaser JS, ed. Neuro-ophthalmology: symposium of the University of Miami and the Bascom Palmer Eye Institute, vol. IX. St Louis: CV Mosby; 1977:75–105.)

 

 

Figure 195-3 Coronal section through the optic chiasm and cavernous sinuses. The chiasm is flanked laterally by the supraclinoid segments of the carotid arteries and inferolaterally by the cavernous sinuses through which pass the oculomotor nerves and first two divisions of the trigeminal nerve. (Adapted from Warwick R. The orbital vessels. In: Warwick R, ed. Eugene Wolff’s anatomy of the eye and orbit, 7th ed. Philadelphia: WB Saunders; 1976:406–17.)

However, Horton[12] has suggested that Wilbrand’s knee is an artifact of the preparations studied.

EPIDEMIOLOGY AND PATHOGENESIS

Pituitary Adenomas

Chiasmal dysfunction most commonly occurs as a result of pituitary adenomas, which make up 12–15% of symptomatic intracranial neoplasms. Although uncommon before the age of 20 years, their incidence becomes increasingly greater after the fourth decade of life. Autopsy studies reveal that the prevalence of asymptomatic pituitary adenomas may be as high as 20–27% and that adenomatous hyperplasia may be found in almost every pituitary gland.[13]

The separation of the chiasm from the pituitary by the suprasellar or inferior chiasmatic cistern enables mild-to-moderate suprasellar extensions of pituitary tumors to occur without resultant

 

 

Figure 195-4 Relationship of the optic chiasm, optic nerves, and optic tracts to the arterial circle of Willis. The chiasm passes through the circle of Willis and receives its arterial supply from the anterior cerebral and communicating arteries from above and the posterior communicating, posterior cerebral, and basilar arteries from below. (Adapted from Reed H, Drance SM. The essentials of perimetry: static and kinetic, second ed. London: Oxford University Press; 1972.)

chiasmal visual field loss. When chiasmal visual loss is found in the presence of a pituitary tumor, advanced enlargement with expansion of the sella is expected ( Fig. 195-8 ). In contrast to endocrine-inactive pituitary tumors, which are detected when they reach a size that results in visual symptoms, endocrine-active tumors often cause systemic signs and symptoms before they affect the visual pathways.

Pituitary Apoplexy

Sudden enlargement of a pituitary adenoma may result from hemorrhage or infarction (pituitary apoplexy) and typically is associated with acute headache, visual loss, ophthalmoplegia, facial pain, or facial numbness ( Fig. 195-9 ). The normal pituitary gland also may undergo hemorrhagic or nonhemorrhagic infarction, but such episodes generally do not cause visual loss and may go unrecognized until hypopituitarism develops or

 

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Figure 195-5 Projections of the visual fibers from the upper and lower nasal quadrants in the primate. Upper nasal quadrant retinal fibers remain superior and cross more posteriorly in the chiasm. Lower nasal quadrant retinal fibers remain inferior, cross more anteriorly in the chiasm, loop anteriorly into the terminal portion of the contralateral optic nerve (Wilbrand’s knee), and head into the optic tract. (Adapted from Hoyt WF, Luis O. Visual fiber anatomy in the infrageniculate pathway of the primate: uncrossed and crossed retinal quadrant fiber projections studied with Nauta silver stain. Arch Ophthalmol. 1962;68:94–106.)

Figure 195-6 (Figure Not Available) Projections of the visual fibers from the lower and upper arcades in the primate. Arcuate fibers maintain their relative superior or inferior positions as they pass through the chiasm. Upper arcuate fibers enter the medial portion of each optic tract and lower arcuate fibers enter the lateral portion of each optic tract. A vertical line through the foveal center divides the nasal decussating from the temporal nondecussating fibers. (Adapted from Hoyt WF. Anatomic considerations of acute scotomata associated with lesions of the optic nerve and chiasm: a Nauta axon degeneration study in the monkey. Bull Johns Hopkins Hosp. 1962;111:57–71.)

autopsy is performed. Predisposing factors include pregnancy, estrogen therapy, obstetrical hemorrhage, diabetes mellitus, bleeding disorders, long-term anticoagulation, blood dyscrasias, radiation therapy, trauma, angiography, atheromatous emboli, cardiac surgery, coughing, positive pressure ventilation, and vasoactive agents.

 

 

Figure 195-7 Projections of the visual fibers from the papillomacular bundle in the primate. Macular fibers crossing through the chiasm do so in its central and posterior portions. (Adapted from Hoyt WF, Luis O. The primate chiasm: details of visual fiber organization studied by silver impregnation techniques. Arch Ophthalmol. 1963;70:69–85.)

 

 

Figure 195-8 Pituitary adenoma with chiasmal compression. Magnetic resonance scan from a 59-year-old woman who has a bitemporal hemianopia demonstrates a pituitary adenoma that bows the chiasm upward toward the third ventricle. The chiasm is thinned and draped over the mass.

Meningiomas

In 1929, Cushing and Eisenhardt[14] described the syndrome of bitemporal visual field defects and primary optic atrophy that occurred with a normal sella turcica as examined by radiography. This group of findings was associated most often with suprasellar meningiomas and aneurysms, or occasionally with craniopharyngiomas. Suprasellar meningiomas of the sphenoid planum or tuberculum sellae may compress the chiasm from below. Occasionally, the chiasm may be compressed posteriorly by meningiomas that arise from the diaphragma sellae, laterally by medial sphenoid ridge meningiomas, or above by olfactory groove subfrontal meningiomas.

Meningiomas represent 13–18% of all primary intracranial tumors. The incidence of these tumors increases with age. In one study of 464 patients who had meningiomas, 94% were over 30 years of age.[15] In other reports, less than 2% of meningiomas occur in patients under 20 years of age and, in this age group, only 2–4% of primary intracranial neoplasms are meningiomas.[16] Meningiomas that occur in adults are known to occur 2–3 times more frequently in women, but this predilection is not found

 

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Figure 195-9 Pituitary apoplexy (T1-weighted magnetic resonance image). Pituitary apoplexy in a 19-year-old man who gave a 1-year history of daily epistaxis and headache above the left eye, with more recent left-sided pain in the distribution of the ophthalmic division of the trigeminal nerve. Examination showed left optic neuropathy, temporal field loss of the right eye, and decreased corneal sensation.

with children. Estrogen and progesterone receptors may play a role in the growth of meningiomas.[17]

Von Recklinghausen’s neurofibromatosis (NF-1), an autosomal dominant inherited condition, is associated with meningiomas, often more than one in a single patient.[18] Multiple meningiomas have an incidence of 1–2% in most series. Also, cases of familial meningiomas have been reported. Both familial or multiple meningiomas may or may not be associated with von Recklinghausen’s syndrome.

Craniopharyngiomas

In children and young adults, embryonic vestigial epithelial remnants of Rathke’s pouch between the anterior and posterior lobes of the pituitary may develop into a benign, frequently cystic, tumor called craniopharyngioma. Such congenital tumors may occur at any age but have a bimodal incidence—the first peak occurs during the first two decades of life and the second between 50 and 70 years of age. They account for 2–4% of intracranial neoplasms, 8–13% of pediatric intracranial neoplasms, 20% of suprasellar masses in adults, and 54% of suprasellar masses in children.[19] Suprasellar, intrasellar, and (rarely) intrachiasmal involvement may be seen. Extension into the third ventricle is common and may lead to hydrocephalus. Rare posterior extension has been documented in association with ventral brainstem compression and with cerebellar compression.

Optic Gliomas

Gliomas, also called pilocytic astrocytomas, are not uncommon in the perichiasmal region and account for up to 10% of all intracranial neoplasms in adults and children ( Fig. 195-10 ). Although they may be diagnosed at any age, the majority are diagnosed during the first two decades of life. Women and girls are affected as often as men and boys. Many gliomas that infiltrate the chiasm also involve the hypothalamus. Although most are sporadic, up to one third may be associated with neurofibromatosis type 1.[20] [21] Gliomas in adults tend to be more malignant.[22]

Pregnancy

During pregnancy, pituitary adenomas (especially prolactinomas) and suprasellar meningiomas, which are sensitive to increased levels of estrogen and progesterone, may enlarge. In most

 

 

Figure 195-10 Glioma of the optic nerve, chiasm, and hypothalamus in a 13-year-old girl. Invasion of the hypothalamus or third ventricle dramatically increases the mortality rate from this tumor.

cases, visual symptoms abate after delivery or abortion. The normal pituitary gland also undergoes modest enlargement, but this enlargement is not enough to cause a chiasmal syndrome.

Lymphocytic adenohypophysitis, an immune-mediated diffuse lymphocytic infiltration of the pituitary gland, has been reported to cause chiasmal compression from suprasellar extension.[23] This uncommon condition has been reported in women only, and over one half of the cases have been found to occur during the perinatal period.

Other Causes of Chiasmal Syndrome

Less common neoplasms that affect the chiasm include chordoma (from the remnants of notochord that become sequestered during development), germinoma, endodermal sinus tumor, leukemia, Hodgkin’s and non-Hodgkin’s lymphoma, nasopharyngeal carcinoma, and metastatic carcinomas. Non-neoplastic mass lesions that may compress the chiasm include sphenoid sinus mucocele, arachnoid cyst, Rathke’s cleft cyst, epidermoid cyst, fibrous dysplasia, histiocytosis X, dolichoectasia of the internal carotid artery, and aneurysm of the large vessels of the circle of Willis or internal carotid artery. Cavernous hemangiomas, arteriovenous malformations, and venous angiomas may compress the chiasm; they frequently hemorrhage into the chiasm and cause chiasmal apoplexy. The chiasm also may be compressed from above when obstructive hydrocephalus leads to an enlarged third ventricle.[24] Extension of the normal subarachnoid space with prolapse and flattening of the chiasm into an enlargement of the sella turcica, known as the empty sella syndrome, may be associated with chiasmal dysfunction. As a result of the richly anastomotic blood supply of the chiasm, infarction requires multiple vessel involvement, such as with systemic vasculitis, radiation vasculopathy, or bilateral carotid occlusive disease.[25]

Inflammatory and infectious causes include sarcoidosis, syphilis, other granulomatous diseases, arachnoiditis, abscess, demyelination disease, and lymphoid hypophysitis. Head trauma also may result in a chiasmal syndrome. Postulated mechanisms include tears in the chiasm, contusion necrosis, compression from brain swelling, and delayed hemorrhage. Toxins have been implicated as causes of chiasmal injury, which include direct toxicity from chloramphenicol, isoniazid, ethambutol, hexachlorophene, vincristine, and ethchlorvynol, and hemorrhage associated with ethanol-induced coagulopathy. Congenital chiasmal dysplasia may be found in rare cases.

 

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OCULAR MANIFESTATIONS

Signs and Symptoms of Chiasmal Lesions

Chiasmal lesions cause signs and symptoms, such as loss of vision and visual field, related to involvement of the chiasm itself, its blood supply, the adjacent optic nerve, or the optic tract. Patients who have chiasmal involvement may be unaware of any deficit, may complain of difficulties related to unrecognized loss of their peripheral field, or may complain of unilateral or bilateral central or peripheral visual loss. If a complete bitemporal hemianopia is present, the affected person may experience loss of depth perception at near, the phenomenon of disappearance of an object as the point of fixation moves forward and leaves the object in an area of blindness behind ( Fig. 195-11 ), and “double vision” as a result of overlap or separation of the hemifields associated with a pre-existing phoria, a “hemifield slide” ( Fig. 195-12 ).

Generally, extrinsic mass lesions become apparent with gradually progressive depression of monocular or binocular vision. However, pituitary adenomas, craniopharyngiomas, or aneurysms may cause acute worsening or fluctuations of vision and can be mistaken for optic neuritis.[26] [27] [28] Fluctuation of vision over weeks and months also has been described in some cases of meningiomas, and optic disc pallor may be a late finding with these tumors. Response to treatment with systemic corticosteroids may further mimic the clinical picture of retrobulbar optic neuritis.

The pattern of field loss may suggest the presence of a lesion and further help to localize it ( Fig. 195-13 ). Compression of the anterior angle of the chiasm may cause a junctional scotoma, which is a central scotoma, or blindness in one eye plus a contralateral superotemporal defect. Hemianopic arcuate scotomas also may indicate early anterior chiasmal compression. Compression of the body of the chiasm from below, because of pituitary adenoma, for example, generally causes a bitemporal superior quadrantanopia or bitemporal hemianopia. Huber[29] noted that the visual loss associated with sellar meningiomas

 

 

Figure 195-11 Vision with a complete bitemporal hemianopia. Relative to the point of fixation is a triangular region of blindness behind, a triangular region of binocular vision in front, and regions of monocular vision to each side. As a result, an object may disappear as the point of fixation moves forward and leaves the object in an area of blindness behind. (Adapted from Kirkham TH. The ocular symptomatology of pituitary tumors. Proc R Soc Med. 1972;65:517–8.)

was more likely to be monocular or markedly asymmetrical if bilateral. Bitemporal inferior quadrantanopia or bitemporal hemianopia occurs with compression of the body of the chiasm from above, because of craniopharyngioma, for example. Compression of the posterior chiasm and its decussating nasal fibers may cause bitemporal hemianopic scotomas, but Traquair suggested that this pattern of field loss also may denote a rapidly growing tumor.[30] Less commonly, lateral compression of the margins of the chiasm (e.g., because of dolichoectasia of the carotid siphon or compression of the chiasm into lateral structures) may cause a nasal or binasal hemianopia. Regardless of the pattern, respect for the vertical midline is a feature that helps differentiate true chiasmal field patterns from other causes.

Because the chiasm is composed of the axons of retinal ganglion cells, chronic involvement (>6 weeks) of the chiasm often leads to nerve fiber layer defects or optic atrophy. When the body of the chiasm is involved, a temporal or “bow-tie” pattern, which corresponds to retinal fibers that originate nasal to the fovea, may occur ( Fig. 195-14 ). However, this appearance often is not apparent, because nondecussating fibers frequently are damaged, as well, particularly with compressive lesions. Optic atrophy also may be a late sign of chiasmal compression and is associated with a poorer postoperative visual acuity.

Signs and Symptoms of Parachiasmal Lesions

Parachiasmal involvement manifests with abnormalities of ocular motility, pupillary function, or facial sensation from injury to cranial nerves III, IV, V1, V2, or VI or the ocular sympathetic nerves in the parachiasmal region. Injury to these structures within the cavernous sinus may be associated with complaints of diplopia, ptosis, unequal pupil size, accommodative difficulty, facial pain or numbness, or eye pain. Signs include ocular motor nerve palsies, decreased sensation in the areas innervated by the first and second divisions of the trigeminal nerve, or Horner’s syndrome. Multiple cranial nerve involvement is more suggestive of invasive malignant tumors.

Lesions that block the normal cerebrospinal fluid circulation by obstruction of the foramen of Monro may result in hydrocephalus. Ocular examination may reveal vertical gaze abnormalities, convergence retraction nystagmus, pupillary light–near dissociation, and papilledema.

An unusual form of dissociated nystagmus called see-saw nystagmus occasionally accompanies mass lesions in the chiasmal region

 

 

Figure 195-12 Phenomenon of “hemifield slide.” In patients affected by a complete bitemporal hemianopia, preexisting phorias may result in separation of the hemifields vertically (hyperdeviation) or horizontally (esodeviation), or in double vision if the intact nasal hemifields overlap (exodeviation). (Adapted from Kirkham TH. The ocular symptomatology of pituitary tumors. Proc R Soc Med. 1972;65:517–8.)

 

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and diencephalon. Also, it may be seen transiently immediately after brainstem stroke, subsequent to severe head trauma after a delay of weeks to months, or as a variant of congenital nystagmus. See-saw nystagmus manifests as alternating intorsion and elevation of one eye with extortion and depression of the fellow eye and may result in complaints of oscillopsia. It ceases when the eyes are closed and does not occur in blind patients, which suggests a role for vision in its pathogenesis. A lesion that involves the interstitial nucleus of Cajal and its connections, or damage to the ocular counter-rolling mechanism mediated by the inferior olivary nucleus, has been postulated.

Chiasmal gliomas in young children have been reported to cause nystagmus, which may be the initial sign of chiasmal or parachiasmal involvement. The nystagmus, which is usually pendular and asymmetrical, may mimic spasmus nutans (even head nodding).

DIAGNOSIS

Visual Field Testing

The primary role of the clinician in the diagnosis of chiasmal disorders is to assess visual function accurately, interpret the results correctly and, thus, localize the region of anatomy affected. Visual field tests may provide a strong indication of direct chiasmal involvement, and failure to perform and properly interpret visual field tests is a common cause for delay in the diagnosis of chiasmal disorders. The technique is to establish that the vertical midline forms the border of the field depression and so rule out nonchiasmal temporal field loss that does not respect the vertical midline. Although a peripheral hemianopic step along the vertical midline is characteristic, early chiasmal compression often lacks a clear vertical step. Most often, temporal paracentral depression occurs

 

 

Figure 195-13 Localization and probable identification of masses by pattern of field loss. Junctional scotomas occur with compression of the anterior angle of the chiasm (sphenoid meningioma). Bitemporal hemianopia results from compression of the body of the chiasm from below (e.g., because of pituitary adenoma, sellar meningioma). Compression of the posterior chiasm and its decussating nasal fibers may cause central bitemporal hemianopic scotomas (e.g., because of hydrocephalus, pinealoma, craniopharyngioma).

because the chiasm has macular projections through most areas. A good strategy to establish a field defect attributable to chiasmal disease is to test either a single central isopter or static threshold sensitivity within the central 15–20° from fixation and to compare changes in color perception as colored objects pass across the vertical midline through central fixation.

Neuroimaging

Prompt magnetic resonance imaging (MRI) is indicated for the patient who has symptoms or signs referable to the chiasm or parachiasmal region (see Figs. 195-8 to 195-10 ) and is the study of choice for most sellar and parasellar lesions, but high-resolution computed tomography (CT) with fine cuts (1.5–3?mm) of axial and coronal views is an acceptable alternative. Both modalities provide about equivalent ability to detect lesions in the parachiasmal regions. The advantages of MRI are a better definition of the anatomical relationships to surrounding structures, the absence of artifacts from bone, and the ability to provide axial, coronal, and sagittal views without special image reconstruction. However, CT provides superior abilities in the detection of tumoral calcifications, of bony erosion and destruction by meningiomas and craniopharyngiomas, and of hyperostosis from meningiomas. Intravenous contrast and enhancement agents, such as paramagnetic gadolinium–pentetic acid for MRI and radiopaque iodine for CT, are used to demonstrate lesions that may not be visualized on noncontrast studies.

Other Diagnostic Testing

Complete endocrinological evaluation is obtained in the evaluation of lesions that involve the pituitary–hypothalamic axis. Lumbar puncture also may be required if an inflammatory or infectious cause is suspected. Magnetic resonance angiography or cerebral angiography may be indicated when vascular causes or cavernous sinus invasion are suspected, or to further characterize or delineate mass lesions and their blood supply. The current sensitivity of MRI or CT often obviates the need for angiography. Some clinicians still use arteriography to absolutely rule out a suprasellar aneurysm or to define the position of the carotid arteries prior to surgery. However, transsphenoidal resections of pituitary tumors usually are accomplished safely without prior angiography.

 

 

Figure 195-14 “Bow-tie” atrophy. Chronic compression of the decussating visual fibers of the chiasm leads to atrophy of the corresponding nasal retinal nerve fibers that enter the optic disc nasally and temporally. At the disc, this atrophy appears in a bow-tie pattern.

 

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DIFFERENTIAL DIAGNOSIS

Several conditions may mimic the visual field defects associated with chiasmal syndromes. Retinal conditions (such as nasal sector retinitis pigmentosa), optic disc anomalies (such as tilted optic discs), and papilledema with greatly enlarged blind spots may cause bilateral temporal field loss. Bilateral centrocecal scotomas caused by bilateral optic nerve disease may be difficult to differentiate from posterior chiasmal compression that affects the macular projections unless careful attention is paid to the vertical midline. Visual obstruction from overhanging redundant lid tissue, refractive scotomas, psychogenic visual loss, and test artifacts also may simulate chiasmal field patterns.

SYSTEMIC ASSOCIATIONS

Headache, usually frontal in location, frequently accompanies pituitary adenomas, pituitary apoplexy, and meningiomas and may be attributable to a stretched diaphragma sellae. Also, lesions that block normal cerebrospinal fluid circulation may lead to headache, gait difficulties, somnolence and, eventually, urinary incontinence (as a result of hydrocephalus). Abnormalities of pituitary endocrine dysfunction caused by disruption of the hypothalamic–pituitary axis or pituitary adenomas may lead to hypopituitarism, changes in hand or foot size because of acromegaly, amenorrhea–galactorrhea in women, impotence in men, or changes in body habitus that arise from Cushing’s syndrome. Hypothalamic dysfunction also may manifest as urinary frequency as a result of diabetes insipidus, heat or cold intolerance caused by a disturbance of temperature regulation, behavioral changes, lethargy, decreased libido, or disturbance of appetite. In children, delay or arrest in sexual development, precocious puberty, or infantile emaciation may occur.

PATHOLOGY

Pituitary Adenomas

Adenomas are by far the most common tumors of the pituitary gland, and usually arise as a discrete nodule from the anterior part of the gland, called adenohypophysis; they are soft and vary in color from gray–white to pink or red, depending on the degree of vascularity. Necrosis or spontaneous hemorrhage often leads to cystic areas.

For many years, pituitary adenomas were categorized as chromophobic, acidophil, or basophil adenomas with conventional staining methods. Currently, pituitary adenomas are categorized using combined immunohistochemical and light and electron microscopic techniques, serum concentrations of specific anterior pituitary hormones to define the nature of the hormones produced, and clinical picture. On the basis of these methods and the clinical picture, these tumors may be found to be monohormonal producers of prolactin (prolactinomas), growth hormone (somatotropic adenomas), adrenocorticotropin (corticotropic adenoma), thyroid-stimulating hormone (thyrotropic adenoma), or luteinizing with follicle-stimulating hormones (gonadotropic adenomas). Other tumors may be found to be producers of more than one hormone (plurihormonal adenomas) and up to one third may be composed of endocrinologically inactive cells (null cell adenomas). In a series of 1000 pituitary tumors surgically resected, Wilson[31] found that just over 77% were secretory (41% prolactin, 19% growth hormone, 17% adrenocorticotropin, and 0.2% thyrotropin). Gonadotropic adenomas are exceedingly rare. Occasionally, pituitary tumors are associated with other endocrine tumors in the pancreas and parathyroid gland (multiple endocrine neoplasia type 1).

Meningiomas

Meningiomas probably derive from cap cells that line the outer surface of the arachnoid (where they serve as the interface between the dura and arachnoid) and within the stroma of the choroid plexus. Histologically, meningiomas are categorized into:

• Syncytial tumors, in which the cell borders are indistinct because the cell membranes intertwine extensively

• Transitional tumors composed of plump polygonal cells and concentrically wrapped spindle cells that form whorls

• Fibroblastic meningiomas composed of interlacing bundles of elongated cells that simulate fibroblasts

• Angioblastic meningiomas in which prominent, thin-walled capillaries are found interspersed between the tumor cells

A characteristic feature of many meningiomas, especially those in which whorls are prominent, is the presence of psammoma bodies. These structures contain concentric layers of calcium salts, which appear to be deposited within degenerating whorl cells. Whorls and psammoma bodies, characteristic of transitional meningiomas, also may be found (but to a lesser degree) in fibroblastic meningiomas. Malignant meningiomas are rare and usually show cellular pleomorphism and mitoses. However, tumors that appear histologically benign and show rapid growth, local invasion, and metastasis may be determined malignant on the basis of biological behavior.

Craniopharyngiomas

Craniopharyngiomas may be solid or cystic; the cysts contain an oily fluid, with cholesterol clefts derived from degenerating epithelial cells and keratin. Histologically, the tumor’s solid portions may be composed of areas of trabeculae of stratified squamous epithelium supported by a vascularized connective tissue stroma, and of areas of peripheral, basal palisading cells that surround layers of stratified squamous epithelial cells, which may form “horny pearls” of keratinized cells. Calcification and deposition of lamellar bone are found frequently. The tumors are surrounded by a capsule of stratified squamous epithelium and, often, dense gliosis.

Optic Gliomas

In children, most gliomas are astrocytomas that consist of pilocytic cells (spindle-shaped cells with hair-like filaments) and stellate cells. Less often, the tumors may comprise evenly distributed oligodendrocytes with dark, round nuclei surrounded by clear haloes, which may stain with Alcian blue. These tumors have a benign appearance histologically. Eosinophilic hyalinization of apparently degenerated neuroglial cells may form elongated structures, called Rosenthal fibers. Formation of microcystic, acellular spaces that contain mucoid material is common. The benign tumors, which are more common in children, are distinct from the aggressive, malignant glioblastoma multiforme that predominates in adults.

TREATMENT, COURSE, AND OUTCOMES

Pituitary Adenomas

The medical treatment of pituitary tumors that are prolactin secreting consists of bromocriptine and other dopamine agonists that suppress further growth and reduce their size. Bromocriptine usually is started at an initial dosage of 1.25–2.5?mg daily and then increased by 2.5?mg every few days until a therapeutic response is obtained. A normal prolactin level may be achieved in up to 90% of microadenomas and in more than 70% of macroadenomas.[32] After the institution of bromocriptine therapy, shrinkage of tumor volume and reduction in serum prolactin may occur within days, and maximal shrinkage in tumor size appears to be obtained within 6 weeks. Improvements in visual acuity and field defects may be sustained using bromocriptine therapy in 80–90% of patients.[33] Unfortunately, about 15% of prolactinomas do not respond

 

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adequately to bromocriptine, and withdrawal of bromocriptine almost always results in tumor recurrence in those patients who did respond. Complications of bromocriptine therapy are uncommon but include cerebrospinal fluid rhinorrhea and chiasmal herniation.

Adenomas that secrete growth hormones also may respond to bromocriptine, but usually better results are obtained using octreotide, a somatostatin analog. Response rates of about 80% have been reported.[34] Tumors such as corticotropic adenomas and hormonally “inactive” pituitary tumors generally do not respond well to medical interventions.

Symptomatic pituitary tumors that are intolerant, unlikely to respond, or fail to respond to medical therapy usually are treated by surgical resection, most frequently by the transsphenoidal route. For prolactinomas, success rates depend on the initial tumor size and prolactin levels. Of patients with intrasellar microadenomas with prolactin levels under 155?ng/ml, 86% were found to have long-term remissions after transsphenoidal surgical removal.[32] Failure to obtain long-term remission after surgery correlates with higher initial prolactin levels, especially over 200?ng/ml.[35] Overall, recurrence of prolactinomas and pituitary adenomas that secrete growth hormone was 15% at 1 year after transsphenoidal surgery. Pretreatment with bromocriptine does not seem to improve surgical cure rates, although pretreatment to reduce tumor volume has been found to ease surgical removal. Improvement in vision after surgery may be delayed, and final visual outcome is not determined until 10 weeks postoperatively. Improvement does not usually extend beyond 3–4 months.

For patients who have prolactinomas and who become pregnant or intend to become pregnant, tumor growth must be anticipated. Options include early transsphenoidal resection if visual field loss is threatened or close observation of visual fields with resection of the tumor if visual field loss is found. Bromocriptine therapy is not recommended during pregnancy.

Incompletely resected tumors and those unresponsive to hormone therapy are considered for postoperative radiation therapy. Fractions must not exceed 200?cGy daily because of the increased incidence of radionecrosis. Extensive extrasellar extensions usually are treated with surgical decompression followed by irradiation of residual tumor, because a 40% incidence of microscopic dural invasion makes complete resections difficult or impossible to obtain with surgery alone.[36] Patients who have pituitary adenomas that do not immediately threaten vision may be considered candidates for stereotactic radiosurgery, such as with proton beam, cobalt-60 gamma knife, or linear accelerator therapy.[37] Although endocrine deficit commonly is associated with these modalities, other complications are infrequent and tumor recurrence is rare.

Pituitary Apoplexy

Pituitary apoplexy, which may be life-threatening, is treated with high-dose systemic corticosteroids (e.g., dexamethasone 6–12?mg every 6 hours) and hormone replacement, and may require medical management of either diabetes insipidus or inappropriate antidiuretic hormone secretion. If rapid visual loss occurs, decrease in level of consciousness, or no improvement within 24–48 hours, transsphenoidal decompression of the sella is indicated. Ischemic necrosis of the pituitary associated with apoplexy may lead to hypopituitarism. This scenario occurs commonly during the partum and postpartum periods (Sheehan’s syndrome). Most patients who have apoplexy require subsequent hormone replacement for pituitary insufficiency.

Meningiomas

The preferred management of meningiomas that involve the intracranial optic nerves and chiasm is surgical removal.[38] Surgical debulking alone, radiation therapy alone, or combination therapy may be performed if vital structures are surrounded densely by tumor. Postoperative radiation therapy of incompletely resected tumors appears to extend the period to tumor recurrence. However, because the tumors grow slowly and this treatment carries the risk of radiation vasculopathy, adjunctive radiation therapy is used only in cases in which progression follows incomplete resection. Another option in some patients includes hormone therapy using the progesterone antagonist mifepristone, which has resulted in reduced tumor size as shown by neuroimaging or improved visual fields in 5 of 14 patients.[39]

Location of the tumor and duration of visual symptoms are the most important predictors of visual recovery after surgical removal. Meningiomas of the tuberculum sellae generally are completely resectable and usually show visual recovery, whereas complete removal of sphenoid wing or diaphragma sellae tumors is most unlikely and visual improvement usually is not achieved. Complete gross excision alone does not rule out recurrence. One study showed a 19% 5-year probability of recurrence or progression of parasellar meningiomas despite “complete excision.” [40]

Craniopharyngiomas

The preferred treatment of craniopharyngiomas remains controversial. Although surgical resection of craniopharyngiomas usually is approached using craniotomy, subdiaphragmatic and cystic craniopharyngiomas may be approached transsphenoidally. Intracavitary placement of radioactive or chemotherapeutic agents, including phosphorus-32 colloid, yttrium-90 colloid, or bleomycin, within cystic tumors, has been attempted with some success.[41] Cystic tumors have a reputation of being particularly difficult to manage.

Recurrence is frequent with craniopharyngiomas and usually occurs during the first 2 years. Aggressive resections may delay recurrences but lead to greater mortality, as well as visual, endocrine, and neurological morbidity. A review of the ambitious attempts at complete surgical removal showed a 25% operative mortality, a 71% 11-year mortality, and residual tumor in over 75% of those autopsied.[42] Adjunctive radiation therapy improved median survival after extensive subtotal resection from about 3 years to more than 10 years and may achieve remission rates greater than 90%.[43] [44] However, adjunctive irradiation is reserved for patients over 5 years of age because of the complications of severe intellectual impairment and profound growth retardation that occur in children.

Visual recovery occurs in only 50% of patients after tumor resection, and the recovery seen within the first month is all that is expected. Lifelong endocrine replacement is expected in most patients after surgery or radiation therapy or both.[45]

Optic Gliomas

The treatment of optic chiasmatic–hypothalamic gliomas has been controversial.[46] [47] Patients with gliomas that involve the chiasm alone have a mortality of 28% because of the eventual involvement of the hypothalamus or third ventricle.[46] Invasion of the hypothalamus or third ventricle dramatically increases the mortality rate to more than 50% over 15 years (see Fig. 195-10 ).[46] Surgical intervention does not constitute a definitive treatment for these tumors once there is chiasmal or hypothalamic involvement and may be associated with significant visual morbidity and potential mortality. However, studies have shown benefit from tumor resection in those who have demonstrated rapid expansion of the suprasellar mass with visual deterioration or progressive neurological deficits.[47] [48] Shunting procedures are of clear benefit when hydrocephalus is present, and hormone replacement is indicated when endocrine dysfunction occurs. Chemotherapy for progressive chiasmal gliomas has shown promise and in children offers a safer alternative to radiotherapy.[49] Radiotherapy may be

 

1294

considered in children over the age of 5 years if progression occurs and chemotherapy has been ineffective.

 

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One comment on “Chapter 195 – Optic Chiasm, Parasellar Region, and Pituitary Fossa

  1. How can I find the figure?

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