Chapter – Optic Chiasm, Parasellar Region, and Pituitary Fossa | Free Medical Textbook
The crossing over of optic nerve fibres at the optic chiasm allows the visual . to and between objects; and guiding body movements in relation to the objects seen. . Optic nerve glioma (or optic glioma), a form of glioma which affects the optic. Chiasmal syndrome is the set of signs and symptoms that are associated with lesions of the Gliomas of the optic chiasm are usually derived from astrocytes. The nasal fibers of each optic nerve decussate (cross) across the chiasm to the . Add links. This page was last edited on 12 December , at (UTC). were again consistent with low-grade astrocy- toma. Radiation hancing tumor is noted crossing . rectly from the chiasm-hypothalamus regions, thalamus.
Examination showed left optic neuropathy, temporal field loss of the right eye, and decreased corneal sensation. Estrogen and progesterone receptors may play a role in the growth of meningiomas. Also, cases of familial meningiomas have been reported. 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.
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. 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. In most Figure Glioma of the optic nerve, chiasm, and hypothalamus in a year-old girl. Invasion of the hypothalamus or third ventricle dramatically increases the mortality rate from this tumor.
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.
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.
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.
Optic chiasm | Revolvy
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. 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. 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. 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. 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 noted that the visual loss associated with sellar meningiomas Figure 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. 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. Regardless of the pattern, respect for the vertical midline is a feature that helps differentiate true chiasmal field patterns from other causes. 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. 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. 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 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. Compression of the posterior chiasm and its decussating nasal fibers may cause central bitemporal hemianopic scotomas e. 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.
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. 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. 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. Retinal conditions such as nasal sector retinitis pigmentosaoptic disc anomalies such as tilted optic discsand 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.
Also, lesions that block normal cerebrospinal fluid circulation may lead to headache, gait difficulties, somnolence and, eventually, urinary incontinence as a result of hydrocephalus. 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 prolactinomasgrowth hormone somatotropic adenomasadrenocorticotropin corticotropic adenomathyroid-stimulating hormone thyrotropic adenomaor 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. 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: 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.
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- Optic chiasm
- Optic Nerve Glioma
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. Bromocriptine usually is started at an initial dosage of 1. 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. 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 ?
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.
Low-grade oligodendroglial tumors include oligodendrogliomas and oligoastrocytomas WHO grade II tumors [ 1 ]. Low-grade glioneuronal tumors include the following WHO grade I tumors: In this review, we discuss the epidemiology, clinical, and diagnostic characteristics, histopathologic and molecular features, prognosis, and treatment of LGG.
For the purposes of this review, we will focus on supratentorial nonpilocytic astrocytomas, oligodendrogliomas, and oligoastrocytomas.
Selected other LGG subtypes, including subependymal giant cell astrocytoma SEGApleomorphic xanthoastrocytoma, brainstem glioma, and pilocytic astrocytoma, will be discussed briefly.
Available data do not separate high-grade versus low-grade tumors; thus, the annual incidence of LGG is difficult to determine. Incidence rates for oligodendrogliomas, anaplastic astrocytomas, glioblastomas, and mixed gliomas are more than two times higher in whites than in blacks [ 2 ]. The reason for this racial discrepancy is uncertain.
It may represent detection bias, a genetic difference, or another as yet unidentified explanation. Various environmental risk factors have been examined for evidence of a link between environmental exposures and an increased risk of brain tumor formation. The only factor definitively shown to be correlated with an increased risk of secondary brain tumors is CNS exposure to therapeutic or high-dose radiation [ 3 ].
Other environmental exposures have been investigated, without compelling evidence to support their role in brain tumor formation. However, these genetic conditions are found in only a very small percentage of patients diagnosed with LGG each year in the U.
Presentation LGGs present most commonly in the second through fourth decades of life, with peak incidence in the third and fourth decades of life. Clinical signs and symptoms vary and are largely attributed to mass effect from invasion into surrounding parenchyma or obstructive hydrocephalus [ 4 ].
Others may present with cognitive or behavioral changes, focal neurologic deficits, or clinical signs or symptoms of increased intracranial pressure, such as headache or papilledema.
Low-Grade Gliomas in Adults
However, patients may also be asymptomatic, without evident abnormalities on neurologic examination. Diagnosis Diagnosis of LGGs is made through a combination of imaging, histopathology, and molecular diagnostic methods. On computed tomography scan, low-grade gliomas appear as diffuse areas of low attenuation.