Chapter – Optic Chiasm, Parasellar Region, and Pituitary Fossa | Free Medical Textbook
The unique anatomy of the chiasm and its relationship to other major The optic chiasm is suspended above the pituitary gland and rests in. The most common disorder affecting the optic chiasm is a pituitary adenoma. and regulates many different glands, organs, and hormones. The pituitary gland is a pea-sized oval structure, of dura mater that covers the pituitary gland), optic chiasm.
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 Pituitary Gland - Structure - Vasculature - TeachMeAnatomy
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. 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. 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 ? Pituitary Apoplexy Pituitary apoplexy, which may be life-threatening, is treated with high-dose systemic corticosteroids e.
The visual impact of pituitary tumours
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. 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.
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. 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. 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 colloid, yttrium colloid, or bleomycin, within cystic tumors, has been attempted with some success. 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. Lifelong endocrine replacement is expected in most patients after surgery or radiation therapy or both.
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. Chemotherapy for progressive chiasmal gliomas has shown promise and in children offers a safer alternative to radiotherapy.
Correlative functional anatomy of the optic chiasm— Anatomical variations in the pituitary gland and adjacent structures in autopsy cases. Reed H, Drance SM. Arterial blood supply of the human optic chiasm and surrounding structures.
Schema des verlaufs der sehnervenfasern durch das chiasma. Hoyt WF, Luis O. Paper presented at Update in Neuro-ophthalmology meeting; ; San Francisco. These tumors behave according to their cell of origin and are named for the specific hormone they produce. For example, a prolactinoma grows from prolactin-producing cells. Nonfunctioning pituitary tumors do not secrete hormones. Instead, they grow until their size and mass effect cause headache, vision loss, nausea, vomiting, or fatigue.
These tumors may compress the normal pituitary gland decrease hormone production hypopituitarism. Based on size, pituitary tumors may be classified as microadenomas less than 10mm or macroadenomas larger than 10mm.
Large tumors can press on the optic nerves and invade the cavernous sinuses, which house the carotid arteries and the nerves involved in eye movement. These grow from embryonic remnant cells in the pituitary gland. Craniopharyngiomas typically grow from the pituitary stalk upward into the third ventricle and cause symptoms similar to pituitary adenomas. What are the symptoms? Symptoms of a pituitary tumor vary depending on its size and hormone secretion; many are asymptomatic.
The most common pituitary tumor, a prolactinoma, causes an overproduction of the hormone that helps control sexual function. In women, the tumor can cause menstruation to stop amenorrhea or inappropriate production of breast milk galactorrhea. In men, prolactinomas may cause enlarged breasts gynecomastiaerectile dysfunction or impotence, infertility, decrease in body hair, and low sex drive.
More common in men, these pituitary tumors may cause gigantism in children or acromegaly in adults. Symptoms include enlargement of the bones in the hands, feet, or face. Other symptoms include excess sweating, high blood pressure, heart disease, diabetes, and arthritis. Adrenocorticotropic hormone ACTH -producing tumors.
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More common in women, these tumors stimulate the adrenal gland to secrete cortisol. Excess cortisol causes Cushing's disease, a fatty hump between the shoulders; weight gain in the face, neck, and trunk of the body; and pink or purple stretch marks on the skin.
TSH-secreting tumors can cause hyperthyroidism. Hyperthyroidism can accelerate the body's metabolism, causing sudden weight loss, irregular heartbeat, and nervousness or irritability. Non-secreting tumors have few symptoms and are difficult to recognize until they grow quite large. These tumors can press against nearby optic nerves, causing headaches or vision loss. They can also impair hormone secretion from the pituitary gland, which can cause fatigue, weakness, loss of body hair, and pale skin.
In rare instances, a pituitary tumor can suddenly bleed hemorrhage. Symptoms include sudden onset of a severe headache and vision changes, including vision loss, double vision, or drooping of an eyelid. Pituitary apoplexy requires emergency treatment, usually with corticosteroids and often surgery.
What are the causes? The cause of pituitary tumors is unknown. Some researchers believe they occur when a cell in the pituitary gland becomes abnormal or mutates. Multiple endocrine neoplasia type 1 MEN 1 is a rare condition with simultaneous tumors of the pituitary, pancreas and parathyroid glands. They can occur at any age, but are more common after puberty. How is a diagnosis made? If you have symptoms that suggest a pituitary tumor, your physician will work with a team of specialists to confirm the diagnosis.
This team may include a neurosurgeon, otolaryngologist ear, nose, and throat surgeonendocrinologist, ophthalmologist, radiologist, and pathologist.
First, the doctor will obtain your personal and family medical history and perform a physical examination. In addition to checking your general health, the doctor performs a neurological exam to check mental status and memory, cranial nerve function, muscle strength, coordination, reflexes, and response to pain. Other tests may include: Magnetic Resonance Imaging MRI scan uses a magnetic field and radiofrequency waves to give a detailed view of the soft tissues of the brain.
A dye contrast agent may be injected into your bloodstream Fig. An MRI scan of a pituitary macroadenoma orange line that has expanded upward to compress the optic chiasm. Endocrine evaluation measures hormone levels in the blood or urine to detect abnormal levels caused by pituitary tumors. A visual field acuity test detects vision loss and missing areas in the field of view. This test measures both central and peripheral vision.
Petrosal sinus sampling is a procedure to draw blood from the veins that drain the pituitary gland. Similar to an angiogram, flexible catheters are inserted into the femoral veins in the groin.
The catheters are advanced to the petrosal veins near the pituitary. What treatments are available? Treatment options vary, depending on the type, grade, size, and location of the tumor, and your age and general health. Medication, surgery, and radiation either alone or in combination, are used to treat pituitary tumors and return hormone levels to normal. Specifically, in this patient the left optic nerve and the optic chiasm were most affected, as evidenced by the visual acuity loss OS and the temporal visual field loss OD with preservation of visual acuity.
Thus, our chief concern was for a sellar mass. It is important to note that while a sellar mass may present with bitemporal hemianopia, the combination of findings described above describing a junctional scotoma also localizes to the sellar area, and additional workup is indicated.
It is also useful to note that while the classic presentation of junctional scotoma includes central visual field loss in one eye and superotemporal field loss in the contralateral eye, the vision loss in the contralateral eye need not be supertemporal, and was not in this case.
A few radiologic clues can help differentiate between the various types of sellar masses. Craniopharyngioma is notable for its heterogenous radiographic appearance, often containing cysts and calcifications, which are best viewed on computed tomography CT. The pituitary adenoma typically lacks these features, though heterogeneity may be present if hemorrhage has occurred.
Pituitary adenoma is the most common cause of the chiasmal syndrome , and may present at any age. The pituitary gland produces a variety of hormones, and as such a pituitary tumor may be secretory or nonsecretory. Classically, the nonsecretory tumor presents with vision loss, whereas patients with secretory tumors are usually referred to ophthalmologists for evaluation after having already been diagnosed because of endocrine derangements.
Pituitary Apoplexy The dreaded complication of pituitary adenoma, and one with which the ophthalmologist must be familiar, is pituitary apoplexy. This life-threatening complication results from acute hemorrhage or infarction of the tumor.
Reported incidence varies between 0.