This is a histologically benign epithelioid tumor, generally assumed to originate from cell rests (remnants of the Rathke pouch [or adenohypophyseal diverticulum]) at the junction of the infundibular stem and pituitary gland. By the time the tumor has attained a diameter of 3 to 4 cm, it is almost always cystic and partly calcified. Usually it lies above the sella turcica, compressing and elevating the optic chiasm and extending up into the third ventricle. Less often it is subdiaphragmatic, that is, within the sella, where it compresses the pituitary body and erodes one part of the wall of the sella or a clinoid process; seldom it balloons the sella like a pituitary adenoma. Large tumors may obstruct the flow of CSF.
The tumor is oval, round, or lobulated and has a smooth surface. The wall of the cyst and the solid parts of the tumor consist of cords and whorls of epithelial cells (often with intercellular bridges and keratohyalin) separated by a loose network of stellate cells. If there are bridges between tumor cells, which have an epithelial origin, the tumor had in the past been classed as an adamantinoma, a term not used in recent classifications. The cyst contains dark albuminous fluid, cholesterol crystals, and calcium deposits; the calcium can be seen in plain films or CT of the suprasellar region in 70 to 80 percent of cases. The sella beneath the tumor tends to be flattened and enlarged. The majority of the patients are children, but the tumor is not infrequent in adults, and we have encountered patients up to 60 years of age.
The presenting syndrome may be one of increased intracranial pressure, but more often it takes the form of a combined pituitary-hypothalamic-chiasmal derangement. The symptoms are often subtle and long standing. In children, visual loss and diabetes insipidus are the most frequent findings, followed in a few cases by adiposity, delayed physical and mental development, headaches, and vomiting. The visual disorder takes the form of dim vision, chiasmal field defects, optic atrophy, or papilledema, as emphasized long ago by Kennedy and Smith. In adults, waning libido, amenorrhea, slight spastic weakness of one or both legs, headache without papilledema, failing vision, and mental dullness and confusion are the usual manifestations. One of the most remarkable cases in our experience was a middle-aged nurse who became distractible and ineffective at work and was thought for many months to be simply depressed. Often it is observed that drowsiness, ocular palsies, diabetes insipidus, and disturbance of temperature regulation (indicating hypothalamic involvement) occur later. Spontaneous rupture of the cystic lesion can incite severe aseptic meningitis, at times with depressed glucose in the CSF, a syndrome similar to that caused by rupture of the earlier described cholesteatoma.
In the differential diagnosis of the several craniopharyngioma syndromes, a careful clinical analysis is often more informative than laboratory procedures. Among the latter, MRI is likely to give the most useful information. Often, because of the cholesterol content, the tumor gives an increased signal on T1-weighted images. Usually, the cyst itself is isointense, like CSF, but occasionally it may give a decreased T2 signal.