Primary Tumors Of The Sellar Region Craniopharyngiomas

Representing only 3% of all intracranial tumors overall, the craniopharyn-gioma is nonetheless one of the more common destructive lesions of the sellar region. Virtually every aspect of craniopharyngioma biology is the subject of ongoing debate. Nagging uncertainties regarding its cellular origins, opposing surgical philosophies concerning the need for a radical approach to resection, and the relative controversy over its natural history all provide immediate stimulus for intellectual discussion.

Craniopharyngiomas are generally believed to be developmental lesions that arise from remnants of Rathke's pouch. Such embryonic remnants assume the form of epithelial "rests," deposited between the tuber cinereum and the pituitary gland, along the tract of an incompletely involuted hypophyseal-pharyngeal duct (1,2). Correspondingly, craniopharyngiomas can arise anywhere along this path. Craniopharyngiomas could also arise from the squamous metaplasia of normal cells situated on the pituitary stalk, as was once an alternative explanation of their origin. However, evidence in favor of such a view has been conflicting (1).

From the standpoints of size, location, contents, pathologic appearance, and overall clinical behavior, craniopharyngiomas encompass a broad biologic spectrum. At the one extreme are minute tumors of microscopic proportions situated wholly within a normal pituitary gland. At the other and more common extreme are larger tumors, whose progressive growth enables them to compress the pitu itary gland and stalk, optic apparatus, and hypothalamic structures. Frequently, these larger lesions also extend into the third ventricle causing hydrocephalus or permeate cerebrospinal fluid (CSF) spaces to gain access to the middle and posterior cranial fossae.

Craniopharyngiomas can be solid or cystic, and the overwhelming majority exhibit both features. The cyst contents, though classically described as "engine oil" in appearance and consistency, can range from a shimmering cholesterol-laden fluid to a brown-black purulent sludge mixed with desquamated debris. Calcification is a common feature of craniopharyngiomas, ranging from microscopic specks to palpable, even bone-like, concretions. Pathologically, the epithelial elements comprising these tumors can range from cuboidal to columnar, or squamous in appearance. There has been an increasing tendency to distinguish craniopharyngiomas as either classically adamantinomatous or papillary (1,3). Although the latter has been proposed as a distinct clinicopathologic entity featuring a predilection for adults, a less aggressive biology, and an overall favorable prognosis (4), so rigid a distinction may not be entirely justifiable, because papillary variants may simply reflect one component of the biologic heterogeneity so characteristic of craniopharyngiomas in general. More recent studies indicate no prognostic differences between these two variants (5,6)

Topologically, approx 80% of craniopharyngiomas arise in and maintain a suprasellar location (Fig. 1).

These lesions are often tenaciously adherent to, and occasionally invasive of, the optic apparatus, hypothalamus, pituitary stalk, cranial nerves, vascular structures, and surrounding brain parenchyma. Emphasis has also been placed on the exuberant gliotic nature of the brain parenchyma at the tumor-brain interface and its suitability as a safe surgical plane facilitating tumor removal. Approx 20% to 30% of craniopharyngiomas originate within the sella, resulting in its enlargement in a fashion similar to that seen with pituitary adenomas. Rare examples of craniopharyngiomas wholly situated within the third ventricle, optic chiasm, or sphenoid bone have been reported (1,3).

The clinical presentation of craniopharyngiomas is determined by the age of the patient and the size and location of the tumor (2,7). In general, symptoms can be categorized as endocrine, visual, cognitive, and those deriving from increased intracerebral pressure (ICP).

Endocrine dysfunction is more obvious in the pediatric population, primarily as retardation of growth and sexual development (8). In adults, endocrine symptoms are often subtle, particularly those related to partial hypopituitarism. The effects of combined hypogonadotrophinemia, together with moderate hyperprolactinemia from stalk or hypothalamic compression, are generally more obvious, presenting in young women especially as amenorrhea and occasionally galactorrhea. DI may coexist in all age groups.

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