This benign tumor is derived from residual squamous epithelium found in the anterior lobe or infundibulum of the pituitary gland, and is virtually always located in the sellar and suprasellar area. This epithelial tissue is probably embryologically related to Rathke's cleft pouch, an outpouching of the primitive oropharynx that gives rise to the anterior pituitary gland. The tumor is often calcified and/or cystic with solid components. It can grow to enormous sizes and extend into the third ventricle and laterally into the temporal lobes. Since the epithelial elements are usually facing inwards, the products of this well-differentiated tissue produce keratin and cholesterol that accumulate within the tumor. Two histological types are described: (a) adamantinomatous, consisting of sheets of epithelial cells with a tendency to whorl, a palisade of columnar cells at the periphery, and containing 'wet' keratin; and, (b) papillary, consisting of epithelial tissue resting on a fibrous stroma, without wet keratin.
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