In common with other sellar region lesions generally and with Rathke's cleft cysts in particular, it seems likely that the origin of these lesions lies, at least in part, in disordered embryogenesis. In 1899, Mott and Barret [16] were the first to appreciate that these sellar and parasellar epithelial tumors might arise from the hypophy-seal duct or Rathke's pouch. Subsequently, craniopharyngiomas have been discovered along the path of development of Rathke's pouch from the pharynx to the sella. However, the pathology of RCCs and craniopharyngiomas differs and this might reflect the differing ability of squa-mous cell rests to undergo neoplastic change and form a craniopharyngioma or to persist as a simple cyst. The pathology is further complicated by the observation that certain cranio-pharyngiomas, particularly those presenting in childhood, resemble both adamantinomas or tooth bud tumors of the jaw and odontogenic cysts [17]. This raises the possibility of two separate tumor types, with the adult cranio-pharyngioma arising from squamous metaplasia of pituitary cells later in life. This would help to explain the differences seen in clinical presentation and response to treatment.

Most craniopharyngiomas appear near the infundibular stalk, distorting the surrounding anatomy and eventually obliterating the suprasellar cisterns.

Morphologically these lesions vary from predominantly solid to cystic. Mixed solid and cystic lesions are more common in pediatric series. Predominantly cystic tumors are more common across the age range, with predominantly solid lesions in only 10% of pediatric tumors. Cyst walls may be thin or thick structures impregnated with calcium deposits, and cyst fluid is dark green and laden with birefringent cholesterol crystals. Calcification is found in half of adult tumors and virtually all childhood tumors. Often there is a florid glial reaction around the craniopharyngioma, which is most marked around papillary-like tumor projections into the hypothalamus, making manipulation dangerous. Craniopharyngiomas are often adherent to major vessels, the chiasm and hypothalamus. This may preclude total removal.

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