Answer: Craniopharyngioma

Histology: The lesion consists of a mixture of irregular nests of epithelial cells and abundant “wet” keratin. The epithelial nests display peripheral palisading of basaloid cells around “loosely” arranged central cells with pink to clear cytoplasm. The wet keratin has outlines of epithelial cells as well as calcification. There is adjacent and intermixed fibrovascular stroma. There is no overt squamous epithelium, cortical brain tissue, or necrosis.

Discussion: Craniopharyngiomas are low grade neoplasms that typically arise in the sellar region of the brain. There are two histologic subtypes, the adamantinomatous subtype and the papillary subtype. The adamantinomatous subtype typically occurs in children, but here it is seen in an adult; conversely, the papillary subtype is typically seen in adults. The papillary subtype is characterized by well differentiated squamous epithelium forming papillae and pseudopapillae, and it lacks the adamantinomatous epithelium and wet keratin.

The adamantinomatous subtype contains nests of epithelial cells that resemble the benign odontogenic tumor ameloblastoma (formerly called “adamantinoma” in the 1800s), which occurs in the mandible/maxilla. These nests of cells display peripheral palisading by columnar, basaloid cells that surround central loosely cohesive cells that resemble the central “stellate reticulum” area of a developing tooth. The adamantinomatous craniopharyngiomas also display abundant wet keratin.

Reference(s):
– Zada G, Lin N, Ojerholm E, Ramkissoon S, Laws ER. Craniopharyngioma and other cystic epithelial lesions of the sellar region: a review of clinical, imaging, and histopathological relationships. Neurosurg Focus. 2010 Apr;28(4):E4.