Xanthomatous hypophysitis with optic chiasm edema: First documented clinical case.

Xanthomatous hypophysitis is an exceedingly rare subtype of hypophysitis that can closely mimic a cystic pituitary adenoma. We report the case of a 54-year-old woman who presented with persistent headaches, intermittent ocular pain and signs of central diabetes insipidus. MRI revealed a cystic sellar mass with suprasellar extension demonstrating an atypically hyperenhancing capsule on early dynamic postcontrast imaging, and anterior rightward deviation of the infundibulum, initially interpreted as a cystic pituitary macroadenoma. Notably, there was an unusual nonenhancing T2-hyperintense signal in the adjacent optic chiasm, suggestive of edema despite the absence of direct chiasm compression and absence of the posterior pituitary bright spot. Endoscopic endonasal resection demonstrated firm yellow tissue, and histopathology confirmed xanthomatous hypophysitis characterized by aggregates of foamy macrophages. This case underscores the diagnostic challenges posed by xanthomatous hypophysitis, given its radiologic similarity to cystic pituitary adenoma. We highlight distinctive imaging findings, including capsular hyperenhancement with respect to the pituitary on dynamic post contrast imaging, lesion's origin in the posterior aspect of the pituitary, absence of the posterior pituitary bright spot and optic chiasm edema without compression. Based on the available literature, this represents the first reported case of optic chiasm edema associated with noncompressive xanthomatous hypophysitis.