A 61-year-old man with hyponatremia.

The case of a 61-year-old man presenting with dizziness, nausea, vomiting, reduced serum osmolality, and hyponatremia is reported. Endocrinologically, low levels for ADH, cortisol and testosterone as well as low-normal values for ACTH, LH and FSH were detected. Cranial computed tomography and MRI scans revealed an intra- and suprasellar tumor of adenoma-like appearance with elevation of the optic chiasm. No infiltration of the cavernous sinus was seen. After transsphenoidal resection of the tumor, no additional anterior lobe insufficiencies or diabetes insipidus occurred. Histological examination revealed a tumor consisting of spindle-shaped cells of uniformly high cellularity with no evidence of hypocellular areas. A cellular schwannoma was diagnosed. An intrasellar cellular schwannoma clinically and radiologically mimicking a non-secreting pituitary adenoma is uncommon. However, rare entities like schwannomas, melanocytomas or pituicytomas have to be considered in addition to the more common tumors like pituitary adenomas and meningiomas.