Endocrine Abstracts

Spindle Cell Oncocytoma (SCO) is a neoplasm of the adenohypophysis, often pre-operatively misdiagnosed as pituitary macroadenoma due to its rarity. First described in 2002, 28 cases have been described. It is a benign tumour manifesting in adults with no sex predilection, classified as WHO Grade I. A 71-year-old woman presented with bitemporal hemianopia, secondary hypoadrenalism, hypothyroidism and hypogonadotrophic hypogonadism. Imaging in October 2017 confirmed a 18.0×27.0×21.0 mm supra-sellar mass with optic chiasm displacement, suggestive of a pituitary macroadenoma. Appropriate hormone replacement was commenced and the same month, tumour resection by an endoscopic endonasal transsphenoidal approach was achieved. The tumour appeared firm and hypervascularised and debulking was associated with unexpected haemorrhage. Post-operative bitemporal hemianopia and visual acuity improved and imaging showed good decompression of the optic chiasm with some persistent suprasellar tumour and no signs of cavernous sinus invasion. She was discharged with no neurological sequalae on appropriate hormone replacements. Rather than the expect results, however, pathology revelated a Spindle Cell Oncocytoma (SCO), showing a proliferation of spindle cells arranged in short fascicles with eosinophilic cytoplasm and eccentric nuclei containing fine granular chromatin. Immunohistochemistry showed the tumour was positive for S-100 protein, epithelial membrane antigen(EMA), thyroid transcription factor-1 (TTF-1) and vimentin, typical of SCO. Ki67 was expressed in 10% of the neoplastic cells and p53 in 4%. Considering the low-grade and long natural history of SCO, pituitary radiotherapy may be required pending imaging and neuro-ophthalmology assessment. Our case was pre-operatively misdiagnosed as a pituitary macroadenoma and highlights that although rare, SCO masquerading as a macroadenoma remains an important differential diagnosis.