Spindle cell oncocytoma of adenohypophysis: Cytogenetics and β-catenin findings with pathology differential diagnosis and review of the literature

Spindle cell oncocytoma (SCO) is an extremely rare neoplasm arising in the anterior pituitary. We report comprehensive pathological description of a case of SCO in a 60 year-old male who presented with nausea, vomiting and severe hyponatremia, and pan hypopituitarism. Magnetic resonance imaging (MRI) showed a 3.1 × 2.3 × 2.0 cm homogeneously enhancing bilobed mass within the sella turcica and suprasellar cistern. Intraoperative frozen section and touch imprint cytology showed cohesive spindle cells with abundant oncocytic cytoplasm. Histologic sections revealed the tumor was composed of interlacing fascicles of compact spindled cells with abundant dense oncocytic cytoplasm. There was no mitosis or necrosis present. Ki-67 index varied in areas, with an average of 3%. By immunohistochemistry (IHC), the tumor cells were negative for Cam5.2, AE1/3, neurofilament (NF), NeuN, glial fibrillary acidic protein (GFAP) and synaptophysin, and strongly positive for vimentin, TTF-1 and EMA. S-100 showed focal weakly positivity. By electron microscopy (EM), the cytoplasm of the spindle cells contained numerous abundant, back-to-back, uniform, round, normal-sized mitochondria with long and lamellar cristae. Beta-catenin showed diffuse membranous and partial cytoplasmic positivity. Cytogenetic analysis showed extra copies of chromosome 1 (74%, up to 8 copies), and loss of chromosome 2 (35%). The histogenesis, classification and differential diagnosis are discussed.