Pituitary Gland, Spindle cell oncocytoma

Spindle cell oncocytoma is a rare, benign tumour of the pituitary gland classified as WHO grade I. Along with granular cell tumour (of the infundibulum/neurohypophysis), it is considered a variant of pituicytoma due to shared TTF-1 immunoreactivity. Clinically, it is usually indistinguishable from non-functioning pituitary adenomas. Microscopically, the tumour is composed of fascicles of eosinophilic (oncocytic) spindle cells admixed with epithelioid cells. The oncocytic cytoplasm correlates with abundant mitochondria seen on electron microscopy.