Spindle Cell Oncocytoma of the Adenohypophysis: A Case with Atypical Histomorphological Features and Early Recurrence

Spindle cell oncocytoma (SCO) of the adenohypophysis is an extremely rare sellar-region tumor that creates clinicopathologically relevant problems in the differential diagnosis and difficulties in patient management due to the limited data available regarding its biological behavior. A sellar/suprasellar mass was detected and surgery was performed in a 61-year-old male admitted for impaired vision. The patient was re-operated on twice due to persistence of symptoms and an increase in tumor size at the third and sixth postoperative month. The histopathological examination revealed tumor cells with oncocytic cytoplasm and spindle-epithelioid morphology fascicles/layers/pseudoacinar structures. Neoplastic cells showed a positive immunoreactivity with vimentin, epithelial membrane antigen, galectin 3, thyroid transcription factor-1, and anti-mitochondrial antibodies, and a negative immunoreactivity with epithelial markers, pituitary hormones, and neuroendocrine markers. Compared with the first biopsy sample, the material obtained from recurrent lesions was histologically characterized by increased pleomorphism, atypia, and mitotic activity. Although SCO is defined as Grade I according to the current World Health Organization classification, the considerable risk of early recurrence should be taken into account, especially in cases with atypia-pleomorphism and increased mytotic activity.