Spindle Cell Oncocytoma

**Semantic type:** Neoplastic Process

**Definition:** A very rare, WHO grade 1 neoplasm of the posterior pituitary. It is characterized by the presence of spindle cells with eosinophilic, granular cytoplasm forming fascicles. Electron microscopic studies demonstrate the accumulation of intracytoplasmic mitochondria and lack of secretory granules. Immunohistochemical studies are negative for pituitary hormones. Patients may present with pituitary hypofunction, visual disturbances, headache, nausea and vomiting. The clinical course is usually benign.

**Synonyms:** - Folliculo-Stellate Cell Tumor of the Pituitary - SCO - Spindle Cell Oncocytoma of the Adenohypophysis - Spindle Cell Oncocytoma of the Adenohypophysis (WHO Grade 1) - Spindle Cell Oncocytoma/Oncocytic Pituicytoma - Spindle cell oncocytoma