Spindle cell oncocytoma (SCO)
General description
Spindle cell oncocytoma (SCO) is a rare, World Health Organization grade I nonfunctional neoplasm of the adenohypophysis first delineated in 2002. Although histologically benign, SCO often behaves aggressively owing to its hypervascularity, fibrous stroma, and adhesive growth.
SCO accounts for approximately 0.1–0.4% of all sellar tumors and has an estimated annual incidence of 0.01–0.03 per 100 000 population. It predominantly affects middle-aged to older adults, with a mean age at diagnosis of 56–62 years and the vast majority occurring between the fifth and eighth decades of life. There is no clear gender predilection.
Clinically, patients most often present with symptoms of mass effect, including visual field defects (up to 68%), headache, and varying degrees of hypopituitarism or panhypopituitarism in 37–73% of cases. Diabetes insipidus is not a recognized feature.
WHO Classification of Tumors the CNS 2021, 5th edition
According to the 2021 WHO Classification of Tumors of the Central Nervous System (WHO CNS5), pituicytoma, granular cell tumor of the sellar region, and spindle cell oncocytoma are classified together under the category "Tumors of the sellar region" as a single combined entity listed as "Pituicytoma, granular cell tumor of the sellar region, and spindle cell oncocytoma".
This represents a significant conceptual change from previous classifications. The 2021 WHO CNS5 recognizes these three entities as being grouped together in one section as a related group of tumor types, acknowledging that they most likely represent a spectrum of a single nosological entity unified by their common expression of thyroid transcription factor 1 (TTF-1). The decision to group these entities together is based on accumulating evidence from immunohistochemical, ultrastructural, and molecular analyses suggesting that pituicytoma, granular cell tumor, and spindle cell oncocytoma represent subtypes or morphological variations of a single entity with shared pituicyte lineage. Their common positivity for TTF-1, a marker of posterior pituitary cells, serves as the unifying diagnostic feature that supports this classification approach. Despite this conceptual unification, the classification maintains their separate designations because patient demographics and clinical outcomes vary among the three entities.
However, it is important to note that while the 2021 WHO CNS classification groups these tumors conceptually, the subsequent 2022 WHO Classification of Endocrine and Neuroendocrine Tumors has further refined this nomenclature, reclassifying spindle cell oncocytoma as "oncocytic pituicytoma" and granular cell tumor as "granular pituicytoma," emphasizing their relationship as subtypes within the broader pituicyte tumor family.
References
- Hasegawa, Hirotaka, et al. "A comprehensive study of spindle cell oncocytoma of the pituitary gland: series of 6 cases and meta-analysis of 85 cases." World neurosurgery 149 (2021): e197-e216.
- Louis, David N., et al. "The 2021 WHO classification of tumors of the central nervous system: a summary." Neuro-oncology 23.8 (2021): 1231-1251.
- Li, Jing, et al. "Oncocytic pituicytoma in a patient with Cushing’s disease: a case report and narrative literature review." Frontiers in Endocrinology 16 (2025): 1487120.
- Borges, Manuel Thomas, Kevin O. Lillehei, and B. K. Kleinschmidt-DeMasters. "Spindle cell oncocytoma with late recurrence and unique neuroimaging characteristics due to recurrent subclinical intratumoral bleeding." Journal of neuro-oncology 101.1 (2011): 145-154.
Pituitary mass
On MRI and CT, SCOs invariably arise from the anterior pituitary (adenohypophysis) and almost always present as combined intrasellar and suprasellar masses.
Margins are lobulated and infiltrative, without a true capsule. Cavernous sinus invasion occurs in a minority of cases, and sellar floor erosion is rare. The infiltrative border contributes to the difficulty of obtaining gross-total resection.
On noncontrast CT, the solid component of SCO is usually isodense to brain parenchyma. On T1-weighted imaging, the solid component is iso- to hypointense relative to cortex, while on T2-weighted imaging, most lesions are iso- to relatively hyperintense compared with gray matter.
Dynamic contrast-enhanced MRI shows an early, intense wash-in of gadolinium with a plateau phase, consistent with hypervascularity and punctate hypointense foci corresponding to hemosiderin deposits or flow voids. Enhancement is frequently heterogeneous, particularly in larger tumors, but homogeneous patterns are also observed.
SCO shows multifocal intratumoral microhemorrhages that may appear as blooming artifacts on susceptibility-sensitive sequences, but frank hemorrhage is uncommon. SCO rarely features true cystic degeneration, necrosis, or calcification.