Spindle cell oncocytomas of the pituitary gland

Last revised by Frank Gaillard on 21 Feb 2022

Spindle cell oncocytomas of the pituitary gland, also referred to as adenohypophysis spindle cell oncocytomas, are rare, low-grade nonfunctional tumors commonly showing clinical and radiologic presentations mostly indistinguishable from the much more common non-secretory pituitary macroadenomas

These tumors were only listed in the 4th edition (2007) of the WHO classification of the central nervous system tumors. 

In the 5th edition (2021) of the WHO classification of CNS tumors, these tumors are grouped together with granular cell tumors of the pituitary and pituicytomas as "most likely representing a spectrum of a single nosological entity" unified by all having expression of thyroid transcription factor 1 (TTF-1) 6. Having said that, they go on to describe distinctive histological features, as such we continue to discuss these two other entities separately.

Spindle cell oncocytomas are estimated to represent only 0.1 to 0.4% of all sellar tumors 2 and to occur more frequently in the 6th to 8th decades of life, with no gender preference 3.

As it happens with pituitary macroadenomas, spindle cell oncocytomas also commonly present with visual impairment, panhypopituitarism, and headaches 2,5

The histogenesis of this tumor remains unclear, with some authors inferring that it derives from the folliculostellate cells of the adenohypophysis 4.  

Microscopically, these tumors demonstrate bundles of spindle cells with eosinophilic and granular cytoplasm.

Immunohistochemistry is essential for their diagnosis, usually being positive for vimentin, S-100, EMA, galectin-3 and thyroid transcription factor 1 (TTF1) 2-3,5,6.  Electronic microscopy will show swollen mitochondria, a reduced number of lysosomes, and rough endoplasmic reticulum 5.

These tumors can be intrasellar, with or without a suprasellar component 2. Less frequently, they can invade the cavernous sinuses, destroy the sellar floor, and extend into the sphenoid sinus 2-4.

They have a richer blood supply than pituitary adenomas, such that intraoperative bleeding poses a greater risk.

Reported as having the appearance of a solid mass isodense to the brain parenchyma.

  • T1/T2
    • ​​isointense to the brain parenchyma on T1
    • linear flow voids: represent blood vessels
    • hypointense foci: thought to represent hemosiderin deposits 5
  • T1 C+ (Gd): intense heterogeneous early enhancement, in contradistinction to macroadenomas, which enhance more slowly and not as avidly 5

The surgical approach is done with a transsphenoidal resection. γ-knife treatment or radiotherapy can be considered for the recurrent cases 3. Post-treatment imaging follow-up is recommended as up to a third of the cases have been reported to recur 2

Roncaroli et al. first described the pituitary oncocytomas in 2002 1,2

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