Granular cell tumors of the pituitary region, also known as pituitary choristomas, are rare low-grade tumors of the posterior pituitary and infundibulum.
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Terminology
Care must be taken when reading older literature as granular cell tumors of the pituitary region, and alternative names including pituitary choristoma and Abrikossoff tumor, have in the past been thought to be, at least by some, equivalent to a pituicytoma.
In the 5th edition (2021) of the WHO classification of CNS tumors, these tumors are grouped together with pituicytomas and spindle cell oncocytomas of the pituitary gland as "most likely representing a spectrum of a single nosological entity" unified by all having expression of thyroid transcription factor 1 (TTF-1) 4. Having said that, they go on to describe distinctive histological features, as such we continue to discuss these two other entities separately.
Pathology
Microscopic appearance
Granular cell tumors of the pituitary are composed of sheets of densely packed large polyhedral cells, with abundant eosinophilic cytoplasm filled with periodic acid-Schiff–positive granules 1,2,4.
Immunophenotype
Immunohistochemistry shares some similarities to pituicytomas 3:
TTF1: positive nuclear staining
S100: positive
vimentin: positive
alpha-1-antitrypsin: positive
GFAP: usually negative
Radiographic features
Granular cell tumors of the pituitary region are usually located in the suprasellar region, having arisen from the infundibulum, or less frequently from the posterior pituitary and thus located with the sella 3. When small, they can be seen localized to the pituitary stalk 3.
CT
It appears hyperdense on non-contrast CT scans 5.
The occurrence of calcification may be influenced by the size of the lesion5.
MRI
The lesion is a well-defined, rounded mass situated retrochiasmatically.
Displays an isointense signal on T1-weighted images. Shows iso- or hypointense signals on T2-weighted images 5.
Some cases exhibit heterogeneous enhancement with contrast, others demonstrate a homogeneous enhancement pattern5.
Larger tumors generally do not lead to enlargement or destruction of the sella 5.
Differential diagnosis
When small, and clearly localized to the infundibulum the main differential includes:
pituicytoma and spindle cell oncocytomas of the pituitary gland (possibly all part of the same disease, see above)
When larger, then it is difficult to anticipate the diagnosis with other diagnoses being far more common, including:
-
pituitary infiltration
See also
granular cell tumor - general article
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