granular cell tumour of the pituitary

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Granular cell tumor of the pituitary region, also known as a pituitary choristoma, are rare low-grade tumors of the posterior pituitary and infundibulum.

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, but in fact represent a histologically separate entity, recognized in the current (2016) WHO classification of CNS tumors .

Pathology

Microscopic appearance

Granular cell tumors of the pituitary are composed of sheets of large polyhedral cells, with abundant eosinophilic cytoplasm filled with periodic acid-Schiff–positive granules . They have only focal spindled areas (in contrast to pituicytomas). They are usually negative for GFAP .

Immunophenotype

Immunohistochemistry shares some similarities to pituicytomas :

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 . When small, they can be seen localized to the pituitary stalk .

CT

Granular cell tumors of the pituitary region are usually not calcified .

MRI

Heterogeneous signal mass with variable contrast enhancement .

Differential diagnosis

When small, and clearly localized to the infundibulum the main differential includes:

When larger, then it is difficult to anticipate the diagnosis with other diagnoses being far more common, including:

pituitary macroadenoma
meningioma
pituitary metastasis
pituitary infiltration
- lymphocytic hypophysitis
- neurosarcoidosis
optic pathway glioma