NQ-087 Answer: (B) Pituitary adenoma with oncocytic changes (pituitary oncocytoma)

Normal histology of pituitary: Before we look at the pathology of this case, let us look at histology of normal anterior pituitary gland. In brief, the normal anterior pituitary gland is composed of nests of epithelial cells that contain the basophils, chromophobes, and eosinophils. Basophils are the least common and the distribution is more restricted. Chromophobe is the most common and a small number of eosinophils (arrow) are usually scattered in between. In small biopsies, the nested architecture can be difficult to be recognized. The presence of occasional eosihophils among chromophobes is a useful hint in recognizing non-neoplastic anterior pituitary from pituitary adenoma. [Click here to see the image of a normal pituitary gland]

Pathology of the case: On hematoxylin and eosin stain, the nested architecture is lost. The cells have brightly eosinophilic granular cytoplasm and there are gaps in between the cells (the granular part is not very well shown on this image). The overall features are consistent with that of a neoplastic proliferation. The nuclei are slightly enlarged and with distinct nucleoli. These features, with the anatomical location taken into consideration, are most consistent with a pituitary adenoma with oncocytic changes also known as pituitary oncocytoma. Pituitary adenoma with oncocytic changes are strongly positive for synaptophysin. It is a neuroendocrine tumor arising from the anterior pituitary. Immunohistochemistry for hormone may not help to recognized these tumors as pituitary adenomas with oncocytic changes often are null tumors and do not produce any hormone. The positive synaptophysin separate oncocytic pituitary adenoma from oncocytic pituicytomas (granular cell tumor, oncocytic spindle cell tumor, and pituicytoma of the posterior pituitary).

 

The oncocytic change is resulted from the presence of substantial amount of mitochondria (white arrow) that is present in the cytoplasm.