NAVLE Practice Question - Other Small Mammal - multisystemic

NAVLE Practice Question — Other Small Mammal

A necropsy is performed on a 26-month-old male Sprague-Dawley rat that was euthanized due to progressive neurological signs including ataxia and head pressing. Gross examination reveals a large mass within the sella turcica compressing the overlying brain. Histopathology shows a tumor composed of uniform polygonal cells with pale cytoplasm that do not stain positively with standard acidophilic or basophilic dyes. What is the MOST likely diagnosis?

A. Chromophobe pituitary gland adenoma ✓

B. Pituitary acidophilic adenoma

C. Craniopharyngioma

D. Meningioma

E. Glioblastoma

———

Correct Answer: A. Chromophobe pituitary gland adenoma

Explanation:

Pituitary chromophobe adenoma is the correct answer. The histological description of cells that do not stain with standard acidophilic or basophilic dyes is characteristic of chromophobe adenomas. These are the most commonly classified type of pituitary tumors in rats histologically, though immunohistochemistry often reveals that many are actually prolactin-secreting (lactotroph) tumors.

The clinical presentation of progressive neurological signs including ataxia and head pressing in an aged rat with a sellar mass compressing brain tissue is consistent with a pituitary macroadenoma. Chromophobe adenomas typically arise from the pars distalis.

Option B (acidophilic adenoma) would show cells that stain with acidic dyes like eosin. Option C (craniopharyngioma) arises from Rathke's pouch remnants and has different histological features. Option D (meningioma) would arise from meninges and have characteristic whorling patterns. Option E (glioblastoma) arises from glial tissue and has different histological features including necrosis and vascular proliferation.

Image Source: Ask JPC case study showing pituitary adenoma with concurrent mammary fibroadenoma (https://www.askjpc.org/wsco/wsc_showcase2.php?id=K0JRTEJKcUMrTURFNC8xT1daK3JTdz09).

References: Percy DH, Barthold SW - Pituitary neoplasia in rats; Laboratory Animal Medicine 3rd ed - Endocrine neoplasms; Toxicol Pathol 43:145-170 - INHAND classification.

———

Get 10,000+ practice questions free at navleexam.com