Spontaneous Pituitary Neoplasm in Two Female Geriatric Southern Giant Pouched Rats (Cricetomys ansorgei)

Abstract

Southern giant pouched rats (Cricetomys ansorgei) are a small muroid species native to the sub-Saharan Africa. Their exceptionally developed olfactory system, trainability, and relatively small size makes them useful working animals for various applications in humanitarian work. At our institution, a breeding colony of Southern giant pouched rats is maintained to study their physiology and utility as scent detectors. This case report describes the occurrence of spontaneous pituitary neoplasms with distinct clinical presentations in 2 geriatric (approximately 7.5 y old) wild-caught female Southern giant pouched rats. The first pouched rat displayed vestibular deficits, including left-sided head tilt, ataxia, disorientation, and circling. MRI revealed a large, focal heterogeneous mass arising from the pituitary fossa. The second pouched rat presented with polyuria, polydipsia, and hyperglycemia but no neurologic signs. Examination after euthanasia revealed a prolactin (PRL)-expressing pituitary carcinoma and adenoma in the first and second pouched rat, respectively, associated with mammary hyperplasia in both animals. This is the first report of spontaneous PRL-producing pituitary tumors in Southern giant pouched rats.

Figure 1.

Restraint of African pouched rats for nonsedated blood draws. (A) African pouched rats are restrained with minimal contact beneath a standard size rat cage and distracted with high value treats. (B) A cut-out edge of the cage allows easy handling and blood draw in the conscious animal.

Figure 2.

Representative MRI images of the head of case 1. (A) In the T2-weighted fast spin echo (FSE) sagittal (SAG) image of the head, a mass was identified (outlined with white arrows). (B) Serial transverse sections of T2-weighted FSE images of the head from cranial (top left, i) to caudal (bottom right, vi), the mass first appears in image i) mass and is outlined by white arrows in ii) to vi).

Figure 3.

Representative gross and histopathologic images of the pituitary neoplasm of case 1 and case 2. (A) Transverse section of the skull with brain and pituitary gland in situ. Scale bar: 1.0 cm. An ovoid, expansile mass (arrows) compresses and elevates the overlying brain (case 1). (B) Skull with brain and pituitary gland, hematoxylin and eosin (H&E). Scale bar: 1.0 cm. The mass (arrows) is densely cellular and has a variegated appearance imparted by congested intratumoral sinusoids. Neoplastic cells invade the underlying basosphenoid bone (square) (case 1). (C) Detail of the neoplastic cells, H&E. Scale bar: 100 μm. Tightly arranged cords of polygonal cells amid delicate fibrovascular stroma surround congested intratumoral capillaries and sinusoids (case 1). (D) Neoplastic cells with strong cytoplasmic immunolabeling for prolactin (PRL). Scale bar: 100 μm. (E) Transverse section of brain and pituitary gland. Scale bar: 0.5 cm. A compressive, solid plaque-like mass (arrows) arises from the region of the pituitary gland and elevates the overlying thalamus. Scale bar: 100 μm (case 2). (F) Brain and pituitary gland, H&E. Scale bar: 0.5 cm. On light microscopy, the mass (arrows) appears densely cellular and noninvasive (case 2). (G) Detail of neoplastic cells, H&E. Scale bar: 100 μm. Neoplastic cells form packets and trabeculae of plump polygonal cells often bearing a single intracytoplasmic macrovacuole and surrounding congested capillary and sinusoids (case 2). (H) Neoplastic cells have strong cytoplasmic immunolabeling for PRL. Scale bar: 100 μm.