Pituicytoma in a mouse.

* Address correspondence to: Daniel Morton, Abbott Laboratories, D-469 AP13A, 100 Abbott Park Road, Abbott Park, Illinois 600643500; email: [email protected]. A 26-mo-old female Crl:CD-l@(ICR)BR mouse in good general health was euthanized at the end of a study. At necropsy, a single cyst 5 mm in diameter was found in the left ovary, and multiple 2-4-mm cysts were seen in the endometrium. No gross abnormalities were detected in the brain or pituitary. All organs were fixed in 10% neutral buffered formalin, processed routinely, embedded in paraffin, sectioned at approximately 5 ~,m, and stained with hematoxylin and eosin. Sections of pituitary were later stained with phosphotungstic acid hematoxylin stain and for glial fibrillary acidic protein (GFAP) using rabbit polyclonal anti-GFAP (Zymed Laboratories, Inc., South San Francisco, CA) as a primary antibody and the avidinbiotin peroxidase method. Microscopically, an unencapsulated mass replaced the pars nervosa of the pituitary and infiltrated laterally along the dorsal and ventral surfaces of the pituitary and into the pars intermedia (Fig. 1). Closely packed small cells arranged in sheets had inapparent cytoplasmic borders; elongated, irregular nuclei; and eosinophilic, foamy to vacuolated cytoplasm (Fig. 2). Neoplastic cells surrounded several hypocellular, eosinophilic foci up to 100 )JLm wide that resembled normal neuropil. Nuclei measured approximately 10-15 Rm in length, had stippled to finely granular chromatin, and contained 1 to 3 small nucleoli. Nuclei occasionally were indented, flattened, or angular. In some areas, there was nuclear palisading. Mitotic activity was not observed. In some clusters of neoplastic cells, tangled filamentous structures that stained positively for GFAP were present between nuclei. Some neoplastic cells contained cytoplasmic granules that stained positively with phosphotungstic acid hematoxylin, but this stain did not demonstrate fibrillary processes typical of astrocytes. The absence of neoplastic tissue in the ventral hypothalamus adjacent to the pituitary stalk indicated that the neoplasm originated in the pituitary. Nerve roots