Nonproliferative and Proliferative Lesions of the Rat and Mouse Endocrine System.

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) Project (www.toxpath.org/inhand.asp) is a joint initiative among the Societies of Toxicological Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in the endocrine organs (pituitary gland, pineal gland, thyroid gland, parathyroid glands, adrenal glands and pancreatic islets) of laboratory rats and mice, with color photomicrographs illustrating examples of the lesions. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous and aging lesions as well as lesions induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for endocrine lesions in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists.

Multiple atypical mucosal xanthomas in a dog similar to human verruciform xanthoma.

A case of atypical mucosal xanthomas in a 14-year-old Shi-Tzu dog is reported. Grossly, 1-6-mm granular plaques or slightly elevated papillary nodules were found in the oral cavity (dorsal and ventral sides of the tongue, inner upper lip) and in the upper digestive tract (esophagus, stomach). Microscopically, subepithelial aggregates of large foamy cells were found in strong association with papillary epithelial hyperplasia. By immunohistochemistry, the majority of these cells tested positive for lysozyme and ACM1. The cells had cytoplasmic lipid content that stained positively with oil red O. These findings confirmed a monocyte/macrophage lineage. On the basis of macroscopic observations, microscopic changes, and the absence of a clinical metabolic defect, the condition in this dog appears similar to that of humans with oral verruciform xanthoma. The pathogenesis of these xanthomas in the dog remains obscure, although this condition appears to affect people and dogs with an Asian origin.

Malignant spinal meningioma in a CD-1 mouse.

Spontaneous meningiomas are extremely rare tumors in small laboratory animals, except in some strains of rats and in the B6C3F1 mouse. We report the case of a male CD-1 mouse in poor health condition, with severe apathy and partial paresis of hindlegs. No macroscopic lesion was noticed at necropsy. Microscopic examination revealed the presence of a malignant meningioma (approximately 3mm in diameter) at the distal lumbar level of the spinal cord, invading the vertebral canal, and bilaterally the ventral and dorsal nerve roots and the dorsal root ganglia. The tumor displayed highly cellular sheets of polygonal cells with a well-delineated, abundant, eosinophilic cytoplasm and scarce fibrovascular stroma; epithelioid and sarcomatous areas were also present. The mitotic activity was moderate. Tumor cells expressed vimentin immunoreactivity and were negative for periodic acid-Schiff (PAS), silver impregnation for reticulin, chromogranin A, glial fibrillary acidic protein (GFAP), cytokeratin (CK) and S-100 protein. The diagnosis of malignant spinal meningioma was based on the morphologic features of the neoplasm, the evidence of local invasion and the immunohistochemical results.

Cerebral meningioangiomatosis in a CD-1 mouse: a case report and comparison with humans and dogs.

Meningioangiomatosis is a rare proliferative disorder of the central nervous system. Several cases have been described in humans, a few in dogs, one case in a cow and one in a horse; meningioangiomatosis has never been recorded in rodents. The pathogenesis of this condition remains obscure and it is uncertain whether it represents a neoplastic or malformative process. Meningioangiomatosis is usually characterized by a plaque-like leptomeningeal proliferation of mainly spindle-shaped cells and small blood vessels, extending along the Virchow-Robin spaces into the adjacent neural parenchyma. In this report, we presented a brain lesion displaying the histopathological key features of the meningioangiomatosis and involving the base of the cerebrum (fronto-basal area) and the brainstem, found in a male CD-1 mouse. The histopathological and immunohistochemical results are discussed, and compared with those previously reported in other cases of meningioangiomatosis.

A mammary gland adenomyoepithelioma in a C57BL/6 mouse.

Mammary gland adenomyoepitheliomas are benign complex mammary gland tumors composed of neoplastic cells of epithelial and myoepithelial origins, described in many species (humans, dogs, cats, rats) and rarely in mice. We report here an adenomyoepithelioma in a C57BL/6 female mouse. Histologically, tubes and cords formed by neoplastic epithelial cells were separated by bundles of neoplastic myoepithelial cells in a clear and partially mucinous matrix. The tumor displayed characteristics of a benign neoplastic proliferation with a compressive growth pattern, and moderate cellular pleomorphism and mitotic index. At immunohistochemistry, the epithelial cells were strongly cytokeratin positive; the myoepithelial cells were weakly cytokeratin positive and strongly smooth muscle actin positive. This is to our knowledge, the first report of a mammary gland adenomyoepithelioma in a C57BL/6 mouse.