International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Dog

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the societies of toxicologic 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 lesions observed in most tissues and organs from the dog used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. 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 lesions, lesions induced by exposure to test materials, and relevant infectious and parasitic lesions. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

Characterization of Spontaneous Vascular Findings in the Papillary Muscles of Beagle Dogs

Standard histology trimming practices for toxicity studies in dogs include preparation of a section of the papillary muscle associated with the left ventricular free wall-the anteriolateral or anterior muscle. In contrast, the posteromedial or posterior papillary muscle, associated with the interventricular septum, is not commonly evaluated. In humans, the posterior papillary muscle is more often affected in ischemic myocardial disease, in large part due to the absence of collateral circulation, in contrast to the anterior muscle. Due to the differential vascular supply to the papillary muscles, we sought to determine whether there is a higher incidence of spontaneous coronary vascular changes in the posterior papillary muscle versus the anterior muscle in dogs. The hearts of 30 vehicle-treated or untreated beagle dogs that were euthanized for other purposes were collected and sectioned in a consistent manner to include both papillary muscles for histologic evaluation. The posterior muscle consistently had higher incidences of intramural coronary arteries affected by vascular medial hypertrophy, medial arteriosclerosis, intimal hyperplasia, and/or disruption or loss of the internal elastic lamina. This observation may have significant implications for the evaluation and characterization of spontaneous and xenobiotic-induced cardiovascular lesions in dogs.

Bovine cardiac mesothelial hyperplasia: a common incidental finding in adult cattle

Cardiac mesothelial hyperplasia forming pale plaque lesions on the epicardial surface is a common incidental finding in the hearts of aged humans. A similar phenomenon with a more papillary appearance has also been reported as an incidental finding in dogs and mice. These lesions are believed to occur in response to friction between the epicardium and overlying pericardium. We investigated this lesion in adult cattle, a phenomenon that has been associated with bovine leukemia virus infection and epicardial lymphoma. We examined 73 hearts from adult cattle, predominantly of dairy breeds: 53 from a rendering facility and 20 from a state diagnostic laboratory. Cardiac mesothelial hyperplasia was much more prevalent in cattle than in other reported species (97% of examined hearts). The most common distribution was overlying the great vessels in a dark red papillary pattern. Cardiac mesothelial hyperplasia was also variably observed on all 4 cardiac chambers and the pericardium. Occasionally these lesions took on a smooth plaque-like appearance resembling those observed in humans. The lesions varied from 0.25 cm² to covering 90% of the epicardial surface. No association was observed between cardiac mesothelial hyperplasia and bovine leukemia virus infection or cardiac lymphoma. Cardiac mesothelial hyperplasia was a common incidental finding in bovine hearts that must be distinguished from neoplasia and acute or chronic inflammation.

Cardiac mesothelial papillary hyperplasia in four dogs

Mesothelial papillary hyperplasia (MPH) has been described as an incidental finding on the epicardial surface of clinically normal laboratory Beagle dogs. We describe MPH in 4 dogs diagnosed with acute cardiac tamponade (1 case) or chronic cardiac disease (3 cases). Cardiac MPH appeared as distinct, soft, irregular villous plaques on the epicardial surface of the auricles and occasionally the ventricles. Histologically, areas of MPH were composed of multiple papillary fronds arising from the epicardial surface and projecting into the pericardial space. Fronds were covered by cuboidal and occasionally vacuolated mesothelial cells and were supported by loose fibrovascular stroma with various degrees of edema and inflammation. Although these may represent incidental findings with no clinical significance, the gross appearance warrants differentiation from other conditions. Additional insight into the pathogenesis of MPH is needed to fully understand its significance in the face of concurrent cardiac disease.

Characterizing “Adversity” of Pathology Findings in Nonclinical Toxicity Studies

The identification of adverse health effects has a central role in the development and risk/safety assessment of chemical entities and pharmaceuticals. There is currently a need for better alignment regarding how nonclinical adversity is determined and characterized. The European Society of Toxicologic Pathology (ESTP) therefore coordinated a workshop to review available definitions of adversity, weigh determining and qualifying factors of adversity based on case examples, and recommend a practical approach to define and characterize adversity in toxicology reports, to serve as a valuable prerequisite for future organ- or lesion-specific workshops planned by the ESTP.