Pulmonary vascular sclerosis in an albino rat with leukemia

The animal investigated was a two years old male control Sprague-Dawley rat which died spontaneously during a carcinogenicity study. Post-mortem exami nation disclosed hepatic and splenic enlargement. At microscopical examinat ion, massive leucaemic infiltration was observed in many tissues/organs, in cluding bone marrow spleen, liver and renal blood vessels. A very unusual f inding was observed in the lung, consisting of scattered micronodules which replaced most of the lung parenchyma. They contained collagen, displaying a somewhat circular distribution at the periphery of the lesions, fibrin, l eukemic cells and fibroblasts. Immunostaining for desmin revealed the presence of smooth muscle fibers wit hin the nodules, while staining for elastic fibers showed clearly that the internal and external elastic membranes were identifiable within the nodule s. The diagnosis of pulmonary vascular sclerosis was made on the basis of m icroscopical and immunohistochemical findings.