Thymic hematoma in juvenile dogs associated with anticoagulant rodenticide toxicosis.

Ten cases of thymic hematoma in young dogs (9-24 weeks of age) were reviewed. Anticoagulant rodenticide toxicosis was confirmed in 5 cases. Histologically, hemorrhage caused variable expansion of thymic lobules and interlobular septa. The medulla appeared to be the primary site of hemorrhage. In areas of severe hemorrhage, normal lobular architecture was lost and lymphocytes were admixed in the hemorrhagic exudate. Vasculitis, necrosis of capillaries, and degeneration of the capsule were observed in infarcted areas. In 2 cases, angiofibroplasia indicated a longer interval between onset of thymic hemorrhage and death. The lesions are similar to those in 5 cases of idiopathic thymic hemorrhage. Appropriate samples were not available for anticoagulant rodenticide analysis in 3 of these 5 idiopathic cases. Lesions in confirmed cases of anticoagulant rodenticide toxicosis also are compatible with published descriptions of idiopathic and spontaneous thymic hemorrhage, but are inconsistent with normal thymic involution. Analysis for anticoagulant rodenticides is indicated in cases of thymic hematoma when an obvious cause is not detected at necropsy.