Subcutaneous chronic expanding haematomas in six dogs

Introduction: Chronic expanding haematoma (CEH) is a slowgrowing reactive lesion that can mimic soft tissue sarcoma (STS) and that is associated with trauma or surgery in man. CEH has been reported in dogs following injection or trauma. Materials and Methods: Six cases of canine CEH were examined. Anamnesis and follow-up were collected. Tissues were processed routinely and stained. Microscopical findings in canine CEH were evaluated and compared with three cases of injection-type panniculitis (ITP). Results: CEHs were located on the ischial tuberosity (2/6), flank (2/ 6), neck and shoulder and ranged from 3 to 20 cm in diameter. Histology revealed a central cavity, containing fibrin and erythrocytes, surrounded by a multilayered capsule composed of an internal band of immature granulation tissue, an intermediate layer of perpendicularly oriented vessels and an external fibrous layer infiltrating adjacent tissues. After surgery, three cases recurred and three had delayed healing. Three cases of ITP lacked prominent layering, had a thinner capsule and mild inflammation. Conclusions: CEH may represent an uncommon evolution of necrotizing panniculitis that can undergo post-surgical complications and, because of the infiltrative growth, may need to be differentiated from STS.