Skeletal-extraskeletal angiomatosis in a female Boxer puppy

A 3-month-old female Boxer puppy presented for bilateral inguinal lymph node enlargement, vulvar swelling and hip pain. Pelvic radiographs revealed moth-eaten to permeative lytic lesions affecting the right hemipelvis and right femoral head and neck. An incomplete pathological fracture of the cranial proximal right femur, an incomplete right femoral neck fracture and a suspected folding fracture of the right ischium were also noted. The dog was euthanized and submitted for necropsy. The fractures were confirmed at necropsy and were surrounded by extensive dark red areas in the skeletal muscle and subcutaneous tissues. Additional gross findings included dark red and enlarged inguinal and iliac lymph nodes, dark red foci in the lungs and a swollen vulva. Histology revealed an infiltrative proliferation of vascular channels lined by bland to mildly hypertrophied CD31-positive and variably PROX1-positive endothelial cells. Affected tissues included the right femur and ischial arch, adjacent gluteus medius muscle, multiple lymph nodes, lungs and reproductive tract. The findings are consistent with skeletal-extraskeletal angiomatosis, a rare proliferation of vascular structures involving both the bone and soft tissues. In children, this condition is thought to represent a vascular malformation. The few reports of this entity in dogs have all involved the distal phalanx and surrounding soft tissue with this case being, to the best of our knowledge, the first report in the femur and visceral organs.