Severe idiopathic thymic hemorrhage in two littermate dogs.

Two 6-month-old littermate Shetland Sheepdogs were found to have severe thymic hemorrhage unassociated with trauma or poisoning. One dog survived the insult with supportive care, and the other died and was necropsied. Antemortem laboratory data and radiographic findings for both dogs were consistent with acute blood loss into the mediastinum. Hemorrhage was restricted to the thymus and mediastinum in both dogs.