Pneumothorax in a dog infected with Dirofilaria immitis.

Rupture of a pulmonary abscess secondary to Dirofilaria immitis infection was the cause of acute pneumothorax in a dog. The dog was euthanatized because it did not respond well to treatment for pneumothorax. Postmortem examination revealed a mass in the right middle lung lobe and adult D immitis in the pulmonary artery. Histologic examination of the lungs revealed microfilariae, suppurative inflammation, thrombi, vasculitis, and fibrosis. Clinicians should include D immitis infection in the differential diagnosis of pneumothorax.