Pulmonary fibrosis (PF) is defined as a gradual, interstitial fibrous disease of the lung parenchyma. PF causes collapse of the lung lobe, which can lead to lung lobe torsion of the other side. A 14-year-old male Pekinese dog was referred to the Veterinary Medical Center, Chungbuk National University. The chief complaint was acute dyspnea. The dog had a history of chronic cough, which lasted for 18 months, and the cough had recently deteriorated. Tachypnea was observed on physical examination. As a result of thoracic radiographs, ultrasonography, and computed tomography, lung lobe torsion and collapse were diagnosed. A postmortem examination revealed lung lobe torsion of the left cranial lobe and carnification of the right cranial lobe. Histologically, severe and diffuse interstitial fibrosis with distortion of alveolar architecture and severe congestion and/or hemorrhage were observed in the right cranial lobe and left cranial lobe, respectively. Although the cause of pulmonary fibrosis was undetermined, this case showed a typical lung lobe torsion caused by pulmonary fibrosis.

Canine heartworm disease is typically characterized by the presence of heartworms in the pulmonary artery and, to a lesser degree, the right ventricle. Systemic arterial dirofilariasis is an unusual manifestation of heartworm disease of dogs that results from aberrant migration of Dirofilaria immitis into the peripheral arterial circulation. A three-year-old Jindo dog was referred to the Veterinary Medical Center because of hindlimb lameness, paresthesia of hindlimbs, and interdigital ischemic necrosis. Angiography and ultrasonography were performed, resulting in diagnosis of heartworm infestation. In necropsy, entangled heartworms were present throughout the body, including lungs, kidney, small intestinal lumen, and arteries, in addition to the right ventricle and pulmonary artery. Histologically, lung showed adult heart worms in vessels, organized thrombotic vessels, and interstitial pneumonia featuring type II pneumocyte hyperplasia, thickened alveolar wall, and compressed alveolar spaces. Chronic parenchymal lesions, such as focal or diffuse necrosis, fibrosis, and dystrophic calcification were remarkable in liver and kidney. The current case showed a typical canine systemic heartworm disease caused by aberrant migration of Dirofilaria immitis.