Spontaneous pneumothorax in a dog with interstitial pulmonary fibrosis and ruptured bullae

Canine interstitial pulmonary fibrosis has been described in dogs, almost exclusively in terrier breeds. Here, we present a unique case of spontaneous pneumothorax in a Labrador Retriever that was presented to an emergency clinic in severe respiratory distress. Despite resuscitation efforts, the animal died and was submitted for autopsy, which revealed severely collapsed lungs bilaterally and bullae along the pleural surface, with at least one ruptured bulla observed grossly. Histopathology of the lung revealed coalescing areas of interstitial fibrosis throughout most of the lung tissue examined. A pan-herpesvirus PCR assay was negative on fresh lung tissue. Based on our findings, we propose that the fibrosis and bullae developed sequentially, and the fibrotic interstitium likely decreased the elasticity in the respective alveoli, leading to increased alveolar wall tension in normal alveoli, which caused the formation of bullae. Our case adds to the body of literature regarding canine interstitial lung disease by describing a unique presentation of canine idiopathic interstitial fibrosis in a non-terrier breed.