Computed Tomographic and Clinical Findings in Domestic Rabbits (Oryctolagus cuniculus domesticus) with Pulmonary Emphysema.

Pulmonary emphysema (PE) is a poorly understood condition in rabbits. This retrospective case-control study investigated the CT and clinical findings of rabbits with PE. Institutional archive review identified 724 thoracic CT studies of 529 rabbits, including 76 PE-positive studies of 59/529 rabbits. Twenty-five PE-negative cases were selected randomly as a control group. The mean age of affected rabbits was 9 years (range 5-13 years). Cranial lung lobes were more commonly affected (p < .01). The X-ray attenuation in Hounsfield units (HU) of the emphysematous lung areas (median -905 HU) was significantly lower than in nonemphysematous lung lobes of the case (median -667 HU) and control group (median -652 HU). There was significantly lower X-ray attenuation in peripheral and bullous emphysema than in diffuse emphysema. There was no statistical correlation between clinical lower respiratory signs and PE presence. However, the small portion (n = 6, 10.2%) of affected rabbits with severe respiratory signs, such as open-mouth breathing and cyanotic mucous membranes, all had advanced PE and poor outcome. Secondary changes attributable to PE included pathologic rib fractures in 3 (5.1%) and bulla rupture leading to pneumothorax in 2 (3.4%) rabbits. Of the 15 rabbits with repeat examinations, PE was progressive in 12 (80%) and static in 3 (20%). PE is a common condition in rabbits that is readily detectable with CT. The progressive nature of PE should be considered when detected in asymptomatic rabbits. In rabbits with severe lower respiratory signs, PE should be considered as a potential cause.