A suspected canine lung variation: misleading patterns vs. powerful imaging and dissection tools

The lungs were divided into lobes based to the branching pattern of the principal bronchus. In the dog, the left and right lung have a cranial and a caudal lobe. In addition, the right lung possesses a middle and an accessory lobe. During the study of the canine thoracic cavity, we observed an unusual lung morphology and suspected an anatomical variation. In 2022, we dissected 20 formalin-fixed carnivores during the gross anatomy course at the Faculty of Veterinary Medicine of the University of Zagreb. One adult female, middle-sized crossbreed dog showed unusual lung morphology. These lungs were eviscerated, photographed and gross morphology was described. X-rays and CT scans were taken prior to the injection of silicon into the lumen of the bronchial tree. The pulmonary parenchyma was dissected and a silicon cast of the bronchial tree was produced. Bilaterally, the lungs appeared to lack the typical canine lobation due to poorly expressed interlobar fissures and fused interlobar surfaces. However, lobar margins were clearly visible under the pulmonary pleura. Along the dorsal edge, short interlobar fissures were expressed between the cranial and caudal lobe of both sides leading towards small interlobar surfaces only approximately 3 cm in size. Ventrally to these interlobar surfaces small pocket-like structures were developed. X-rays and CT scans showed a standard pulmonary structure. During dissection, the interlobar surfaces separated after firm pressure onto the pulmonary parenchyma. The silicon cast of the bronchial tree showed a typical canine branching. In the studied dog, we suspected that the pulmonary pleura covered interlobar fissures and fused the lobes giving the impression of only one lobe developed per lung. However, imaging techniques, dissection and casting proved a typical canine lobation and a standard branching of the bronchial tree. We speculate that the extreme fusion of interlobar surfaces was due to postmortal changes and the conservation process ; however, we cannot exclude any pathological causes. Since 1967, our department is involved in studies of anatomical variations (1, 2, 3) in order to contribute to the clinical knowledge, which is required for accurate interpretation of imaging techniques and during surgical procedures.