Generalized Subcutaneous Emphysema Secondary to Pneumomediastinum in a Newborn kitten

Background: Pneumomediastinum is a rare entity characterized by the introduction of air into the mediastinum. Primary or spontaneous pneumomediastinum may occur in the absence of any disease whereas secondary pneumomediastinum may be due to a number of precipitating factors. The clinical picture is severe and the onset is acute. The present report describes the clinical presentation, treatment, and the findings of a forensic investigation of a case of generalized subcutaneous emphysema secundary to pneumomediastinum in a newborn kitten. Case: A newborn kitten was presented to a veterinary climic with a history of generalized air accumulation in the subcutaneous tissue of acute onset which was noted whenever the animal suckled. Clinical care and radiographic examination were performed. Radiographic findings included areas of radiolucency within the subcutis suggestive of generalized subcutaneous emphysema. In the thoracic cavity, there was ventral displacement of the thoracic trachea and increased radiolucency in the cranial mediastinum suggestive of pneumomediastinum. There was loss of definition of the cervical trachea suggestive of tracheal rupture. Based on the radiographic findings, the clinician decided to aspirate the air accumated within the subcutis using a needle and a syringe. However, this emphysema rapidly formed after the subcutaneous air was aspirated. Euthanasia was elected due to the poor prognosis and the animal was submitted for necropsy. Main gross findings included traumatic intercostal laceration adjacent to the lungs under the axilla and tracheal perforation. Tracheal perforation resulted in persistent air leakage from the trachea causing pneumomediastinum which evolved into generalized subcutaneous emphysema causing the animal to inflate as air became trapped within the subcutis imparting a blown up appearance to the cat. Microscopically pulmonary collapse was observed. Symptomatic treatment was instituted and consisted of puncturing the distended skin with needle and syringe. Percutaneous drainage of the subcutaneous air was unsuccessful.Discussion: In the present case, the diagnosis of generalized subcutaneous emphysema due to pneumomediastinum in a newborn kitten was based on the history, clinical signs, radiographic findings, and gross necropsy lesions. However, the histopathological findings were non-specific. The present case is an example of secondary pneumomediastinum. Tracheal perforation resulted in massive air penetration into the mediastinum. Generalized subcutaneous emphysema developed as a complication of the pneumomediastinum. Queens carry their offspring using their mouth. We suggest that the tracheal lesion is a penetrating tracheal trauma and that this injury was inflicted by the mother's canine teeth as she transported the kitten with the animal's neck and chest inside her mouth. There was no history that the kitten was attacked by other animal or of any other type of trauma. Initial conservative treatment consisted of puncturing the skin in order to release subcutaneous air and relieve pain. Oxygen supply was not considered due to practical reasons since such supportive therapy would worsen the clinical picture of the patient. Necropsy findings were of major importance to establish a definitive diagnosis. Gross lesions included tracheal perforation, which caused pneumomediastinum through air leakage into the mediastinum and lead to the subcutaneous emphysema. We conclude that unintentional traumatic injuries in a newborn kitten caused by the queen should be considered as a cause of pneumomediastinum and subcutaneous emphysema. The clinical picture is severe, of acute onset, and exhibits a rapidly progressive course.