Acquired Diaphragmatic Eventration in a Dog

Abstract

Background: Diaphragmatic eventration is characterized by weakness of the diaphragmatic muscle, which leads to cranial dislocation of the affected diaphragm and, ultimately, in dyspnea. This condition is rare in humans and even rarer in animals, and may be congenital or acquired. The acquired form is less commom and may be induced by trauma or inflammation and neoplastic invasion of the phrenic nerve. Here, we report a case of acquired diaphragmatic eventration in a dog, with the aim of increasing the knowledge of this condition in animals and helping others to recognize and treat future cases.Case: A 12-year-old male dachshund presented with severe dyspnea, exercise intolerance and episodes of coughing. Based on a physical examination and imaging, the main suspicion was a diaphragmatic hernia, and surgery was performed. When the surgeon entered the thoracic cavity, an extremely thin - yet, intact - right hemidiaphragm was observed. The left side of the diaphragm was normal. A polypropylene mesh was sutured to the affected diaphragm in an attempt to strengthen the hemidiaphragmatic muscles and prevent further insinuations of viscera into the thoracic cavity. The dog developed bronchopneumonia, postoperatively, and was hospitalized and treated with antibiotics, analgesics and support medication. However, the dog died five days after surgery. A postmortem examination revealed that the right side of the diaphragm was markedly thin and flaccid. Diaphragm samples were collected for histopathological examination. For comparison, a sample of normal diaphragm was collected from a same age, matched dachshund that died due to an unrelated condition. This tissue was called “diaphragm control”, and it was collected in order to compare the histologic features of a normal diaphragm muscle with the affected one. Histopathology revealed a marked reduction of muscle fibers. In the affected sample, replacement of these fibers by fibrous connective tissue and a marked infiltration of fat were seen among the remaining muscle fibers. Multifocal areas of necrosis were also observed affecting some muscles fibers. Microscopic comparisons of both diaphragm samples (affected vs. control) revealed a drastic difference in the amount of muscle fibers and fat, corroborating the intense diaphragmatic atrophy observed in the diaphragm from the affected dog. Based on clinical presentation, the gross lesions observed during surgery and later during the post mortem examination, and histopathological findings, a definitive diagnosis of acquired diaphragmatic eventration was established.Discussion: Diaphragmatic eventration is rarely reported in small animal clinics and thus may be confused with other conditions. It must be mainly differentiated from diaphragmatic hernia and should be considered as a differential diagnosis when an animal, regardless of age, presents with dyspnea, apathy and coughing episodes. On suspecting diaphragmatic eventration, surgical intervention should be carried out as soon as possible. The recommended treatment is plication of the affected hemidiaphragm. However, in the present case, a polypropylene mesh was sutured to the affected area to support the atrophic muscles. It is thought that, trauma injured the dog’s phrenic nerve, affecting right hemidiaphragmatic innervation, and generating progressive atrophy of diaphragmatic muscle fibers. Subsequently, the dog developed diaphragmatic eventration due to diaphragmatic fragility. Diaphragmatic eventration is a very rare disorder in small animals and can be difficult to diagnose based solely on physical and radiographic examinations.