few day history of hyporexia and vomiting
On initial examination, the large volume of gas gave the false impression of free peritoneal gas as could occur secondary to gastric perforation and necessitating emergent surgical intervention. However, the lack of peritoneal effusion or diffuse peritonitis was incongruent with a gastrointestinal perforation, prompting more close evaluation of the location of the gas artifact. Given the now suspected SQ gas and the pleural abnormalities, thoracic radiographs were recommended (radiographs 1-2).
Lateral thoracic radiograph of this patient, after the abdominal ultrasound exam
Ventrodorsal radiograph of this patient, after the abdominal ultrasound exam
The thoracic radiographs revealed a moderate volume of subcutaneous emphysema, cervical intrafascial gas, pneumomediastinum, pneumoretroperitoneum, and a small volume of pneumothorax. Tracheal laceration secondary to venipuncture or unreported trauma were primary considerations for this large volume of gas, but no underlying cause was determined in this patient. The possibility that the pneumomediastinum was secondary to vomiting was considered, though the clinical signs were not reportedly that severe.
Ultimately, although striking, the changes to the mediastinum, pleural space, etc were considered unrelated to the initial presenting complaining of gastrointestinal signs, though may have contributed to the progressive decline in the patient’s status. Because no prior radiographs were available to review, the possibility of previous pulmonary or mediastinal pathology could not be ruled out.
Over the course of several days, the patient responded well to continued empiric medical management for enteritis/typhlitis and the volume of thoracic gas continued to decline. The patient was discharged and lost to follow-up.
The feline mediastinum divides the thorax into two halves and communicates with both the retroperitoneal space caudally, and the cervical fascia cranially. In veterinary literature, most cases of pneumomediastinum are secondary to an obvious inciting pathologic event. In cats, pneumomediastinum has been described secondary to endotracheal intubation, trauma, neoplasia (pulmonary carcinoma), viral infections (necrotizing bronchopneumopathy), and endoscopy. The authors are unaware of current veterinary literature describing spontaneous pneumomediastinum alone in cats. A human study that was done using cats revealed overdistention and rupture of alveoli could cause subsequent air leaking into the pulmonary interstitium. This led to dissection along the bronchovesicular interface with the mediastinum. This phenomenon is known as the Macklin Effect and has been described as a source of pneumomediastinum. Treatment of pneumomediastinum with or without concurrent pneumothorax may include supplemental oxygen therapy if needed, analgesics and correction of the underlying cause, if determined. Prognosis is excellent depending on the severity/etiology with an 87% survival reported in a retrospective of 45 cases of pneumomediastinum in a cat.
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