While pneumothorax can be caused by trauma, the most common causes of spontaneous pneumothorax in dogs include neoplasia, heartworm infection, lung abscesses, pulmonary thromboembolism, congenital lobar emphysema, grass awn migration, bacterial pneumonia, parasitic or mycotic granuloma, and uremic pneumonitis. In this retrospective study, medical records of 303 cases of feline pneumothorax were identified: 155 resulted from trauma, 118 occurred postthoracentesis, and 35 were considered spontaneous, for which the most common sign was acute onset of respiratory distress. Ten cats had a history of cough and 4 were found collapsed. All cats had increased respiratory rate and effort. Abnormal lung sounds were present in 22 cats; 9 had harsh or increased bronchovesicular sounds, and lung sounds were absent in 5 cats. Diagnosis was made via radiography; pneumothorax was bilateral in 23 cats and unilateral in 7. Five underlying diseases were found in 21 cats: inflammatory airway disease (n = 9), neoplasia (n = 5), heartworm disease (n = 3), pulmonary abscess (n = 3), and lungworm disease (n = 1). Nineteen cats were discharged, 4 died, and 12 were euthanized. Treatments varied and included 16 managed with observation, 12 with thoracentesis, 2 with indwelling thoracostomy tubes, and 5 with surgical intervention.

Commentary
Whereas superior outcome of surgical management in canine spontaneous pneumothorax has been demonstrated, this study suggested that nonsurgical treatment can be successful in feline spontaneous pneumothorax. The decision to manage any disease with medical or surgical therapies should be based on scientific evidence. The underlying cause of pneumothorax in cats is often undetermined, and no clear recommendations can be made on the need for surgical therapy. Thoracentesis should be considered for cats with pneumothorax in order to improve respiratory effort. If negative pressure cannot be obtained during thoracentesis, or if pneumothorax returns shortly after completion, thoracostomy tubes should be used. If pneumothorax does not resolve, surgical exploration of the thorax may be warranted.—JD Foster, VMD

Source
Spontaneous pneumothorax in 35 cats (2001-2010). Mooney ET, Rozanski EA, King RG, Sharp CR. J FELINE MED SURG 14:384-391, 2012.