Spontaneous Pneumothorax

Spontaneous pneumothorax is a condition observed in both dogs and cats and occurs when air enters the pleural (chest) cavity without any known history of trauma or accidental medical penetration of the chest wall. Under normal circumstances, the chest cavity maintains a negative pressure that keeps the lungs fully expanded. When this negative pressure is lost, air accumulates within the chest cavity, leading to partial or complete collapse of the lungs.

From an anatomical standpoint, there are two primary pathways through which air can enter the chest cavity and cause a spontaneous pneumothorax: the respiratory tract and the esophagus. The most common mechanism involves damage to lung tissue or the trachea, allowing inhaled air to escape into the pleural space and collect around the lungs. This type of lung compromise is most often caused by the presence of bullae or blebs located along the margins of the lung lobes. These structures are small, air-filled sacs that can rupture into the chest cavity (Figure 1).

In dogs, bullae and blebs are most frequently identified in patients without concurrent lung disease and represent the most common cause of spontaneous pneumothorax. In contrast, these lesions are less commonly identified in cats, where spontaneous pneumothorax is more often associated with underlying pulmonary disease.

Secondary Causes

The second pathway for air entry into the chest cavity involves perforation of the esophagus. This results not only in pneumothorax but also in the accumulation of air in other anatomical locations, such as beneath the skin (subcutaneous emphysema) and around the cardiac structures.

Additional secondary causes of spontaneous pneumothorax include:

Dogs

• Neoplasia (cancer)
• Bacterial pneumonia
• Pulmonary abscesses
• Fungal infections
• Heartworm disease
• Pulmonary thromboembolism
• Migration of grass awns

Cats

• Primary lung disease
• Inflammatory airway disease
• Heartworm infection
• Lungworm infestation
• Bronchopulmonary dysplasia
• Idiopathic (unknown cause)

Spontaneous pneumothorax most commonly affects large-breed, deep-chested dogs, with no apparent sex predisposition. Siberian Huskies and other Northern breeds are disproportionately represented. In cats, no consistent breed or anatomical predisposition has been identified.

Common clinical signs include:

Dogs

• Increased respiratory rate
• Coughing
• Anxiety or restlessness
• Bluish or darkened mucous membranes (cyanosis)
• A visibly over-expanded chest
• Orthopneic posture, characterized by extension of the neck and outward positioning of the elbows, adopted to improve airflow

Cats

• Respiratory distress with increased breathing rate and effort
• Coughing
• Sudden collapse
• Lethargy and decreased appetite
• Vomiting
• Hiding behavior

When a pet is presented to a primary care veterinarian, thoracic radiographs (chest x-rays) are typically the first diagnostic test performed to identify air within the chest cavity that lies outside the lungs (Figure 2). Radiography is highly accurate for confirming the presence of a pneumothorax; however, it rarely identifies the underlying cause. As a result, advanced imaging—most commonly computed tomography (CT)—is often required to further evaluate the lungs and surrounding structures (Figure 3).

An ACVS board-certified veterinary surgeon is best equipped to determine the most appropriate imaging modality and to interpret the findings in order to discuss potential causes and treatment options.

Treatment strategies depend on the severity of clinical signs. Immediate stabilization is critical, as spontaneous pneumothorax can be life-threatening due to impaired ventilation. An initial intervention commonly recommended by primary care veterinarians is thoracocentesis. This procedure involves inserting a small needle into the chest cavity to remove accumulated air, thereby allowing the lungs to re-expand and improving the pet’s ability to breathe. Although thoracocentesis does not correct the underlying cause, it is a potentially life-saving temporary measure.

Long-term treatment options are broadly categorized into medical and surgical management. The most appropriate approach depends on the cause of the pneumothorax. Your primary care veterinarian and ACVS board-certified veterinary surgeon will collaborate with you to determine the optimal treatment plan.

Medical management includes:

• Supplemental oxygen therapy
• Placement of a thoracostomy tube (chest tube)

Oxygen therapy is essential because lung collapse compromises oxygen delivery to the body. Supplemental oxygen helps maintain adequate tissue oxygenation. Thoracostomy tubes are hollow tubes inserted through the chest wall into the pleural cavity (Figure 4), allowing intermittent or continuous removal of air. This promotes lung expansion and improves oxygen delivery throughout the body. However, spontaneous pneumothorax is rarely manageable long-term with medical therapy alone, and surgical intervention is often required to eliminate the source of air leakage.

Surgical treatment typically involves removal of the affected lung lobe(s) through a lung lobectomy (Figure 5). Access to the chest cavity can be achieved using one of three approaches: minimally invasive thoracoscopy, median sternotomy (through the breastbone), or lateral thoracotomy (between the ribs). Each technique offers specific advantages depending on the underlying disease, the location of the affected lung tissue, and available surgical equipment. The ACVS board-certified veterinary surgeon will assess each case individually to recommend the most appropriate approach.

The long-term prognosis for dogs with spontaneous pneumothorax is excellent when surgical treatment successfully removes the source of air leakage. In cases where the underlying cause cannot be surgically corrected, prognosis varies depending on disease severity and extent. Recurrence rates are approximately 3% following surgical treatment but can be as high as 50% in pets managed without surgery. Mortality rates further emphasize the importance of surgical intervention, with reported mortality of approximately 12% in surgically treated cases compared to over 50% with medical management alone.

Outcome data in cats are more limited. Overall prognosis can still be favorable depending on the underlying cause and response to therapy. A 2012 study reported that 54% of cats survived to hospital discharge, with most managed medically. In cats with small-volume pneumothorax, conservative treatment may result in good outcomes, although surgery may be necessary in severe or persistent cases. Consultation with an ACVS board-certified veterinary surgeon is recommended to determine the best course of action for each individual patient.