Spontaneous pneumothorax occurs when atmospheric air enters the chest cavity with no clinical history of trauma or iatrogenic penetration into the chest cavity. Normally, there is a physiologic negative pressure within the chest that is responsible for maintaining inflation of the lungs. When this is lost, air will accumulate within the thorax and subsequent collapse of the lungs occurs. Anatomically there are two primary routes of entry of atmospheric air into the chest resulting in a spontaneous pneumothorax: the airways and the esophagus. The first occurs when there is compromise of lung or tracheal tissue resulting in inhaled air escaping into the chest cavity and accumulating around the lungs. Compromised lung tissue leading to a spontaneous pneumothorax is often caused by bullae or bleb formation at the edges of the lung lobes. These are small air filled sacs that can rupture within the chest cavity. Bullae and blebs are most commonly found in dogs with no concurrent lung disease and is the most common cause of spontaneous pneumothorax (Figure 1).
The second route of entry into the chest is from esophageal perforation that results in both a pneumothorax and additional air accumulation in secondary anatomic locations (i.e. under the skin and around the structures of the heart). Secondary causes of spontaneous pneumothorax include:
- Bacterial pneumonia
- Pulmonary abscess
- Fungal infection
- Heartworm disease
- Pulmonary thromboembolism
Spontaneous pneumothorax occurs primarily in larger dogs with no sex predilection. Siberian Husky dogs are overrepresented. Common clinical signs include:
- Increased respiratory rate
- Dusky blue mucous membranes (gums)
- Overinflated chest
- “Orthopneic” posture – this occurs in an attempt to open the airways and includes stretching of the neck and outward positioning of the elbows
When presenting your pet to your primary care veterinarian they will most likely recommend chest X-rays to look for air within the chest cavity not contained within the lungs (Figure 2). This diagnostic test is very accurate for diagnosing the presence of a pneumothorax. However, it rarely confirms the underlying cause and additional advanced imaging such as a CAT scan often becomes necessary (Figure 3). An ACVS board-certified veterinary surgeon will be able to determine the most appropriate imaging modality and discuss potential causes and treatments after reviewing the images.
Long-term outcomes for spontaneous pneumothorax are excellent with surgical intervention and removal of the inciting cause of the air leakage. Some causes of the air leakage are not amenable to surgical resection and those pet’s prognoses vary depending on the severity and extent of the disease. Recurrence rates of spontaneous pneumothorax are approximately 3% with surgical treatment, and as high as 50% without surgical treatment. Mortality rates reflect the necessity of appropriate surgical management, as there is a 12% mortality rate with surgery and over 50% with medical management alone.