Lung Lobe Torsion:
Unlike humans, dogs and cats have separate lung lobes, which make them more prone to undergoing torsion (twisting). There are four right lung lobes and three left lung lobes. An artery, vein and air tube (bronchus) enter the base of the lung lobe adjacent to the heart. This is the most common location for the lobe to become torsed. Some lung lobes have well developed ligaments that suspend them within the chest cavity, and this helps to prevent these lobes from being torsed.

Once the lung lobe twists at its base, the vein collapses and does not allow blood to leave the lung lobe. Because the artery has much higher blood pressure and has a muscular wall, blood continues to flow into the lung lobe. As a result, the lung becomes congested with blood and the lobe weeps fluid into the chest cavity. As fluid accumulates in the chest, the normal lung lobes collapse, and the patient develops shortness of breath. In addition, the torsed lung lobe dies, which results in the release of toxins into the body.

The cause of lung lobe torsion is frequently not known; however, some dogs have an underlying cause such as cancer or chylothorax (fluid accumulation in the chest due to leaky lymphatic vessels).

Signs and diagnosis:
Breeds at higher risk for lung lobe torsion include deep-chested dogs such as Borzois and Afghans. Other susceptible breeds include the miniature poodle, dachshund, Shih Tzu, Yorkshire terrier, Pekingese and pug. Cats rarely develop this condition. The most common presenting signs of lung lobe torsion are shortness of breath (rapid, shallow breathing) and lethargy. Other warning signs of this condition include inappetance, vomiting and exercise intolerance.

The diagnosis of lung lobe torsion is based on clinical signs, physical examination, chest X-ray findings, and analysis of the fluid from the chest cavity. The chest fluid is typically blood-tinged but in some cases may appear very bloody. Other tests that may be indicated to help diagnose the problem include bronchoscopy (camera placed down the airways via the mouth), chest CT scan, and thoracoscopy (camera placed through the chest wall).

Surgery is recommended to remove the torsed lung lobe. This is typically performed via an incision that is made on the side of the chest. After the lung lobe is removed, a tube is placed through the chest wall and into the chest cavity. The surgical incision is then closed. The chest tube is placed to allow for evaluation of fluid and air from the chest cavity. This tube is typically removed two to three days after surgery. Combining the results of a number of reports on lung lobe torsion, the overall long-term survival is 50% (total of 46 patients). The sooner the patient is treated after the lung lobe torses, the better the prognosis may be.
For more information on this subject, speak to the veterinarian that is treating your pet.

For more information, here are 2 good resources:

Abstract – Lung lobe torsion in dogs: 22 cases (1981–1999)
Journal of the American Veterinary Medical Association
October 1, 2000, Vol. 217, No. 7, Pages 1041-1044

Lung Torsion