Pyothorax in Dogs
Dr. Theresa Welch Fossum
Pyothorax is a general term that denotes infection of the pleural cavity, which is the space between the lungs and the body wall. There are multiple different types of organisms that can cause pyothorax including bacteria, viruses and fungi. The infection can be associated with foreign bodies (plant materials, sticks, even toothpicks), pneumonia, tumors, abscesses in the lungs or it may be iatrogenic, which means it was caused by the veterinarian doing procedures such as chest taps or as a complication of surgery.
Bacteria may enter the chest cavity when a foreign body penetrates the rib cage or is inhaled into the lungs. In many cases, after the foreign body initiates the infection, it migrates out of the chest cavity into another site of the body or even out of the body entirely. Thus, finding the initiating culprit is often a daunting (if not impossible) task.
Extension from pneumonia may also cause an infection in the pleural cavity, although this is a less common route for the infection to occur in dogs than in people. People with pneumonia often complain of pain associated with infection of the pleura, which is the lining of the lung. With time, the pleurisy may cause fluid to develop in the chest cavity, resulting in a pyothorax.
Rarely, the esophagus may perforate (develop a leak) and infect the thoracic cavity by leaking food and bacteria. The perforation may occur when a bone or other hard tissue becomes lodged in the esophagus. With time the pressure from the object may interfere with the blood supply to the esophageal wall and eventually cause the adjacent tissue to die. When this occurs, food and fluid may spill into the chest cavity. Pyothorax of this nature is very serious and often results in death fairly quickly after the perforation occurs. Sharp objects swallowed by the animal may also perforate the esophagus and cause leakage.
Spread of infection from surrounding tissues such as the vertebrae (diskospondylitis) is a relatively rare cause of pyothorax, but it can occur. Animals with diskospondylitis often have evidence of neurologic dysfunction such as weakness, ataxia or a wobbly gate that precede the development of the pyothorax.
Tumors that grow in the lung tissue can reach such a large size that the blood supply to the tumor is no longer adequate. When this happens, a portion of the tumor may become necrotic and infected. Such a tumor may rupture and leak bacteria into the chest cavity, causing a pyothorax. Although the animal may seek a veterinarian because of breathing difficulties associated with the pyothorax, the underlying problem in these animals is actually the tumor.
Abscesses can occur in the lungs. These abscesses may be a result of a foreign body that has penetrated the lungs and is lodged there. However, the inciting foreign body frequently causes the infection and then migrates out of the lung so that it can no longer be found. Grass awns on the West Coast of the United States are notorious for causing lung abscesses in dogs, with resultant pyothorax. As pet owners know who live in areas where grass awns are common, these pieces of plant material are also frequently found under the third eyelid, in the ear canal or in the tissues of the legs or other sites of the body.
Pyothorax associated with fungal infections is relatively uncommon. Although fungal infections are frequently noted in the lungs of dogs that live in endemic areas, they are less commonly associated with chest fluid.
Whenever a needle or a chest tube is placed into the chest cavity to drain fluid or air, there is a risk that the animal will develop an infection. Thus, it is important that these procedures be done carefully and with appropriate technique to minimize this risk.
Infection of the chest cavity can be a complication of chest surgery, although this is a rare development if proper technique is used. However, to further minimize this risk, your veterinarian may ask that you give your pet antibiotics after surgery. It is important that you follow your veterinarian's instructions regarding administration of any medications before or after your pet has surgery.