Pus in the Chest Cavity of Cats

4 min read

Pyothorax in Cats

Pyothorax occurs when pus, the body's natural immune response to an invasion of bacteria, accumulates in the chest (pleural) cavity. Made up of white blood cells (neutrophils) and dead cells, pus gathers at the site of an infection. Eventually, the white blood cells die, leaving the thick whitish-yellow fluid that is characteristic of pus.

Pus that accumulates in the chest cavity, however, differs from an abscess, in that it does not create an enclosed wall of tissue to inhibit the bacteria from spreading. Instead, the pus forms into sacs that line the pleura, eventually scarring the cavity and severely impairing lung function.

A bacterial infection that settles in the cat's chest cavity can enter from the lungs or esophagus. Cats generally get these types of infections from bite wounds, but they can also get them from inhaling foreign bodies, or from the spread of a lung infection, such as pneumonia, into the chest cavity.

The condition described in this medical article can affect both dogs and cats. If you would like to learn how pyrothorax affects dogs, please visit this page in the PetMD health library.

Symptoms and Types

Cats with pyothorax commonly display such symptoms as shock and sudden respiratory distress; they may also collapse.


The most common causes for pyrothorax include infections with the bacteria:

  • Pasteurella Multocida
  • Bacteroides
  • Peptostreptococcus
  • Fusobacterium

Other causes include:

  • Cancer
  • Parasitic infestation (e.g., Spirocerca lupi)
  • Lung torsion (twisting of a lung lobe)
  • The presence of foreign objects within the chest cavity
  • Rupture of inflamed, granulated tumor in the esophagus


You will need to give a thorough history of your cat's health to the veterinarian, as well as its symptoms and possible incidents that might have preceded this condition, such as any fight wounds or chest injuries your pet might have sustained.

Your veterinarian will perform a thorough physical exam, checking your cat’s chest for inflammation of cellular tissue (cellulites) or scarring. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, electrolyte panel. In addition, a urinalysis sample of fluid from the chest cavity will be sent to the laboratory for cytologic (microscopic) evaluation and gram staining -- a procedure that makes bacteria more visible by causing it to stand out from the other cells.

A sample of the fluid in the pleural cavity will be sent for aerobic and anaerobic bacterial cultures (bacteria that need oxygen, and bacteria that does not, respectively), and for serological testing to detect the presence of a fungal agent. If the parasite S. lupi is suspected, an examination of the esophagus (esophagoscopy) can be done.

Your veterinarian can also use X-ray and ultrasound imaging to examine the interior of the cat's chest cavity. These images will show fluid in the chest cavity, possible lung hardening (consolidation), lung collapse, and/or masses.

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