Pyothorax

Pyothorax refers to the accumulation of infected fluid—pus—in the pleural space, the thin gap between the lungs and the chest wall. This space is normally empty except for a small amount of lubricating fluid; when infection takes hold, the space can fill with material that prevents the lungs from expanding properly. The condition can develop after a penetrating wound, from the spread of infection elsewhere in the chest, or sometimes without an obvious external cause. Owners often notice difficulty breathing, reduced appetite, lethargy, or a generally unwell appearance that may come on over days or occasionally more suddenly. Cats are affected more commonly than dogs, though the condition can occur in either species. The signs can resemble other causes of breathing difficulty, and the presentation varies depending on how much fluid has accumulated and how quickly it has developed. This page explores the signals that may point towards pyothorax, the mechanisms by which infection becomes established in the chest, the investigations used to identify it and guide decisions, and the range of approaches used to manage the condition.