A subdiaphragmatic abscess is an infectious process characterized as a collection of purulent fluid between the diaphragm and the liver or spleen. Most typically, these abscesses form following surgery, but they can also result from intraperitoneal spread in the setting of intraabdominal infections (eg, ruptured appendix, perforated peptic ulcer disease, complicated diverticulitis, liver abscesses, or cholecystitis with perforation).

This space is separated into 4 intraperitoneal and 2 extraperitoneal spaces. The falciform ligament divides the space into right and left, and each side is further divided into anterior and posterior spaces by the lateral ligaments. The left extraperitoneal space is just above the pole of the kidney, and the right extraperitoneal space is between the layers of the coronary ligaments.

Patients present with fever, abdominal pain, cough, and dyspnea. If diagnosis and treatment is expedited, many patients will achieve full recovery. If left untreated or if severe sepsis or respiratory failure develops, subdiaphragmatic abscesses can be potentially fatal.