A peritoneal abscess is a severe infection localized within the abdominal cavity. An abscess is a walled-off pocket filled with pus, a thick fluid composed of dead white blood cells, bacteria, and tissue debris. In the abdomen, this collection forms within the space surrounding the digestive organs, known as the peritoneal cavity. This serious condition requires prompt medical intervention to prevent widespread complications.
Defining the Condition and Its Location
The peritoneum is a continuous, thin membrane that lines the interior of the abdominal wall and covers the organs within the abdomen. It consists of two layers: the parietal peritoneum (on the wall) and the visceral peritoneum (covering the organs), separated by the peritoneal cavity. A peritoneal abscess forms when infectious material collects and becomes encapsulated by surrounding tissues within this cavity. This containment prevents the infection from spreading throughout the abdominal space.
The abdominal cavity’s geography creates specific recesses where infection tends to accumulate. Common sites include the subphrenic spaces (beneath the diaphragm) and the subhepatic space (under the liver). The paracolic gutters, channels running along the sides of the colon, can funnel infected fluid into the deep recesses of the pelvis, making pelvic abscesses frequent. The location of the abscess often provides a clue to the original source of the infection.
How Peritoneal Abscesses Form
Peritoneal abscesses almost always arise from bacterial contamination of the sterile peritoneal cavity, typically originating from the gastrointestinal tract. This contamination usually occurs when a hollow organ ruptures or leaks its contents. Examples include a burst appendix, a perforated peptic ulcer, or a tear caused by severe diverticulitis. Bacteria, such as Escherichia coli and Bacteroides fragilis, spill into the abdominal space, triggering a massive inflammatory response when they enter the peritoneum.
The body attempts to localize this influx of bacteria by creating a fibrous wall around the infection. This walling-off process involves the omentum and nearby organs adhering to the site, resulting in the encapsulated pus collection. Abdominal surgery is a significant risk factor, particularly due to anastomotic leaks (leaks from a surgical connection) or contamination during the procedure. Underlying conditions like inflammatory bowel disease or trauma to an abdominal organ can also predispose an individual to developing these localized infections.
Symptoms, Diagnosis, and Treatment
The signs of a peritoneal abscess vary depending on location but typically reflect a deep-seated infection. Most patients experience a fever and constant abdominal pain ranging from mild to severe. Abscesses under the diaphragm may cause referred pain in the chest or shoulder. A pelvic abscess might lead to rectal tenderness or changes in bowel habits. Other common symptoms include loss of appetite and nausea.
Diagnosis begins with a physical examination and blood tests, which often reveal a high white blood cell count. The most definitive diagnostic tool is imaging, with a computed tomography (CT) scan being the preferred method. The CT scan clearly visualizes the abdomen, precisely locating the pocket of pus, measuring its size, and determining its relationship to surrounding organs. Ultrasound is another non-invasive imaging technique often used to guide subsequent treatment procedures.
Treatment relies on two main strategies: eliminating the infectious source and providing appropriate medication. Source control is the most important step and involves physically removing the pus from the encapsulated space. This is often achieved through percutaneous drainage, where an interventional radiologist uses imaging guidance (such as a CT scan) to insert a needle and a small catheter through the skin into the abscess. The catheter remains in place to drain the infected fluid into an external bag, allowing the cavity to collapse and heal.
For abscesses difficult to reach or highly complex, surgical drainage may be necessary to fully clean out the infected area. Alongside drainage, powerful antibiotics are administered intravenously to combat the bacterial infection, targeting the mixture of aerobic and anaerobic organisms. Antibiotic therapy alone is insufficient because the thick, walled-off pus collection prevents the medication from reaching therapeutic concentrations inside the abscess. The combination of drainage and targeted antibiotics is necessary for successful resolution and prevents life-threatening complications like widespread sepsis.