An abdominal abscess is a localized collection of pus that accumulates inside the abdominal cavity or adjacent to an internal organ. Pus is a mixture of dead white blood cells, bacteria, and tissue debris. The immune system forms a defensive barrier of inflamed tissue around this infected fluid pocket to prevent the infection from spreading. Because the abdomen houses many vital organs, an infection trapped here requires prompt medical attention. If left untreated, the bacteria can multiply and potentially lead to a life-threatening systemic response, such as sepsis.
Defining an Abdominal Abscess and Its Causes
An abscess forms when bacteria enter a sterile area, triggering an immune response that results in the accumulation of pus. This infection can be categorized based on its location. An intra-abdominal abscess is located within the peritoneal space among the organs, while a retroperitoneal abscess forms behind the lining of the abdominal cavity. The body walls off the infection, creating a cavity that can range from a small fluid collection to a large mass.
The most common cause for an abdominal abscess is a complication following recent abdominal surgery, where intestinal bacteria may contaminate the area. Other primary causes involve the perforation or rupture of an organ, such as a burst appendix or a hole in the colon due to diverticulitis. Inflammatory conditions like Crohn’s disease or other forms of inflammatory bowel disease (IBD) can also increase the risk by causing fistulas or leaks in the intestinal wall. Additionally, trauma to the abdomen can introduce bacteria and lead to the development of an infected fluid collection.
Recognizing the Warning Signs
The symptoms experienced often mirror those of a generalized infection and serve as the first indication that an abdominal abscess has formed. Persistent abdominal pain is a common sign, which can be localized to the specific area of the abscess and intensifies with movement or deep breaths. For instance, an abscess beneath the diaphragm might cause referred pain in the shoulder, while a pelvic abscess causes lower abdominal discomfort.
The presence of a systemic infection is signaled by a high fever and chills, often exceeding 100.4°F (38°C). Patients report a general feeling of being unwell (malaise), along with loss of appetite and unexplained weight loss. Digestive distress is frequent, manifesting as nausea, vomiting, or changes in bowel habits, such as diarrhea or constipation. Any combination of these symptoms, especially following a recent surgery or a known inflammatory condition, requires immediate consultation.
Diagnosis and Treatment Pathways
Confirming the presence of an abdominal abscess involves a combination of laboratory and imaging tests to visualize the infected fluid collection. Initial blood work shows an elevated white blood cell count (leukocytosis), which indicates a significant infection within the body. Inflammatory markers like C-reactive protein (CRP) may also be high.
The definitive diagnostic tool is a contrast-enhanced computed tomography (CT) scan of the abdomen. This scan is the standard for accurately locating the abscess, determining its size, and identifying its relationship to surrounding organs. Ultrasound may also be utilized, particularly for fluid pockets near the liver or pelvis. Once the abscess is localized, treatment must begin quickly, as antibiotics alone are insufficient because the pus pocket impedes their full penetration.
The standard treatment involves a two-pronged approach: the administration of appropriate antibiotics and the physical removal of the pus through a drainage procedure. Broad-spectrum antibiotics are started immediately to control the systemic infection until laboratory cultures from the drained pus can guide a more targeted therapy. The preferred method for removing the infected fluid is percutaneous drainage, a minimally invasive technique performed by an interventional radiologist.
During percutaneous drainage, imaging guidance (usually CT or ultrasound) is used to insert a thin needle through the skin and into the abscess cavity. A drainage catheter, a small flexible tube, is then left in place to allow the pus to continuously drain over several days to weeks. This technique is successful in a high percentage of cases and is favored because it avoids the need for open surgery. Surgery may still be required if the abscess is complex, contains thick debris, or is in a location that cannot be safely reached with a needle.