Intraabdominal abscesses and fistulas occur due to a septic process within the abdominal cavity and are often interconnected. Various inflammatory and infective disease processes can lead to these conditions. They may also be iatrogenic, occurring as complications of procedures and operations within the abdominal cavity. They can cause significant effects on health and quality of life. Accurate diagnosis requires clinical acumen and appropriate imaging while management needs multidisciplinary expertise.

Intraabdominal abscesses are contained areas of infection, which present as pockets of pus within the abdominal cavity. They occur most commonly in certain dependent spaces within the peritoneum, such as in the subphrenic space, the paracolic gutters, or within the pelvis (Figure 63.1). Intraabdominal abscesses form when infection occurs due to bacterial contamination of the peritoneal cavity. The immune response then attempts to eliminate and contain the infection. Abscesses can occur in the postoperative setting (Figures 63.2 and 63.3). Other causes include penetrating trauma, spontaneous perforation of a hollow viscus, primary or metastatic infection, inflammation such as Crohn’s disease, and ischemia. Diseases of the gastrointestinal tract such as appendicitis and diverticulitis (Figures 63.4 and 63.5), the genitourinary tract (see Figure 63.3), or the hepatobiliary system and pancreas can lead to abscess formation within the abdomen.

Gastrointestinal fistulas commonly occur in association with abscesses. They are defined as abnormal communications between the gastrointestinal tract and another epithelialized surface. Fistulas can be classified by anatomical location, physiological characteristics (that is, fluid output), or by etiology. The vast majority of gastrointestinal fistulas are acquired as a result of previous abdominal surgery. Alternatively, spontaneous fistulas can occur in the setting of inflammatory disorders, such as Crohn’s disease (Figure 63.6), or in relation to radiation, necrosis or malignancy (Figure 63.7).

Advances in imaging technology have revolutionized the diagnosis and assessment of intraabdominal abscesses and fistulas. Contrast‐enhanced computed tomography (CT) accurately detects abscess cavities and allows percutaneous drainage (Figure 63.8; see also Figures 63.3 and 63.4). Magnetic resonance imaging (MRI) (Figures 63.9 and 63.10) and ultrasound (Figure 63.11) have the advantage of avoiding exposure to ionizing radiation. MRI is of particular use in patients with fistulas and when anatomical detail is needed. In specific circumstances, contrast radiography still has a role to play (Figure 63.12).