Intra-abdominal, Visceral, and Retroperitoneal Abscesses

Etiology

Complicated appendicitis is the most common cause of intra-abdominal abscesses in children. Patients can develop an abscess after perforation of the appendix, or the abscess can develop after an appendectomy. Intra-abdominal abscesses also can originate from the gastrointestinal tract, especially in patients with inflammatory bowel disease or in those who are immunocompromised. Any surgical procedure involving the gastrointestinal tract can result in a postoperative abscess. These abscesses can result either from contamination of the peritoneum at the time of surgery or as a result of a postoperative anastomotic leak. A perforated viscus associated with necrotizing enterocolitis, peptic ulcer, Meckel diverticulum, and trauma also can result in intra-abdominal abscesses. The location of an abscess within the abdominal cavity may suggest an underlying condition or certain pathogens. For example, intra-abdominal abscesses near the terminal ileum suggest the possibility of inflammatory bowel disease. The bacteria most frequently isolated in abscesses after bowel disease or surgery include Escherichia coli, Bacteroides species, and Enterococcus species, but any enteric organism can be present. In one study evaluating the microbiology of intra-abdominal abscesses in children, 8% of cultures yielded only facultative bacteria, 17% only anaerobic bacteria, and 75% mixed flora. ^,

Although uncommon, the incidence of biliary tract disease among children is increasing. Children with hemolytic disorders such as sickle cell disease and hereditary spherocytosis are at increased risk for cholelithiasis and biliary tract disease. Although most cases of cholelithiasis in children are managed electively, some patients have complicated disease and associated cholecystitis. These patients are at risk for postoperative abscess formation, which should be suspected if there is persistent fever and right upper quadrant pain after cholecystectomy. If there is a bile duct injury, a bile leak can occur postoperatively; the resulting collection of bile can become infected and require drainage. A retained gallstone in the peritoneal cavity after cholecystectomy can be another source of intra-abdominal abscess.

Clinical Manifestations

In addition to fever, symptoms may result from compression of the abscess on adjacent structures, such as early satiety for abscesses near the stomach, urinary frequency or urgency for those near the bladder, or diarrhea or tenesmus for abscesses near the colon or rectum. Anorexia and weight loss also may be present. In patients who have undergone cholecystectomy, persistent fever and right upper quadrant pain should prompt suspicion for postoperative abscess.

Diagnosis

When an intra-abdominal abscess is suspected, imaging is indicated. Early post-operative imaging may be difficult to interpret because of post-surgical fluid collections, which may lead to unnecessary interventions. Persistence of fever and abdominal pain for 5–7 days after abdominal surgery should prompt evaluation for an abscess. ^, Although plain radiographs of the abdomen can show indirect evidence of abscess such as a pleural or peritoneal effusion or ileus, the diagnosis is confirmed by more advanced imaging. Ultrasonography (US) can identify the location and size of an abscess in most cases and avoids exposure to ionizing radiation. CT, with contrast if possible, should be used when the US is nondiagnostic ( Fig. 66.1 ). These studies also provide guidance for aspiration and placement of drainage catheters.

MRI, although more costly, is emerging as a favored imaging modality for appendicitis due to its comparable sensitivity and specificity to CT without exposure to contrast and radiation. Some centers have adopted quick non-contrast MRI protocols using limited, fluid-sensitive sequences to evaluate post-appendicitis abscess with promising results. ^, In one study comparing 16 patients with suspected post-appendicitis abscess who underwent quick MRI with 16 historical controls who underwent CT scan for the same indication, there were no significant differences in ability to diagnose abscess, type of drainage procedure, or outcomes, including length of hospitalization or readmission.