An abdominal abscess is a collection of cellular debris, enzymes, and liquefied remains which can be from an infection or non-infectious source. An intra-abdominal abscess usually signals that something serious is happening to the patient. An abscess can develop almost anywhere in the abdomen but are usually confined to some part of the peritoneal cavity. In many cases, the omentum, viscera, or mesentery may wall off an intraabdominal abscess. An abdominal abscess is quite common and is a serious condition. To avoid the high morbidity and mortality, the condition must be promptly diagnosed and treated. In general, sepsis that occurs after perforation in the upper gastrointestinal (GI) tract or leak is often associated with less morbidity and mortality compared to leaks that result from a colonic perforation or injury.
The most common organisms involved in an abdominal abscess include a mixture of aerobic and anaerobic bacteria that originate from the gastrointestinal tract. Causes of an intraabdominal abscess include perforation of a gastric ulcer, perforated appendicitis, diverticulitis, ischemic bowel disease, pancreatic necrosis, or gangrenous cholecystitis. Other common causes include penetrating abdominal trauma, surgical trauma, anastomotic leaks, volvulus, intussusception, or a missed gallstone during a cholecystectomy. Less frequently sterile abscess can result from the injection of a drug.
Organisms involved in an abdominal abscess include the following:
In most cases, intra-abdominal abscesses derive from an intra-abdominal organ and often develop after operative procedures. It is estimated that about 70% are postsurgical and that 6% of patients undergoing colorectal surgery may develop a postoperative abscess. Hepatic abscesses account for 13% of all intra-abdominal abscesses. Most hepatic abscesses involve the right lobe, probably due to the larger size and greater blood supply.
An intra-abdominal abscess may be confined or generalized within the peritoneal cavity. Localized collections of pus may have a barrier that may include adhesions, omentum or other adjacent viscera. In almost all cases, abdominal abscesses contain a polymicrobial collection of both aerobic and anaerobic organisms from the GI tract. The bacteria usually incite an inflammatory reaction that often results in a hypertonic environment that continues to expand as an abscess cavity. If left untreated, an abdominal abscess can lead to septic shock.
Patients with an intra-abdominal abscess may present with abdominal pain, fever anorexia, tachycardia or prolonged ileus. The presence of a palpable mass may or may not be present. If the presentation is delayed, some individuals may appear in septic shock.
If the abscess is retroperitoneal or located deep in the pelvis, there may be no clinical signs. In such cases, the only suspicion may be a fever, mild liver dysfunction, or a prolonged ileus.
In post surgery patients, the diagnosis of an abdominal abscess is difficult because of analgesia and antibiotics which often mask the signs of an infection.
A subphrenic abscess may present with shoulder tip pain, hiccups, or atelectasis.
Most patients with an abdominal abscess will show signs of dehydration, oliguria, tachycardia, tachypnea, and respiratory alkalosis.
Blood work is not specific for an intra-abdominal abscess but may reveal leukocytosis, abnormal liver function, anemia or thrombocytopenia. These are features that signal an infection. Blood cultures are often negative but when positive may reveal predominantly anaerobic organisms, the most common being Bacteroides fragilis. Plain abdominal x-rays are not sensitive for identifying an intraabdominal abscess and hence a CT scan is required and is considered to be the most definitive test to rule out an intra-abdominal abscess. A CT scan can reveal the location, size, and presence of bowel thickening, thumbprinting, and ileus. Intra-abdominal abscess almost always requires intravenous (IV) antibiotics. If the abscess is localized, CT-guided aspiration can be performed to drain the abscess. CT scan has the advantage that it avoids general anesthesia and wound complications. It also prevents contamination of other parts of the abdominal cavity.
Broad-spectrum antibiotics and hydration are essential. Once cultures become, available one can use specific antibiotics as noted by their sensitivity. Intravenous hydration is required. A nasogastric tube may help decompress bowel and lower the emesis.
Percutaneous CT guided drainage is widely used to drain abdominal abscesses. The procedure can be done under local anesthesia and decreases the duration of hospitalization. In most patients, improve occurs within 48 hours after drainage. In localized abscesses, CT-guided drainage has a success rate of over 90%.
If the patients fail to improve within 24 to 48 hours, a surgical consultation is required. Both laparoscopic, interventional radiology and open procedures can be used to evacuate the abdominal abscess. However, if surgery is required, the necrotic tissue will be removed, and all adhesions can be lysed. Most of these patients require monitoring in the intensive care unit (ICU) and need aggressive resuscitation with fluids. If the abscess is localized and promptly treated, the prognosis is good.
Abscesses located in the pelvis may be drained transrectally or transvaginally, and the results are excellent.
Open surgery for an abdominal abscess is a difficult undertaking and can be difficult because of adhesions and lack of proper anatomical pathways to separate bowel.
The prognosis of patients with an abdominal abscess prior to the era of the CT scan was very high. Today, with the availability of CT scans the diagnosis is made much earlier, and in fact in many cases, CT guided drainage has helped lower the morbidity. However, if an abdominal abscess is misdiagnosed and not treated, the mortality is very high. Risk factors that increase the mortality and morbidity include the following:
Patients with an abdominal abscess usually require a stay in the hospital. Repeat imaging is often done to ensure that there is no more residual abscess after treatment.
Depending on the complexity of the abscess, some patients may require total parenteral nutrition.
Because the patients are often frail, physical therapy is recommended to help recover muscle strength and flexibility.
Once a diagnosis of an abdominal abscess is done, a general surgeon and a radiologist should be consulted.
Those with gross contamination of the abdominal cavity can develop multiorgan failure and consequently have a high mortality rate.
Today with the availability of CT scan, both diagnosis and drainage can be accomplished with very low morbidity.
A complex abscess may require a laparoscopic or an open approach.
An abdominal abscess is not an uncommon presentation on the general surgery ward. The disorder is best managed by a multidisciplinary group of health professional that includes a surgeon, radiologist, gastroenterologist and a wound care nurse. In many cases, the first sign of an abdominal abscess is detected by a nurse. There should not be any delay in consulting with the surgeon, as delay can lead to adverse outcomes and significant healthcare costs. Many of these patients also develop wound infections that do not heal. Hence a consult with a wound care nurse for daily dressings is necessary. Because many of these patients are not able to eat, they may require parenteral nutrition- and hence a consult with a dietitian is necessary. The progress and monitoring of patients with an abdominal abscess is made by regular physical exams, vital signs, and imaging tests. Often these patients have drainage devices that also need to be monitored for the type and amount of fluid discharge. The pharmacist should follow up with the culture results and ensure that the patient is on the appropriate antibiotics. Only through a systematic approach can the morbidity and mortality of an abdominal abscess be lowered. (Level III)
The outcomes after an abdominal abscess depend on patient morbidity, the cause, extent of contamination and age. When multiple organs are involved and the patient is septic, the outcomes are poor. However, for localized abscesses from a rupture of an appendix or sigmoid diverticulitis, the outcomes are good. Many of these patients have significant comorbidity which affects their long-term survival. The key to improving the mortality is prompt diagnosis and early treatment.  (Level V)