(See also Acute Abdominal Pain Acute Abdominal Pain Abdominal pain is common and often inconsequential. Acute and severe abdominal pain, however, is almost always a symptom of intra-abdominal disease. It may be the sole indicator of the need... read more .)
Etiology of Intra-Abdominal Abscesses
Intra-abdominal abscesses are classified as intraperitoneal, retroperitoneal, or visceral (see table Intra-Abdominal Abscesses Intra-Abdominal Abscesses Abscesses can occur anywhere in the abdomen and retroperitoneum. They mainly occur after surgery, trauma, or conditions involving abdominal infection and inflammation, particularly when peritonitis... read more 
). Many intra-abdominal abscesses develop after perforation of a hollow viscus or colonic cancer. Others develop by extension of infection or inflammation resulting from conditions such as appendicitis Appendicitis Appendicitis is acute inflammation of the vermiform appendix, typically resulting in abdominal pain, anorexia, and abdominal tenderness. Diagnosis is clinical, often supplemented by CT or ultrasonography... read more 
, diverticulitis Colonic Diverticulitis Diverticulitis is inflammation with or without infection of a diverticulum, which can result in phlegmon of the bowel wall, peritonitis, perforation, fistula, or abscess. The primary symptom... read more 
, Crohn disease Crohn Disease Crohn disease is a chronic transmural inflammatory bowel disease that usually affects the distal ileum and colon but may occur in any part of the gastrointestinal tract. Symptoms include diarrhea... read more 
, pancreatitis Overview of Pancreatitis Pancreatitis is classified as either acute or chronic. Acute pancreatitis is inflammation that resolves both clinically and histologically. Chronic pancreatitis is characterized by histologic... read more , pelvic inflammatory disease Pelvic Inflammatory Disease (PID) Pelvic inflammatory disease (PID) is a polymicrobial infection of the upper female genital tract: the cervix, uterus, fallopian tubes, and ovaries; abscess may occur. PID may be sexually transmitted... read more , or indeed any condition causing generalized peritonitis Peritonitis Abdominal pain is common and often inconsequential. Acute and severe abdominal pain, however, is almost always a symptom of intra-abdominal disease. It may be the sole indicator of the need... read more . Abdominal surgery, particularly that involving the digestive or biliary tract, is another significant risk factor: The peritoneum may be contaminated during or after surgery from such events as anastomotic leaks. Traumatic abdominal injuries—particularly lacerations and hematomas of the liver, pancreas, spleen, and intestines—may develop abscesses, whether treated operatively or not.
The infecting organisms typically reflect normal bowel flora and are a complex mixture of anaerobic and aerobic bacteria. Most frequent isolates are
Aerobic gram-negative bacilli (eg, Escherichia coli Escherichia coli Infections The gram-negative bacterium Escherichia coli is the most numerous aerobic commensal inhabitant of the large intestine. Certain strains cause diarrhea, and all can cause infection when they invade... read more and Klebsiella Klebsiella, Enterobacter, and Serratia Infections The gram-negative bacteria Klebsiella, Enterobacter, and Serratia are closely related normal intestinal flora that rarely cause disease in normal hosts. Diagnosis is by culture. Treatment is... read more )
Intra-Abdominal Abscesses
Symptoms and Signs of Intra-Abdominal Abscesses
Abscesses may form within 1 week of perforation or significant peritonitis, whereas postoperative abscesses may not occur until 2 to 3 weeks after operation and, rarely, not for several months. Although manifestations vary, most abscesses cause fever and abdominal discomfort ranging from minimal to severe (usually near the abscess). Paralytic ileus, either generalized or localized, may develop. Nausea, anorexia, and weight loss are common.
Abscesses in the Douglas cul-de-sac, adjacent to the rectosigmoid junction, may cause diarrhea. Contiguity to the bladder may result in urinary urgency and frequency and, if caused by diverticulitis, may create a colovesical fistula.
Subphrenic abscesses may cause chest symptoms such as nonproductive cough, chest pain, dyspnea, hiccups, and shoulder pain. Rales, rhonchi, or a friction rub may be audible. Dullness to percussion and decreased breath sounds are typical when basilar atelectasis, pneumonia, or pleural effusion occurs.
Generally, there is tenderness over the location of the abscess. Large abscesses may be palpable as a mass.
Complications
Undrained abscesses may extend to contiguous structures, erode into adjacent vessels (causing hemorrhage or thrombosis), rupture into the peritoneum or bowel, or form a cutaneous or genitourinary fistula. Subdiaphragmatic abscesses may extend into the thoracic cavity, causing an empyema, lung abscess Lung Abscess Lung abscess is a necrotizing lung infection characterized by a pus-filled cavitary lesion. It is most commonly caused by aspiration of oral secretions by patients who have impaired consciousness... read more 
, or pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more . An abscess in the lower abdomen may track down into the thigh or perirectal fossa. Splenic abscess is a rare cause of sustained bacteremia in endocarditis that persists despite appropriate antimicrobial therapy.
Diagnosis of Intra-Abdominal Abscesses
Abdominal CT
Rarely radionuclide scanning
CT of the abdomen and pelvis with oral contrast is the preferred diagnostic modality for suspected abscess. Other imaging studies, if done, may show abnormalities; plain abdominal x-rays may reveal extraintestinal gas in the abscess, displacement of adjacent organs, a soft-tissue density representing the abscess, or loss of the psoas muscle shadow. Abscesses near the diaphragm may result in chest x-ray abnormalities such as ipsilateral pleural effusion, elevated or immobile hemidiaphragm, lower lobe infiltrates, and atelectasis.
A complete blood count and blood cultures should be done. Leukocytosis occurs in most patients, and anemia is common.
Occasionally, radionuclide scanning with indium-111–labeled leukocytes may be helpful in identifying intra-abdominal abscesses.
Prognosis for Intra-Abdominal Abscesses
Intra-abdominal abscesses have a mortality rate of 10 to 40%. Outcome depends mainly on the patient’s primary illness or injury and general medical condition rather than on the specific nature and location of the abscess.
Treatment of Intra-Abdominal Abscesses
IV antibiotics
Drainage: Percutaneous or surgical
Almost all intra-abdominal abscesses require drainage, either by percutaneous catheters or surgery; exceptions include small (< 2 cm) pericolic or periappendiceal abscesses, or abscesses that are draining spontaneously to the skin or into the bowel. Drainage through catheters (placed with CT or ultrasound guidance) may be appropriate given the following conditions:
Few abscess cavities are present.
The drainage route does not traverse bowel or uncontaminated organs, pleura, or peritoneum.
The source of contamination is controlled.
The pus is thin enough to pass through the catheter.
Antibiotics are not curative but may limit hematogenous spread and should be given before and after intervention. Therapy requires IV drugs active against bowel flora. Patients with community-acquired infection should be characterized as at low or high risk of treatment failure or death based on signs of sepsis or septic shock Symptoms and Signs Sepsis is a clinical syndrome of life-threatening organ dysfunction caused by a dysregulated response to infection. In septic shock, there is critical reduction in tissue perfusion; acute failure... read more , extremes of age, comorbidities, extent of abdominal infection, and risk of resistant bacteria. For community-acquired infection in patients at low risk, recommended regimens include ertapenem as a single drug or metronidazole plus either cefotaxime or ceftriaxone. For community-acquired infection in patients at high risk, recommended regimens include piperacillin/tazobactam, cefepime plus metronidazole, imipenem/cilastatin, or meropenem. Patients previously given antibiotics or those who have hospital-acquired infections should receive drugs active against resistant aerobic gram-negative bacilli (eg, Pseudomonas) and anaerobes. (See also the Surgical Infection Society's 2017 revised guidelines on the management of intra-abdominal infection.)
Nutritional support is important, with the enteral route preferred. Parenteral nutrition should begin early if the enteral route is not feasible.
Key Points
Suspect abdominal abscess in patients with a previous causative event (eg, abdominal trauma, abdominal surgery) or condition (eg, Crohn disease, diverticulitis, pancreatitis) who develop abdominal pain and fever.
Abscess may be the first manifestation of a cancer.
Diagnosis is with abdominal CT.
Treatment is percutaneous or surgical drainage; antibiotics are necessary but alone are not adequate treatment.
More Information
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
Surgical Infection Society: Revised Guidelines on the Management of Intra-Abdominal Infection (2017)
