Intraabdominal abscesses

Intrabdominal abscesses (IAAs) are a relatively common manifestation of intrabdominal infections and can occur in almost any structure or compartment of the abdomen. Sources include infected intraabdominal organs, organ or viscus perforation, surgical site infections, and the spread of extraabdominal infections. Most IAAs present with nonspecific abdominal pain, fever, and/or sepsis. Large abscesses may be palpable on examination, but imaging with abdominal ultrasound or CT abdomen is typically required for the diagnosis. Treatment includes sepsis management, antibiotics, rapid source control with abscess drainage, and treatment of the underlying disorder. IAAs > 3 cm in diameter generally require drainage. Imaging-guided percutaneous drainage is usually preferred, but surgical drainage may be necessary in some cases. The choice of antibiotic treatment depends on location and source of the abscess as well as other factors such as local resistance patterns. Management of the underlying disorder is often affected by the presence and extent of related abscesses and should be adjusted accordingly.

• Infection or inflammation of intraabdominal organs, e.g., appendicitis, diverticulitis, cholecystitis, pelvic inflammatory disease
• Extrusion of intrabdominal flora, e.g., gastrointestinal perforation, bile leak
• Surgical site infections after e.g., open or laparoscopic surgery, insertion of indwelling devices, endoscopy
• Hematogenous spread of extra-abdominal infections, e.g., infective endocarditis, CLABSI

• Abdominal pain
• Fever
• Clinical features of sepsis
• Gastrointestinal symptoms, e.g., nausea and vomiting, ileus, diarrhea
• Palpable mass may be present

General principles

• IAAs are most often diagnosed on imaging when investigating:
  • Abdominal pain with fever and/or sepsis
  • Conditions that can be complicated by abscess formation, e.g., appendicitis, pyelonephritis, inflammatory bowel disease
• The optimal initial modality depends on the suspected location of the fluid collection, underlying disorder, and need for operative planning.
• Laboratory studies can assist but are not required to make the diagnosis (see “Diagnostic workup of acute abdomen” and “Septic workup”).

Imaging ^[3][4]

• CT abdomen pelvis with IV contrast ^[1]
  • Preferred initial imaging in most cases due to higher accuracy and detail of IAA characteristics
  • Most often the diagnostic modality of choice for the suspected underlying condition
  • Often required for planning drainage (See “Management.”)
  • Findings include:
    • Fluid collections with contrast enhancement
    • Signs of the underlying cause (e.g., bowel wall thickening in diverticulitis)
• US abdomen
  • Appropriate initial study for:
    • Children and pregnant individuals
    • Patients with IAAs of suspected biliary or gynecological origin
  • Lower sensitivity, especially for deep or small fluid collections
  • Findings include:
    • Hypoechoic fluid collections without signs of vascularization (e.g., Doppler flow)
    • Signs of the underlying cause (e.g., target sign in appendicitis)
• MRI abdomen
  • Reasonable initial imaging in patients for whom radiation must be minimized and US is inconclusive ^[2]
  • High sensitivity; but availability and turnaround time may be limited.
  • Findings: similar to CT

See “Acute abdominal pain” and “Fever.”

The differential diagnoses listed here are not exhaustive.

Antibiotics ^[2][5][6]

• Begin broad-spectrum empiric antibiotics for intraabdominal infection.
• Narrow coverage based on:
  • The source identified on imaging
  • Local flora and resistance patterns
  • Culture and sensitivity results
  • Local protocols
• The duration of antibiotics depends on the underlying condition, location, and drainage of the abscess.

If patients present with signs of sepsis, begin stabilization and sepsis management immediately.

Drainage ^[1][2][5][6]

• Drainage is typically indicated for most abscesses > 3 cm in diameter.
• Conservative management may be appropriate for select abscesses , but is associated with high rates of treatment failure ^[7]
• Decisions about the optimal method are multifactorial and typically made in consultation with a surgeon and interventional radiologist.

Imaging-guided percutaneous drainage ^[7]

• Preferred initial drainage method for most intraabdominal abscesses and infected fluid collections
• Performed by interventional radiology
• Usually CT-guided, but can be ultrasound-guided in some cases ^[8]
• Contraindications include:
  • Peritonitis
  • Active bleeding
  • Poorly defined abscess wall
  • Access impeded by surrounding anatomy
  • Uncorrected coagulopathy or thrombocytopenia

In patients with INR > 1.5 or platelet count < 50,000/mm³, correct coagulopathy with anticoagulation reversal or platelet transfusion before attempting imaging-guided percutaneous drainage. ^[9][10][11]

Open or laparoscopic surgical drainage ^[1][2]

• Performed by a qualified surgeon
• Typically reserved for patients with:
  • Abscesses not amenable to percutaneous drainage (e.g., inaccessible, multiloculated)
  • Unsuccessful percutaneous drainage
  • Underlying condition requiring surgical treatment (e.g., gallbladder perforation)
  • Peritonitis
  • Intraperitoneal free air

Endoscopic drainage ^[12][13]

• Performed by gastroenterology or general surgery
• Can be an option for deeper collections easily accessible through the bowel or biliary tract

• Definition: an accumulation of pus located directly under the diaphragm
• Epidemiology
  • Reported in ∼ 2% of patients post abdominal surgery
  • No history of surgery in approx. 10% of patients
• Etiology: polymicrobial infection (e.g., due to Enterococcus spp., E. coli, and Clostridium spp.) following intraperitoneal perforation
  • Most commonly a complication of surgery (e.g., splenectomy, gastrectomy) or secondary to conditions such as diverticulitis, duodenal ulcers, and appendicitis
  • Trauma
• Pathophysiology: See “Abscess” for details.
• Clinical features: most commonly develop 3–6 weeks after inciting event
  • Fever
  • Pain over the 8^th–11^th ribs on the affected side
  • Cough, increased respiratory rate, pleural effusion
• Diagnostics ^[15]
  • CBC: leukocytosis
  • Ultrasound can be used to visualize the abscess.
  • Chest x-ray shows air below the diaphragm.
• Management: abscess drainage and antibiotic treatment (empiric, followed by tailored treatment according to antibiogram)
• Complications: empyema, sepsis
• Prognosis: high mortality (∼ 30%)

• Definition: an accumulation of pus located below the liver
• Etiology
  • Cholecystitis
  • Complication of cholecystectomy
  • Perforated duodenal or gastric ulcer
• Clinical features
  • Fever
  • Vomiting
  • Diffuse abdominal pain
  • Abdominal rigidity
• Diagnostics: well-demarcated, subhepatic, nonhomogeneous fluid density which may contain gas
• Management
  • Abscess drainage and antibiotic treatment
  • Treatment of the underlying cause
  • See also “Treatment” in “Pyogenic liver abscess.”

• Definition: an enclosed collection of pus within the spleen that is usually caused by hematogenous spread of bacteria from a septic source
• Epidemiology
  • Uncommon in the general population ^[18]
  • Frequent in individuals with bacterial endocarditis (up to 30%)
  • Associated with immunocompromise in up to 35% of cases (e.g., due to HIV/AIDS, organ transplantation, malignancy) ^[17]
• Pathophysiology
  • Most common: predisposing factors such as immunodeficiency, intravenous drug use, trauma to the spleen, diabetes, and infectious conditions (especially endocarditis) → bacteremia and hematogenous spread → splenic abscess
  • Infection of splenic infarction can also lead to a splenic abscess.
• Clinical features
  • Fever
  • Left upper quadrant pain, referred left shoulder pain (Kehr sign)
• Diagnostics
  • Blood count: leukocytosis
  • Chest x-ray: left upper quadrant mass, extraluminal air, pleural effusion, and elevated diaphragm on the left side
  • CT: lesion with hypodense center and thick, heterogeneous rim
• Management
  • Broad-spectrum empirical antibiotic treatment followed by tailored treatment after blood culture results are obtained
  • Gold standard: splenectomy
  • Alternative: CT/ultrasound-guided percutaneous drainage or surgical drainage

• See “Pyogenic liver abscess.”
• See “Amebic liver abscess.”

• See “Periappendiceal abscess.”
• See “Complicated diverticulitis.”
• See “Crohn disease” and “Ulcerative colitis.”
• See “Gastrointestinal perforation.”
• See “Surgical site infection” and “Complications of abdominal surgery.”
• See “Pancreatic abscess.”
• See “Psoas abscess.”

• See “Perinephric abscess.”
• See “Tuboovarian abscess.”