What is the best course of treatment for an adult patient with a recent history of trauma or surgery, presenting with an intraperitoneal abscess formation in the left upper abdomen, accompanied by perilesional fat stranding, lymphadenopathy, gastric and bowel thickening?

Management of Intraperitoneal Abscess in the Left Upper Abdomen

This patient requires immediate CT imaging to confirm the diagnosis, followed by combined broad-spectrum intravenous antibiotics and percutaneous drainage as first-line therapy, with surgical intervention reserved for drainage failure or clinical deterioration. 1

Immediate Diagnostic Approach

• CT scan is mandatory for patients not undergoing immediate laparotomy to determine the presence, location, and characteristics of the intra-abdominal infection 1
• CT will identify the abscess size, presence of free air, bowel wall thickening, perilesional fat stranding, and help differentiate simple from complex collections 1
• Blood cultures are not routinely necessary for community-acquired infections unless the patient appears clinically toxic or is immunocompromised 1

Resuscitation and Initial Stabilization

• Begin rapid intravascular volume restoration immediately when intra-abdominal infection is suspected, even before imaging confirmation 1
• For patients with septic shock, resuscitation must start immediately upon recognition of hypotension 1
• Monitor for signs of organ dysfunction and physiologic instability requiring ICU-level care 1

Antimicrobial Therapy

• Start broad-spectrum antibiotics immediately once intra-abdominal infection is diagnosed or strongly suspected 1
• For patients with septic shock, administer antibiotics as soon as possible; for stable patients, initiate therapy in the emergency department 1
• Empiric coverage must include both aerobic gram-negative bacilli and anaerobes 1, 2
• Piperacillin-tazobactam 3.375g IV every 6 hours (or 4.5g every 6 hours for severe infections) is FDA-approved for intra-abdominal infections including peritonitis and abscess 2
• Alternative: Meropenem for severe infections or when resistant organisms are suspected 3
• Maintain adequate drug levels during any source control procedure, which may require additional dosing immediately before intervention 1

Source Control Strategy

For Abscesses 3-6 cm or Larger:

• Percutaneous CT or ultrasound-guided drainage is the preferred initial approach over surgical drainage when feasible 1
• This minimizes procedural morbidity with 80% success rates when strict criteria are met 1, 4, 5
• Place a sump drain (such as Von Sonnenberg type) for optimal drainage 5
• Success rates: 65% after first drainage, 85% after second attempt if needed 5

For Abscesses <3-4 cm:

• Antibiotics alone may be attempted in hemodynamically stable patients with small, well-localized collections 1
• This requires very close clinical monitoring with low threshold for escalation to drainage or surgery 1
• Failure rates with antibiotics alone for abscesses 4-6 cm range from 18-44% 1

Indications for Immediate Surgical Intervention:

• Diffuse peritonitis with hemodynamic instability requires emergency surgery as soon as possible 1
• Failure of percutaneous drainage (persistent fever, increasing abscess size, clinical deterioration) 1
• Complex abscesses with multiple loculations, fecal fistula, or bowel discontinuity 4, 6
• Presence of distant free intraperitoneal air with diffuse fluid (suggests perforation with ongoing contamination) 1
• Inability to achieve adequate percutaneous access 1

Special Considerations for Left Upper Quadrant Location

Given the anatomic location with gastric and bowel wall thickening:

• Consider underlying gastric or splenic pathology as the source (perforated ulcer, splenic abscess, diverticulitis if involving splenic flexure) 1
• Gastric perforation may present with minimal peritonitis initially but requires urgent intervention 1
• If splenic abscess is identified, surgical splenectomy is often necessary as percutaneous drainage has limited success 6
• The transgluteal or posterior approach may be needed for drainage if anterior access is limited 5

Monitoring and Follow-up

• Reassess clinically within 24-48 hours after initiating treatment 1
• Repeat imaging if no clinical improvement within 48-72 hours 1
• Continue antibiotics until resolution of physiological abnormalities (fever, leukocytosis, tachycardia) 1
• Typical antibiotic duration is 7-10 days for adequately drained abscesses 1, 2
• Remove drainage catheter when output is minimal (<10-20 mL/day) and patient is clinically improved, typically after 5-6 days 5, 7

Critical Pitfalls to Avoid

• Do not delay source control beyond 24 hours in stable patients receiving appropriate antibiotics 1
• Avoid relying on antibiotics alone for abscesses >4 cm diameter 1
• Do not attempt non-operative management in patients with signs of diffuse peritonitis or hemodynamic instability 1
• Recognize that normal CT scan does not exclude perforation in up to 12% of cases; maintain high clinical suspicion 1
• Timing of source control directly impacts mortality—delayed or incomplete procedures severely worsen outcomes 1, 8

Surgical Approach if Required

• For hemodynamically stable patients, urgent (not emergent) surgery may be delayed up to 24 hours if appropriate antibiotics are given and close monitoring provided 1
• Laparoscopic approach is feasible for many cases with advantages of less invasive access, though may be limited by patient instability or extensive adhesions from recent trauma/surgery 1, 7
• Open surgical drainage via transperitoneal approach is successful in 83% of complex abscesses 4
• Resection of diseased bowel may be necessary depending on underlying pathology 1