What is the appropriate diagnosis and treatment for left lower quadrant pain in an adult male without dysuria and constipation?

Left Lower Quadrant Pain in Adult Male Without Dysuria and Constipation

Order CT abdomen and pelvis with IV contrast immediately—this is the single most important diagnostic test with 98% accuracy and will guide all subsequent management decisions. 1, 2

Diagnostic Approach

Most Likely Diagnosis

• Acute diverticulitis is the leading cause of left lower quadrant pain in adult males, affecting 5-25% of patients with diverticulosis, with prevalence increasing substantially in older patients (70% or more have diverticulosis). 1, 2
• Clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68%, making imaging essential rather than optional. 2
• The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases, so absence of fever does not exclude the diagnosis. 2

Critical Alternative Diagnoses to Consider

• Perforated colon cancer can perfectly mimic diverticulitis clinically and must be actively excluded. 2, 3
• Other important differentials include colitis, inflammatory bowel disease, epiploic appendagitis, bowel obstruction, hernia, pyelonephritis, and urolithiasis. 1
• Rare but critical: Appendicitis with redundant cecum or situs inversus can present with left lower quadrant pain. 4, 5, 6

Imaging Strategy

First-Line Imaging

• CT abdomen and pelvis with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and should be ordered immediately. 1, 2
• IV contrast improves detection of bowel wall pathology, pericolic abnormalities, vascular pathology, and intra-abdominal fluid collections. 1, 2
• CT provides comprehensive evaluation of all abdominal organs in a single examination and identifies alternative diagnoses. 2

Key CT Findings to Identify

• Intestinal wall thickening with pericolonic fat stranding indicates diverticulitis. 2
• Pericolonic lymphadenopathy >1 cm is the critical distinguishing feature suggesting malignancy rather than diverticulitis. 2, 3
• Extraluminal air or intra-abdominal fluid indicates perforation requiring urgent surgical consultation. 2
• Abscess size must be measured carefully as it determines drainage strategy (<4 cm vs ≥4 cm). 2

Alternative Imaging

• Unenhanced CT is acceptable when IV contrast is contraindicated, though less accurate for detecting abscesses (rated 6/9). 1, 2
• Ultrasound is operator-dependent and limited in obese patients but can reduce unnecessary CT examinations. 2, 7
• MRI is not useful for initial evaluation—it is less sensitive for extraluminal air and urinary calculi, more time-consuming, and more subject to motion artifact. 1

Management Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Fistula)

• Conservative management without antibiotics is appropriate for immunocompetent patients. 2
• Clear liquid diet advancement and oral analgesics for pain control. 2
• Antibiotics only for immunocompromised or elderly patients: Ertapenem 1 g q24h or Eravacycline 1 mg/kg q12h for maximum 7 days. 2

Complicated Diverticulitis with Small Abscess (<4 cm)

• Antibiotic therapy alone for 7 days without drainage. 2
• Use Ertapenem 1 g q24h or Eravacycline 1 mg/kg q12h. 2

Complicated Diverticulitis with Large Abscess (≥4 cm)

• Percutaneous drainage combined with antibiotics for 4 days in immunocompetent, non-critically ill patients. 2, 8
• Stop antibiotics at 4 days if source control is adequate. 2
• Continue up to 7 days in immunocompromised or critically ill patients, guided by clinical response. 2

Perforation with Peritonitis or Free Air

• Emergent surgical consultation is mandatory. 2, 3
• If septic shock is present, use Meropenem 1 g q6h by extended infusion, Doripenem 500 mg q8h by extended infusion, or Imipenem/cilastatin 500 mg q6h by extended infusion. 2

Critical Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is required if any of the following are present:

• Fever with inability to pass gas or stool. 2, 3
• Severe abdominal tenderness with guarding or rebound tenderness (peritonitis). 2, 3
• Signs of shock (hypotension, tachycardia, altered mental status). 2, 3
• Vomiting or bloody stools. 2
• Progressively worsening pain over several days. 2

Common Pitfalls to Avoid

Do Not Miss Colon Cancer

• Pericolonic lymphadenopathy >1 cm with or without pericolonic edema strongly suggests malignancy rather than diverticulitis. 2, 3
• Colonoscopy is mandatory if lymphadenopathy >1 cm or atypical features are present to exclude malignancy. 3
• Routine colonoscopy after CT-confirmed diverticulitis is not warranted except for age-appropriate screening, unless abscess, perforation, or fistula is present. 2

Do Not Overuse Antibiotics

• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes. 2
• If signs of infection persist beyond 7 days, obtain repeat imaging to assess for inadequate source control rather than continuing antibiotics empirically. 2

Do Not Rely on Clinical Diagnosis Alone

• Clinical diagnosis has a 34-68% misdiagnosis rate, making CT essential. 2, 3
• The classic triad is present in only 25% of cases, so atypical presentations are common. 2

Consider Rare Anatomic Variants

• Appendicitis with redundant cecum or situs inversus can present with left lower quadrant pain and should be identified on CT. 4, 5, 6
• Subtle indicators of situs inversus may be missed on physical examination but are immediately apparent on CT. 4