What are the appropriate diagnostic steps and treatment options for a 40-year-old male presenting with lower abdominal pain?

Lower Abdominal Pain in a 40-Year-Old Male

Immediate Diagnostic Approach

Order CT abdomen and pelvis with IV contrast as the first-line imaging study for this patient. This is the most accurate diagnostic test with 98% diagnostic accuracy and will guide all subsequent management decisions 1.

Clinical Assessment Priority

Before imaging, rapidly assess for life-threatening conditions:

• Check vital signs for shock indicators (hypotension, tachycardia, altered mental status) suggesting perforation, ruptured aneurysm, or mesenteric ischemia 2
• Evaluate pain characteristics: Pain out of proportion to physical exam findings is the hallmark of mesenteric ischemia, which carries 30-90% mortality 2
• Assess for peritonitis: Diffuse tenderness, guarding, rebound tenderness, or absent bowel sounds indicate possible perforation requiring emergent surgery 1
• Document fever and leukocytosis: The classic triad of left lower quadrant pain, fever, and leukocytosis suggests diverticulitis, though present in only 25% of cases 1

Why CT with IV Contrast is Essential

CT abdomen/pelvis with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and provides critical advantages 3, 1:

• Detects complications (abscess, perforation, fistula, obstruction) that determine surgical versus medical management 1
• Identifies alternative diagnoses (appendicitis, bowel obstruction, urolithiasis, malignancy) that present similarly 3
• Changes the leading diagnosis in 51% of patients and admission decisions in 25% of cases 3
• Reduces hospital admissions by >50% through accurate risk stratification 1

Common Diagnostic Pitfalls to Avoid

Do not rely on clinical assessment alone—misdiagnosis rates range from 34-68% without imaging 1. The most common causes of lower abdominal pain in this age group include 3:

• Diverticulitis (most common in left lower quadrant)
• Appendicitis (most common overall—one-third of all cases)
• Small bowel obstruction
• Urolithiasis
• Colitis/inflammatory bowel disease

Watch for cancer mimicking diverticulitis: Pericolonic lymph nodes >1 cm with or without pericolonic edema on CT suggest malignancy rather than benign inflammation 1.

Treatment Algorithm Based on CT Findings

If Uncomplicated Diverticulitis (No Abscess/Perforation)

Conservative management without antibiotics is appropriate for immunocompetent patients 1:

• Outpatient management with clear liquid diet advancing as tolerated
• No antibiotics needed unless immunocompromised or elderly 1
• Follow-up in 2-3 days to ensure clinical improvement

If Complicated Diverticulitis with Small Abscess (<3-4 cm)

Antibiotic therapy alone for 7 days 1:

• Ertapenem 1 g IV q24h or Eravacycline 1 mg/kg IV q12h 1
• Admission for IV antibiotics if unable to tolerate oral intake
• Outpatient management possible if clinically stable

If Complicated Diverticulitis with Large Abscess (>3-4 cm)

Percutaneous drainage plus antibiotics for 4 days 1:

• Interventional radiology consultation for CT-guided drainage
• Same antibiotic regimens as above 1
• Admission required

If Septic Shock Present

Escalate to carbapenem therapy 1:

• Meropenem 1 g IV q6h by extended infusion, or
• Doripenem 500 mg IV q8h by extended infusion, or
• Imipenem/cilastatin 500 mg IV q6h by extended infusion 1
• ICU admission and surgical consultation

If Appendicitis Diagnosed

Admission and surgical consultation required 4. Appendectomy remains standard treatment, though antibiotics-first approach may be considered in select cases of uncomplicated appendicitis 3.

Red Flags Requiring Emergency Surgery

Immediate surgical consultation if any of the following 1:

• Signs of peritonitis (diffuse tenderness, guarding, rigidity)
• Free air on CT indicating perforation
• Complete bowel obstruction with inability to pass gas/stool
• Hemodynamic instability despite resuscitation
• Clinical deterioration despite appropriate medical management

Special Considerations

Contrast Contraindications

If IV contrast is contraindicated (severe renal impairment, contrast allergy):

• CT without contrast is acceptable (rated 6/9) but less accurate for detecting abscesses 3, 1
• Unenhanced CT showed similar accuracy (64-68%) to contrast-enhanced CT (68-71%) in elderly patients with acute abdominal pain 3
• The crucial resuscitation with crystalloids and antibiotics minimizes contrast-induced acute kidney injury risk 3

When Ultrasound May Be Considered

Ultrasound is operator-dependent and less comprehensive but may reduce unnecessary CT examinations 3:

• Useful if renal colic strongly suspected (though CT remains gold standard)
• Limited by obesity and bowel gas
• Cannot reliably exclude surgical pathology

Follow-Up Imaging

Routine colonoscopy after CT-confirmed uncomplicated diverticulitis is NOT indicated except for 1:

• Age-appropriate colon cancer screening not yet performed
• Abnormal pericolonic lymph nodes >1 cm
• Luminal mass visualized
• Uncertain diagnosis (inflammatory bowel disease, ischemic colitis)