How should I evaluate and manage a patient with acute left lower‑quadrant pain radiating to the anterior leg?

Evaluation and Management of Acute Left Lower Quadrant Pain Radiating to the Anterior Leg

Immediate Diagnostic Approach

Order CT abdomen and pelvis with IV contrast as your initial imaging study—this is the gold standard for evaluating acute left lower quadrant pain and will identify life-threatening complications including perforation, abscess, and alternative diagnoses that ultrasound frequently misses. 1, 2

Key Clinical Assessment Points

Before imaging, rapidly assess for these critical features:

• Fever and leukocytosis: Present in only ~25% of diverticulitis cases, but when present strongly suggest inflammatory/infectious process 1, 3
• Ability to pass gas/stool: Inability suggests obstruction requiring urgent intervention 4
• Peritoneal signs: Rebound tenderness and guarding indicate possible perforation with 82.5% sensitivity for peritonitis 5
• Hemodynamic stability: Signs of shock mandate immediate surgical consultation 4

Important caveat: Clinical examination alone has a misdiagnosis rate of 34-68% for diverticulitis, making imaging essential rather than optional 1, 2

Why CT with IV Contrast is Superior

• Detects small-volume extraluminal air indicating perforation that plain radiography misses—this finding has significant surgical implications and mortality risk 1, 2
• Identifies complications requiring intervention: abscesses ≥3 cm (for drainage), fistulas, obstruction, or free perforation (for surgery) 1
• Reveals alternative diagnoses in 49% of cases with nonlocalized pain, including malignancy, vascular pathology, urologic conditions, and gynecologic disease 5
• Superior sensitivity: 81% for CT versus 61% for ultrasound (P = 0.048) in head-to-head comparison 1

Special Consideration: The Radiating Leg Pain

The radiation to the anterior leg is atypical for uncomplicated diverticulitis and raises concern for:

• Psoas abscess from perforated diverticulitis tracking along tissue planes—CT will demonstrate this 6, 7
• Nerve involvement from inflammatory mass effect on lumbosacral plexus
• Alternative diagnosis such as nephrolithiasis or gynecologic pathology with referred pain

When Imaging May Not Be Required

You can consider treating empirically without imaging only if ALL of the following criteria are met 1, 3:

• Prior documented history of diverticulitis with identical symptoms
• Well-appearing patient with controlled pain
• Able to tolerate oral intake
• No fever, no peritoneal signs, no obstruction symptoms
• No immunocompromise or severe comorbidities
• Reliable for close follow-up

However, given the atypical radiation to the leg in this case, imaging is strongly recommended even if other criteria suggest uncomplicated disease.

Alternative Imaging Modalities: When and Why Not

Ultrasound

• Limited role in the United States for initial evaluation of suspected diverticulitis 1
• Sensitivity 77-98%, specificity 80-99%, but highly operator-dependent and body habitus-limited 1
• Use transvaginal ultrasound first only in premenopausal women when gynecologic pathology (ectopic pregnancy, PID) is the primary clinical suspicion 1
• May miss critical findings like small perforations and alternative diagnoses 1, 2

Plain Radiography

• Not useful as initial test—CT is far more sensitive for all relevant pathology 1
• Can identify large-volume free air or obstruction, but CT detects these with higher sensitivity 1

MRI

• Not appropriate for acute evaluation 1
• Less sensitive for extraluminal air and urinary calculi
• More time-consuming (problematic in acute pain)
• More susceptible to motion artifact in symptomatic patients 1
• May have role in follow-up or when CT equivocal (sensitivity 86-94%, specificity 88-92%) 1, 4

Contrast Enema

• No role in initial evaluation of acute left lower quadrant pain 1

Management Algorithm Based on CT Findings

Uncomplicated Diverticulitis (no abscess, no perforation, no obstruction)

• Select patients may not require antibiotics: well-appearing, pain controlled, tolerating oral intake, immunocompetent, able to follow up 3
• If antibiotics used, target facultative and obligate anaerobic gram-negative bacilli 7

Complicated Diverticulitis

• Abscess ≥3 cm: CT-guided percutaneous drainage plus antibiotics 1, 7
• Free perforation with peritonitis: Immediate surgical consultation, broad-spectrum antibiotics, NPO status 1, 5
• Obstruction: Nasogastric decompression, surgical evaluation 5

Alternative Diagnoses to Consider

• Perforated colon cancer: Look for pericolonic lymphadenopathy >1 cm without mesenteric edema 1, 4
• Psoas abscess: Especially relevant given leg radiation 6
• Nephrolithiasis/pyelonephritis: CT without contrast more sensitive for stones 1
• Gynecologic pathology: In premenopausal women, consider pelvic ultrasound if CT equivocal 1

Critical Pitfalls to Avoid

• Don't rely on normal inflammatory markers: 39% of patients with complicated diverticulitis have CRP <175 mg/L 2
• Don't assume diverticulitis in elderly patients: Only 50% have lower quadrant pain, only 17% have fever—atypical presentations are common 2
• Don't miss the mortality risk: Increases dramatically with age (1.6% in <65 years, 9.7% in 65-79 years, 17.8% in >80 years) 2
• Don't order colonoscopy acutely: Colonic distention increases perforation risk in acute diverticulitis 1

Follow-Up Considerations

• Colonoscopy timing: Not routinely needed after CT-confirmed uncomplicated diverticulitis, except for age-appropriate screening 1
• Higher cancer risk when abscess, perforation, or fistula identified—consider colonoscopy 6-8 weeks after resolution 1
• Red flags for repeat imaging: New pericolonic lymphadenopathy >1 cm, weight loss, anemia, change in bowel habits 4