What is the appropriate initial workup for a patient presenting with left lower quadrant abdominal pain?

Workup for Left Lower Quadrant Abdominal Pain

CT abdomen and pelvis with IV contrast is the most appropriate initial imaging study for adults presenting with left lower quadrant pain, as it provides superior diagnostic accuracy (98%) for diverticulitis—the most common cause—and effectively identifies alternative diagnoses and complications. 1

Initial Clinical Assessment

Key Clinical Features to Evaluate

• Classic diverticulitis triad: Left lower quadrant pain, fever, and leukocytosis (present in only ~25% of cases) 1
• Severity indicators: Abdominal distention, rigidity, peritoneal signs 2
• Alternative diagnoses: Consider renal colic, urinary tract infection, gynecologic disorders, epiploic appendicitis, perforated carcinoma, and inflammatory bowel disease 3

Laboratory Workup

Order the following tests initially:

• Complete blood count 2, 4
• Basic metabolic panel 2
• C-reactive protein 2
• Urinalysis 2, 4
• Pregnancy test in women of reproductive age 4

Important caveat: Clinical assessment alone has a misdiagnosis rate of 34-68% for diverticulitis, making imaging critical in most cases 1

Imaging Strategy

First-Line Imaging: CT Abdomen and Pelvis with IV Contrast

This is rated as "usually appropriate" (rating 8/9) by the American College of Radiology 1

Key advantages:

• Diagnostic accuracy of 98% for diverticulitis 1
• Identifies complications (perforation, abscess, fistula, obstruction) that determine surgical vs. medical management 1
• Accurately diagnoses alternative pathology 1
• Can reduce hospital admissions by >50% when uncomplicated disease is confirmed 1
• Guides triage between inpatient and outpatient management 1

Technical considerations:

• IV contrast improves detection of subtle bowel wall abnormalities and abscesses 1
• Unenhanced CT is acceptable if IV contrast is contraindicated, though less sensitive 1
• Oral or colonic contrast may help with bowel luminal visualization but is not mandatory 1
• Low-dose CT (50-90% radiation reduction) maintains diagnostic accuracy 1

Alternative Imaging Modalities

Ultrasound (transabdominal with graded compression):

• May be appropriate (rating 4-6/9) but less commonly used in the United States for nongynecologic left lower quadrant pain 1
• Can reduce unnecessary CT examinations by identifying patients without surgical abdomen 1
• Limited by operator dependency and difficulty in obese patients 1

Pelvic ultrasound (transvaginal):

• Use as initial imaging in premenopausal women when gynecologic pathology is suspected (ectopic pregnancy, ovarian torsion, pelvic inflammatory disease) 1, 4
• Gynecologic and nongynecologic causes can present identically in this population 1

MRI abdomen and pelvis:

• Not useful for initial evaluation—less sensitive for free air and urinary calculi, more time-consuming, subject to motion artifacts 1
• Diagnostic accuracy likely inferior to CT with insufficient evidence to support routine use 1
• Reserved for pregnant patients when ultrasound is inconclusive 4

Plain radiography:

• Usually not appropriate (rating 4/9) as initial test 1
• CT is more sensitive and specific for all relevant pathology 1

Contrast enema:

• Not useful as initial imaging (rating 5/9) 1
• Less sensitive than CT and rarely used 1

When Imaging May Not Be Required

Consider empiric treatment without imaging in highly selected patients with ALL of the following: 1

• Typical symptoms of diverticulitis
• Prior documented history of diverticulitis with similar presentation
• No evidence of complications on clinical examination
• Mild symptoms suitable for outpatient management

However, there is a strong trend toward imaging even in these patients to confirm diagnosis, assess disease extent, and detect complications that would alter management 1

Special Populations

Women of reproductive age:

• Start with pelvic ultrasound if gynecologic etiology is suspected 1, 4
• Pregnancy test is mandatory before any imaging 4

Elderly patients:

• May present with atypical symptoms 5
• Higher risk of complicated diverticulitis requiring more aggressive imaging and management 1

Critical Pitfall to Avoid

Do not rely on clinical assessment alone—the misdiagnosis rate is 34-68% for diverticulitis, and complications requiring intervention (abscess ≥3 cm, perforation, fistula) fundamentally change management from outpatient antibiotics to drainage or surgery 1