Should I skip contrast‑enhanced CT abdomen/pelvis and go straight to colonoscopy in a 61‑year‑old woman with a three‑year history of left lower quadrant pain, nausea, constipation, and negative initial work‑up (ultrasound, fecal immunochemical test, celiac serology, Helicobacter pylori testing, routine labs)?

No—Proceed with Contrast-Enhanced CT Abdomen/Pelvis Before Colonoscopy

In a 61-year-old woman with chronic left lower quadrant pain and negative initial work-up, you should obtain contrast-enhanced CT abdomen/pelvis first rather than proceeding directly to colonoscopy. This approach prioritizes detection of life-threatening conditions (perforation, abscess, malignancy) and guides appropriate management before any endoscopic intervention.

Why CT Takes Priority

CT Provides Critical Diagnostic Information That Colonoscopy Cannot

• Contrast-enhanced CT is the most accurate initial imaging test for left lower quadrant pain, with 98% overall diagnostic accuracy for conditions like diverticulitis 1
• IV contrast specifically improves detection of bowel wall abnormalities, abscesses, perforation, and vascular pathology that would be completely missed by colonoscopy 2, 1
• CT evaluates the entire abdomen and pelvis for alternative diagnoses including gynecologic pathology, urologic conditions, and mesenteric ischemia—all of which can present with left lower quadrant pain 2

CT Identifies Complications That Make Colonoscopy Dangerous

• CT can detect perforation, abscess, or severe inflammation where colonoscopy would be contraindicated and potentially catastrophic 2
• Small-volume pericolic air (<5 cm) can be treated medically, whereas spilled feces requires surgical management—information only CT provides 2
• CT identifies strictures and fistulas that may require surgical rather than endoscopic management 2

The Three-Year History Changes Nothing About This Algorithm

• Chronic symptoms do not exclude acute complications—diverticulitis can develop insidiously, and colorectal cancer can present with years of vague symptoms 2
• The negative FIT test reduces but does not eliminate cancer risk, particularly for right-sided lesions or non-bleeding tumors 2
• CT will determine whether colonoscopy is even safe to perform by ruling out perforation risk 2, 1

Optimal CT Protocol

Use IV Contrast Unless Contraindicated

• The American College of Radiology rates CT with IV contrast as 8 out of 9 (usually appropriate) versus only 6 out of 9 for non-contrast CT for suspected diverticulitis 1
• IV contrast improves characterization of bowel wall pathology, pericolic abnormalities, and fluid collections—critical for distinguishing abscess from adjacent bowel 2, 1
• Non-contrast CT has "poorer performance" and misses the hyperenhancing inflammatory changes that define active disease 3

Oral Contrast Is Optional

• Many institutions no longer routinely use oral contrast due to delays in scan acquisition without clear diagnostic advantage 2
• Multiplanar reformations on modern CT can improve diagnostic confidence without oral contrast 2
• If oral contrast is used, combining it with IV contrast is superior to unenhanced CT with oral contrast for characterizing complications 2

Request Low-Dose Protocol

• Low-dose CT achieves 75-90% radiation reduction while maintaining similar sensitivity and specificity for diverticulitis 1

When Colonoscopy Follows CT

CT Findings Determine Colonoscopy Timing

• If CT shows uncomplicated diverticulosis or mild diverticulitis, colonoscopy can be scheduled electively after inflammation resolves (typically 6-8 weeks) 2
• If CT shows a mass or stricture, colonoscopy becomes essential for tissue diagnosis 2, 4
• If CT shows abscess, perforation, or severe inflammation, colonoscopy is contraindicated until complications resolve 2

CT May Reveal Pathology Beyond Colonoscopy's Reach

• CT can detect synchronous lesions proximal to obstructing masses in endoscopically inaccessible regions 4
• CT evaluates extraluminal tumor extension and lymph node involvement for surgical planning 4

Common Pitfalls to Avoid

Do Not Skip Imaging Based on Chronicity

• Misdiagnosis based on clinical assessment alone occurs in 34-68% of diverticulitis cases, even with the classic triad of left lower quadrant pain, fever, and leukocytosis (present in only 25% of cases) 2
• Colorectal cancer can present with years of vague abdominal symptoms before becoming clinically obvious 5, 4

Do Not Rely on Alternative Imaging

• Ultrasound is operator-dependent, limited by body habitus, and has significantly lower sensitivity for alternative diagnoses 1
• MRI is not appropriate for acute evaluation due to limited availability, difficulty detecting extraluminal air, and motion artifacts 1
• Plain radiography is extremely limited, detecting only large amounts of free air while missing small perforations 1

Do Not Order Contrast Enema

• Contrast enema only shows secondary effects of inflammation, misses extraluminal abnormalities like abscesses, and increases perforation risk in acute diverticulitis 1

Clinical Algorithm

1. Order contrast-enhanced CT abdomen/pelvis (with IV contrast, oral contrast optional, request low-dose protocol) 2, 1

2. If CT shows:

   • Uncomplicated diverticulosis/mild diverticulitis: Schedule colonoscopy in 6-8 weeks after inflammation resolves 2
   • Mass, stricture, or suspicious lesion: Proceed with colonoscopy for tissue diagnosis 2, 4
   • Abscess, perforation, or severe inflammation: Treat medically or surgically first; defer colonoscopy 2
   • Alternative diagnosis (ovarian pathology, urolithiasis, etc.): Manage accordingly; colonoscopy may be unnecessary 2

3. If CT is completely normal, consider functional disorder (IBS) or proceed with colonoscopy if age-appropriate screening is due 2