Why is a CT (computed tomography) abdomen and pelvis with and without contrast a good diagnostic approach for an adult patient with a history of diverticulitis, status post (s/p) sigmoid colectomy, presenting with right lower quadrant (RLQ) pain?

CT Abdomen/Pelvis With and Without Contrast for Post-Sigmoid Colectomy RLQ Pain

In a patient with prior sigmoid colectomy for diverticulitis presenting with RLQ pain, CT abdomen/pelvis with IV contrast is the optimal imaging modality because it provides comprehensive evaluation for both recurrent diverticulitis (which can occur in remaining colon segments at 4.2% rate) and alternative diagnoses including right-sided diverticulitis, abscess formation, anastomotic complications, and other causes of RLQ pain with 95% sensitivity. 1, 2

Why CT With Contrast is the Gold Standard

Diagnostic Accuracy and Comprehensive Evaluation

• CT has 95% sensitivity and 94% specificity for detecting acute inflammatory conditions in the abdomen, making it superior to all other imaging modalities for evaluating RLQ pain 1
• The modality excels at identifying both appendiceal and non-appendiceal pathology, with studies showing CT diagnosis concordant with clinical diagnosis in 94.3% of cases for non-appendicitis conditions 1
• IV contrast enhancement is critical because it improves detection of bowel wall abnormalities, solid organ injuries, vascular pathology, and intraabdominal fluid collections 3

Specific Relevance to Post-Colectomy Patients

Recurrent Diverticulitis Risk

• Recurrent diverticulitis occurs in 4.2% of patients after sigmoid colectomy, with mean time to recurrence of 55 months (range 6-109 months), and all recurrences are confirmed by CT scan 2
• The remaining colon (including right colon, transverse colon, and descending colon) remains at risk for new diverticular disease 4, 5

Right-Sided Diverticulitis Detection

• Right-sided diverticulitis presents identically to appendicitis and is increasingly recognized as a cause of RLQ pain, particularly in older patients 6, 7
• CT findings of right colon diverticulitis include thickening of the intestinal wall and pericolonic inflammation, present in 100% of cases, with associated diverticular abscess identified correctly preoperatively in all cases 7
• Right colonic diverticulitis and obstruction account for 8% and 3% respectively of RLQ pain presentations 1

Complication Detection

• CT accurately identifies abscess formation (present in 16% of diverticulitis cases), free air (10%), and fistula formation (1%) 4
• The modality has 96-98% accuracy for detecting complications of diverticulitis including abscess extent, which directly determines whether medical versus surgical management is appropriate 1
• CT detects unsuspected carcinoma in 7% of patients presenting with presumed diverticulitis, a critical finding that changes management entirely 4

The "With and Without" Protocol Advantage

Enhanced Lesion Characterization

• Oral and/or colonic contrast may be helpful for bowel luminal visualization when combined with IV contrast, allowing differentiation between bowel wall thickening and intraluminal contents 1
• The dual-phase protocol (without and with IV contrast) provides superior characterization of abscesses versus phlegmon, which determines need for percutaneous drainage versus medical management 1

Anastomotic Assessment

• Non-contrast images establish baseline attenuation of tissues, while post-contrast images reveal enhancement patterns that identify anastomotic leaks, strictures, or inflammatory changes at the surgical site 1

Alternative Diagnoses Effectively Evaluated

High-Yield Differential for RLQ Pain Post-Colectomy

• Infectious enterocolitis (typhlitis, inflammatory terminal ileitis): 41% of patients with non-appendiceal CT diagnoses require hospitalization and 22% need surgical or image-guided intervention 1
• Ureteral stone disease: CT without contrast component is optimal for stone detection 1
• Inflammatory bowel disease: CT enterography characteristics visible on standard CT 1
• Benign adnexal masses, pelvic congestion syndrome, constipation, colitis: most common CT diagnoses in patients with RLQ pain when appendicitis is excluded 1

Clinical Impact on Management

Triage and Treatment Planning

• CT findings directly determine hospitalization need: 41% hospitalization rate when CT identifies pathology versus only 14% when CT is negative 1, 8
• Surgical or interventional procedures required in 22% when CT positive versus only 4% when CT negative, demonstrating the modality's critical role in resource allocation 1, 8
• CT facilitates selection of patients for medical rather than surgical therapy by revealing presence and extent of abscess formation 1

Avoiding Pitfalls

• Plain radiographs are extremely limited in evaluating diverticulitis complications, significantly less sensitive than CT for detecting small amounts of free air or abscess 1
• Ultrasound misdiagnoses 17% of uncomplicated diverticulitis and 79% of complicated diverticulitis, with inability to penetrate extensive soft tissue or air-filled structures 1
• Contrast enema is less sensitive for extracolonic complications including abscesses when compared to CT 1

Key Clinical Considerations

When Imaging May Not Be Necessary

• Patients with classic presentation and no suspected complications may not require imaging if they have typical symptoms of uncomplicated recurrent diverticulitis 1
• However, in a post-surgical patient with RLQ pain (atypical location), imaging is essential because the differential is broad and includes surgical complications 1

Radiation Exposure Context

• While CT involves radiation exposure (☢☢☢☢), the diagnostic yield justifies the risk when surgical history and atypical pain location create diagnostic uncertainty 1
• The high negative predictive value prevents unnecessary surgery: among patients with negative CT showing only stool, only 14% require hospitalization 8