What is the next step for a patient presenting to the Emergency Room (ER) with 12 hours of right lower abdominal pain, right lower abdominal tenderness, and rebound tenderness?

CT Abdomen and Pelvis with IV Contrast is the Next Step

For a patient presenting with 12 hours of right lower quadrant pain, tenderness, and rebound tenderness, proceed immediately to CT abdomen and pelvis with IV contrast rather than proceeding directly to appendectomy or observation. This approach is strongly recommended despite the classic clinical presentation for appendicitis 1.

Why Imaging Before Surgery is Critical

The negative appendectomy rate without preoperative imaging ranges from 14.7-25%, which is unacceptably high and can be reduced to 1.7-7.7% with preoperative CT imaging 1. Even when clinical findings strongly suggest appendicitis, imaging remains essential because:

• Classic appendicitis symptoms (including fever and leukocytosis) are present in only approximately 50% of actual appendicitis cases 1
• Clinical determination of appendicitis is notoriously poor, with diagnostic accuracy insufficient to rely on examination alone 1, 2
• CT identifies alternative diagnoses in 23.2-45.3% of patients presenting with right lower quadrant pain and classic symptoms, fundamentally changing management 1

Diagnostic Performance of CT

CT abdomen and pelvis with IV contrast demonstrates:

• Sensitivity of 85.7-100% and specificity of 94.8-100% for acute appendicitis 1, 3
• Optimal diagnostic accuracy when using a maximal outer diameter cutoff of 8.2 mm for the appendix 1
• Ability to detect perforation, abscess formation, and periappendiceal inflammation 1

CT without enteral contrast is preferred as it achieves sensitivity of 90-100% and specificity of 94.8-100% while avoiding delays associated with oral contrast administration 1.

Alternative Diagnoses Frequently Detected

CT frequently identifies other conditions mimicking appendicitis, including:

• Right colonic diverticulitis (8% of cases) 1
• Gynecologic pathology (21.6% of alternative diagnoses) 1
• Gastrointestinal conditions (46.0% of alternative diagnoses) 1
• Ureteral stones and intestinal obstruction (3% of cases) 1

Why Other Options Are Inappropriate

Option A (Open Appendectomy): Proceeding directly to surgery without imaging risks unnecessary appendectomy in 14.7-25% of cases and misses alternative diagnoses that require different management 1.

Option D (IV Fluids and 24-Hour Observation): This approach is inappropriate for a patient with established peritoneal signs (rebound tenderness). Observation is only appropriate for low-risk patients without peritoneal signs 1. The presence of rebound tenderness indicates peritoneal irritation requiring definitive diagnosis, not watchful waiting 1.

Management Algorithm After CT

• If appendicitis is confirmed: Proceed to immediate surgical consultation and appendectomy 1, 3
• If perforated appendicitis with abscess (>3 cm): Consider percutaneous catheter drainage followed by delayed interval appendectomy 4, 3
• If CT is negative but clinical suspicion remains high: Consider diagnostic laparoscopy 3
• If alternative diagnosis identified: Manage accordingly based on specific findings 1

Critical Pitfall to Avoid

Do not rely on the absence of documented fever or WBC count to downgrade clinical suspicion. The question states "WBC not mentioned," but this should not delay imaging. Fever is absent in approximately 50% of appendicitis cases, and normal inflammatory markers do not exclude the diagnosis, especially in early presentations 1, 2.