What is the differential diagnosis for a patient presenting with right lower quadrant pain, considering their age, sex, and medical history, including previous abdominal surgeries or inflammatory bowel disease?

Right Lower Quadrant Pain: Differential Diagnosis

The differential diagnosis for right lower quadrant (RLQ) pain must prioritize appendicitis first, but systematically consider gastrointestinal, genitourinary, gynecologic, and vascular etiologies, with CT abdomen/pelvis with IV contrast as the mandatory diagnostic tool achieving 95% sensitivity and 94% specificity. 1

Primary Surgical Emergency

• Appendicitis is the most common surgical pathology causing RLQ pain, accounting for nearly 50% of emergency department presentations with abdominal pain and representing the leading diagnosis requiring operative management. 2, 3
• Clinical examination alone has an unacceptably high negative appendectomy rate of up to 25%, making imaging essential rather than optional. 1, 3
• Perforated appendicitis carries high morbidity and mortality if diagnosis is delayed, though imaging does not increase perforation rates from any introduced delays. 1, 3

Gastrointestinal Causes Beyond Appendicitis

• Right colonic diverticulitis accounts for approximately 8% of RLQ pain cases and is particularly important in older adults. 1, 2
• Intestinal obstruction (small or large bowel) is present in approximately 3% of cases and presents with hyperactive bowel sounds, distension, and vomiting. 1, 2
• Inflammatory bowel disease (Crohn's disease affecting the terminal ileum) commonly causes RLQ pain and can be identified on CT imaging. 2
• Colitis (infectious, inflammatory, or ischemic) can present with RLQ tenderness and must be differentiated from appendicitis. 1, 2
• Infectious enterocolitis including typhlitis and inflammatory terminal ileitis can present with RLQ pain. 1, 3

Genitourinary Causes

• Ureteral stone (right-sided nephrolithiasis) is a common cause of RLQ pain that can be definitively diagnosed with CT imaging. 1, 2, 3

Gynecologic Considerations

• Ectopic pregnancy must be excluded in all women of reproductive age before imaging, with beta-hCG testing being mandatory. 3
• Gynecologic pathology should always be considered in women of reproductive age before attributing RLQ pain solely to gastrointestinal causes. 2
• For patients where gynecologic conditions are the primary concern, refer to specific pelvic pain guidelines. 1

Additional Diagnostic Considerations

• Benign adnexal mass, gastroenteritis, constipation, and pelvic congestion syndrome were the most common CT diagnoses in patients without a final clinical diagnosis. 1
• Colorectal malignancy accounts for 60% of large bowel obstructions, especially with rectal bleeding or weight loss history. 4
• Mesenteric ischemia should be considered in elderly patients with cardiovascular disease and pain out of proportion to examination. 4

Mandatory Diagnostic Approach

• CT abdomen and pelvis with IV contrast is the single mandatory imaging study, achieving 95% sensitivity and 94% specificity for appendicitis while simultaneously identifying alternative diagnoses in 23-45% of cases. 1, 2, 3
• CT frequently identifies conditions requiring hospitalization and invasive treatment: 41% of patients with nonappendiceal CT diagnoses were hospitalized, with 22% undergoing surgical or image-guided intervention. 1
• In patients with nonappendiceal diagnoses, CT diagnosis was concordant with clinical diagnosis in 94.3% of cases. 1

Critical Clinical Pitfalls to Avoid

• Do not rely on clinical examination alone as clinical determination tools like the Alvarado score have not improved diagnostic accuracy and show mixed results for guiding CT use. 1, 3
• Do not wait for "classic" presentations, as elderly patients frequently lack typical symptoms, have blunted inflammatory responses, and present later with higher complication rates. 2, 4
• Normal laboratory values do not exclude surgical emergencies, particularly in elderly patients where inflammatory markers may be falsely reassuring. 1, 2, 4
• Always obtain pregnancy testing before any imaging in women of reproductive age to avoid delayed diagnosis of ectopic pregnancy and unnecessary radiation exposure. 3
• Do not use ultrasound as first-line imaging in adults with nonspecific RLQ pain, as it has 20-81% non-visualization rates and equivocal results require CT anyway, causing diagnostic delay. 4

Special Clinical Scenarios

When hyperactive bowel sounds are present with RLQ tenderness, the differential diagnosis shifts to prioritize:

• Small bowel obstruction (most likely given hyperactive sounds) 4
• Early appendicitis 4
• Right-sided colonic diverticulitis 4
• Colorectal malignancy 4
• Mesenteric ischemia 4