What are the differential diagnoses for right lower quadrant (RLQ) pain, taking into account the patient’s age, sex, and reproductive status?

Differential Diagnosis for Right Lower Quadrant Pain

Primary Diagnostic Consideration

Appendicitis is the most common surgical pathology causing RLQ pain, accounting for nearly 50% of emergency department presentations with abdominal pain, and must be the leading consideration in any patient presenting with this complaint. 1

Comprehensive Differential Diagnosis by System

Gastrointestinal Causes

• Right colonic diverticulitis occurs in approximately 8% of patients with RLQ pain and represents the second most common surgical cause after appendicitis 1
• Colitis (infectious, inflammatory, or ischemic) can present with RLQ tenderness and includes conditions such as typhlitis, inflammatory terminal ileitis, and infectious enterocolitis 1
• Inflammatory bowel disease, particularly Crohn's disease affecting the terminal ileum, commonly localizes to the RLQ 2
• Intestinal obstruction (small or large bowel) occurs in approximately 3% of RLQ pain cases and presents with hyperactive bowel sounds, distension, and vomiting 1, 3
• Constipation frequently causes RLQ pain, particularly in younger patients 4
• Gastroenteritis is among the most common CT diagnoses in patients without a final clinical diagnosis 1
• Epiploic appendagitis can mimic appendicitis clinically 1

Genitourinary Causes

• Ureteral stone disease (right-sided urolithiasis) is a common cause that can be definitively diagnosed with CT imaging 1, 2
• Pyelonephritis can present with RLQ pain, especially in young children who may not localize symptoms well 1, 4
• Urinary tract infection should be ruled out with urinalysis in all patients 4

Gynecologic Causes (in females)

• Ovarian torsion must be considered in any female with RLQ pain, regardless of age 4
• Ovarian cyst (ruptured or large) can cause acute RLQ pain 4
• Benign adnexal mass is among the most common CT diagnoses in patients with RLQ pain 1
• Pelvic inflammatory disease should be considered in women of reproductive age 1
• Ectopic pregnancy must be excluded in any woman of reproductive age before attributing RLQ pain to gastrointestinal causes 2
• Pelvic congestion syndrome can present with chronic or acute RLQ pain 1

Vascular Causes

• Mesenteric ischemia should be considered in elderly patients with cardiovascular disease, particularly when pain is out of proportion to physical examination findings 3

Other Causes

• Mesenteric adenitis can mimic appendicitis, often following viral illness, particularly in pediatric patients 4
• Hernia (incarcerated or strangulated) can present with RLQ pain 1
• Body wall pathology including muscle strain or hematoma 1

Age and Sex-Specific Considerations

Pediatric Patients (especially under 5 years)

• Children under 5 years present with atypical symptoms more frequently than older children, making diagnosis particularly challenging, and have higher rates of perforated appendicitis due to delayed diagnosis 4
• Intussusception is more common in younger children, typically presenting with intermittent colicky pain, vomiting, and potentially bloody stools 4
• Classic appendicitis symptoms (periumbilical pain migrating to RLQ, anorexia, nausea, vomiting) are less reliable in children under 5 years 4

Elderly Patients

• Elderly patients frequently lack typical symptoms, have blunted inflammatory responses, and present later with higher complication rates 3, 2
• Colorectal malignancy accounts for 60% of large bowel obstructions in this population, especially with rectal bleeding or weight loss history 3
• Normal laboratory values do not exclude surgical emergencies in elderly patients, as inflammatory markers may be falsely reassuring 3, 2

Women of Reproductive Age

• Always consider gynecologic pathology and pregnancy-related complications before attributing RLQ pain solely to gastrointestinal causes 2
• If gynecologic conditions are the primary concern, refer to specific guidelines for acute pelvic pain in the reproductive age group 1

Critical Clinical Pitfalls to Avoid

• Do not rely on "classic" presentations alone, as many patients, particularly the elderly and very young, present atypically 3, 2
• Normal laboratory values do not exclude surgical emergencies, particularly in elderly patients where tests are nonspecific and may be normal despite serious infection or perforation 3, 2
• Do not wait for complete symptom evolution before imaging, as delays increase perforation risk and morbidity 1
• The negative appendectomy rate based on clinical determination alone without imaging is unacceptably high at 25% 1

Diagnostic Imaging Approach

CT abdomen and pelvis with IV contrast is the mandatory first-line imaging study for adults with nonspecific RLQ pain, achieving 95% sensitivity and 94% specificity for appendicitis while simultaneously identifying alternative diagnoses in 23-45% of cases. 1, 3

Key Imaging Points

• CT frequently identifies causes requiring hospitalization and invasive treatment: 41% of patients with nonappendiceal CT diagnoses were hospitalized, with 22% undergoing surgical or image-guided intervention 1
• Both abdominal and pelvic imaging are necessary, as 7% of abnormalities are located outside the pelvis in regions not covered by focused appendiceal imaging 5
• Ultrasound is the initial imaging modality of choice for pediatric patients due to zero radiation exposure, though MRI is preferred if ultrasound is equivocal 4
• Unenhanced CT can be accurate for suspected urolithiasis with sensitivity and specificity near 100% 1