Differential Diagnosis for Lower Quadrant Abdominal Pain
The differential diagnosis for lower quadrant abdominal pain depends critically on laterality, with acute appendicitis being the primary concern for right-sided pain and acute sigmoid diverticulitis for left-sided pain, though numerous gastrointestinal, genitourinary, gynecologic, and vascular conditions must be systematically excluded. 1
Right Lower Quadrant Pain
Primary Diagnostic Considerations
Appendicitis remains the leading surgical emergency, with CT demonstrating 95% sensitivity and 94% specificity for diagnosis 1. However, approximately 50% of patients with right lower quadrant pain have alternative diagnoses that require different management 1.
Common Non-Appendiceal Causes
The most frequently identified alternative diagnoses on CT include 1:
- Benign adnexal masses (gynecologic pathology)
- Gastroenteritis and colitis (infectious or inflammatory)
- Constipation (fecal loading)
- Inflammatory bowel disease (Crohn's terminal ileitis)
- Pelvic congestion syndrome
- Right colonic diverticulitis (8% of cases) 1
- Bowel obstruction (3% of cases) 1
- Ureteral stones (genitourinary pathology) 1
- Infectious enterocolitis (typhlitis, inflammatory terminal ileitis) 1
- Epiploic appendagitis (self-limited fat appendage torsion) 2
- Mesenteric cysts (rare, may mimic appendicitis) 3
Critical Clinical Distinctions
If radicular symptoms with leg radiation and weakness are present, this indicates nerve root involvement rather than visceral pathology—consider lumbar radiculopathy from disc herniation or psoas abscess, which requires different imaging (MRI lumbar spine if CT abdomen/pelvis is negative) 4.
Left Lower Quadrant Pain
Primary Diagnostic Considerations
Acute sigmoid diverticulitis is the most common cause of left lower quadrant pain in adults, with prevalence increasing 50% between 2000-2007 1. Diverticulosis affects 10% of the population at age 40 and 70% or more in elderly patients, with 5-25% developing diverticulitis 1, 5.
Common Alternative Diagnoses
The differential for left lower quadrant pain includes 1, 6:
- Colitis (infectious, ischemic, or inflammatory bowel disease)
- Epiploic appendagitis (self-limited condition mimicking diverticulitis) 1, 2
- Bowel obstruction
- Incarcerated hernia
- Ovarian and fallopian tube pathology (ectopic pregnancy, ovarian torsion, tubo-ovarian abscess)
- Pyelonephritis and urolithiasis (renal colic)
- Perforated colon carcinoma 6
- Abdominal wall pathology 6
Gynecologic Considerations in Reproductive-Age Women
If menstrual irregularities accompany left lower quadrant pain, consider endometriosis and adenomyosis as primary diagnoses rather than diverticulitis, especially in younger patients without fever or leukocytosis 7. Transvaginal ultrasound should be the first-line imaging, with MRI reserved for suspected deep infiltrating endometriosis 7.
Imaging Strategy by Quadrant
Right Lower Quadrant
CT abdomen and pelvis with IV contrast is the preferred initial imaging modality (rated 8/9 "usually appropriate" by the American College of Radiology), providing high diagnostic yield for both appendicitis and alternative diagnoses 1. This imaging altered diagnosis in 43 of 67 patients (64%) suspected of having appendicitis and changed management plans in 42% of all patients with abdominal pain 1.
- In patients receiving non-appendiceal CT diagnoses, 41% required hospitalization and 22% underwent surgical or image-guided intervention 1
- Noncontrast CT has 92.7% sensitivity and 96.1% specificity for appendicitis if contrast is contraindicated 1
- Pelvic ultrasonography is preferred in women of childbearing age to evaluate gynecologic pathology first 1
Left Lower Quadrant
CT abdomen and pelvis with IV contrast is the imaging modality of choice (rated 8/9 "usually appropriate"), with sensitivity greater than 95% for detecting diverticulitis and 98% diagnostic accuracy overall 1, 5. CT identifies disease severity, complications (perforation, abscess, fistula), and alternative diagnoses 1.
- Unenhanced CT has similar accuracy (64-68%) to contrast-enhanced CT (68-71%) in elderly patients and is appropriate for suspected urolithiasis with near 100% sensitivity 1
- MRI has 86-94% sensitivity and 88-92% specificity for diverticulitis but is more expensive and time-consuming 1
- Ultrasonography with graded compression is operator-dependent and limited in obese patients, though effective when performed by experienced operators 1, 6
Critical Pitfalls to Avoid
Do not assume appendicitis in right lower quadrant pain without considering the 50% of cases with alternative diagnoses that may require different management (medical vs. surgical) 1. Of patients with non-appendiceal diagnoses, 41% require hospitalization and 22% need intervention 1.
Do not diagnose diverticulitis clinically in younger patients with menstrual correlation of symptoms—this pattern strongly suggests gynecologic pathology (endometriosis/adenomyosis) requiring transvaginal ultrasound rather than CT 7.
Do not miss neurological causes when radicular symptoms and weakness accompany right lower quadrant pain—this indicates nerve root involvement or psoas abscess rather than appendicitis, requiring urgent MRI lumbar spine if CT abdomen/pelvis is negative 4.
Do not rely on conventional radiography for lower quadrant pain evaluation—it has limited diagnostic value and rarely changes management except for suspected bowel obstruction, perforation, or urinary calculi 1.
Do not delay imaging in patients with fever, leukocytosis, peritoneal signs, or progressively worsening pain—these red flags mandate urgent CT to exclude life-threatening complications (perforation, abscess, ischemia) 1, 5.