What are the possible causes of left lower quadrant pain?

Causes of Left Lower Quadrant Pain

Acute sigmoid diverticulitis is the most common cause of left lower quadrant pain in adults, especially those over 50 years old, but CT imaging with IV contrast is mandatory because clinical examination alone misdiagnoses 34-68% of cases. 1

Primary Differential Diagnosis

Gastrointestinal Causes (Most Common)

• Acute diverticulitis of the sigmoid or descending colon is the leading etiology, with prevalence increasing by 50% between 2000-2007. 1, 2
• Colitis (infectious, ischemic, or inflammatory) presents with similar pain patterns and requires CT differentiation. 1, 2
• Inflammatory bowel disease (Crohn's disease or ulcerative colitis) may show skip lesions or multi-segment bowel wall thickening on imaging. 1
• Epiploic appendagitis appears as a pericolic fatty mass with hyperattenuated rim on CT and is self-limited. 1, 2
• Bowel obstruction is identified by dilated proximal bowel loops; fever and leukocytosis suggest complicated obstruction with ischemia. 1
• Fecal impaction can cause significant left-sided pain, particularly in elderly or immobile patients. 2
• Perforated colon cancer is the most dangerous diagnosis to miss—look for pericolonic lymphadenopathy >1 cm on CT, which distinguishes it from diverticulitis. 1

Genitourinary Causes

• Pyelonephritis shows perinephric fat stranding on CT. 1
• Nephrolithiasis/renal colic presents with hydronephrosis or visible calculi on imaging. 1
• Urinary tract infection may cause referred pain to the left lower quadrant. 3

Gynecologic Causes (Premenopausal Women)

• Ovarian torsion, ruptured ovarian cyst, tubo-ovarian abscess, and ectopic pregnancy must be excluded with β-hCG testing and pelvic/transvaginal ultrasound before ordering CT. 1, 4
• Cyclical pain in women suggests gynecologic etiology requiring pelvic ultrasound. 4

Rare but Critical Causes

• Appendicitis with redundant cecum or situs inversus can present with left lower quadrant pain—CT immediately reveals the diagnosis. 5, 6, 7
• Spontaneous retroperitoneal or rectus sheath hemorrhage appears on CT as acute bleeding. 8
• Incarcerated hernia requires urgent surgical evaluation. 7
• Psoas abscess may present with left-sided pain and fever. 7

Mandatory Diagnostic Approach

Immediate Imaging

• Order CT abdomen and pelvis with IV contrast immediately for any adult with new left lower quadrant pain—this is rated 8/9 (usually appropriate) by the American College of Radiology and achieves 98% diagnostic accuracy. 1, 2
• Do not rely on clinical examination alone—the classic triad of left lower quadrant pain, fever, and leukocytosis occurs in only 25% of diverticulitis cases, leading to 34-68% misdiagnosis rates. 1
• Obtain β-hCG in all women of reproductive age before CT to avoid fetal radiation exposure. 1

Special Population Modifications

• For premenopausal women with suspected gynecologic pathology, order pelvic/transvaginal ultrasound first. 1, 4
• In pregnant patients, use ultrasound and MRI instead of CT. 1
• For patients with known diverticulosis and mild, intermittent pain without fever or peritoneal signs, imaging may not be necessary—conservative outpatient management is appropriate. 1

Critical Red Flags Requiring Emergency Evaluation

• Fever combined with left lower quadrant pain and elevated WBC suggests complicated diverticulitis or perforation. 1, 2
• Peritoneal signs (guarding, rebound tenderness, rigidity, absent bowel sounds) indicate possible perforation requiring immediate CT and surgical consultation. 1
• Inability to pass gas or stool with abdominal distension suggests bowel obstruction. 1
• Bloody stools, vomiting, or signs of shock mandate emergency department evaluation. 1, 4
• Toxic appearance (rapid breathing, tachycardia, confusion, septic shock) requires immediate intervention. 1

Key CT Findings That Determine Cause

• Pericolonic lymphadenopathy >1 cm → suspect colon cancer, not diverticulitis. 1
• Intestinal wall thickening with pericolonic fat stranding → diverticulitis. 1
• Extraluminal gas or free fluid → perforation requiring surgery. 1
• Pericolic fatty mass with hyperattenuated rim → epiploic appendagitis. 1
• Skip lesions or multi-segment thickening → inflammatory bowel disease. 1
• Perinephric stranding or hydronephrosis → pyelonephritis or nephrolithiasis. 1

Common Pitfalls to Avoid

• Do not assume diverticulitis based solely on history of diverticulosis—alternative pathologies, especially colon cancer, must be excluded with CT. 1
• Do not perform routine colonoscopy after CT-confirmed uncomplicated diverticulitis unless age-appropriate screening is due, or CT shows abscess, perforation, fistula, abnormal lymph nodes, or luminal mass. 1
• Do not order plain radiographs as initial imaging—they have low sensitivity and delay definitive diagnosis. 1
• Do not use ultrasound as primary imaging for non-gynecologic left lower quadrant pain—it is operator-dependent and has limited utility in obese patients. 1, 3

When Functional Bowel Disorder Becomes the Diagnosis

• Functional bowel disorders (e.g., irritable bowel syndrome) are diagnosed only after CT and colonoscopy exclude structural pathology. 4
• Pain related to bowel movements or dietary triggers points toward IBS. 4
• Weight loss, anemia, or change in bowel habits warrant repeat colonoscopy despite prior normal study. 4