What are the causes of left abdominal pain?

Causes of Left Abdominal Pain

Acute diverticulitis of the sigmoid or descending colon is the most common cause of left lower quadrant pain in adults, accounting for the majority of cases, though colitis, inflammatory bowel disease, epiploic appendagitis, bowel obstruction, hernia, ovarian/fallopian tube pathology, pyelonephritis, and urolithiasis must all be considered in the differential diagnosis. 1

Primary Gastrointestinal Causes

Most Common: Diverticular Disease

• Acute colonic diverticulitis represents the leading etiology, with a 50% increase in incidence between 2000 and 2007 1
• Approximately 10% of Western populations have diverticulosis at age 40, increasing to 70% or more in older patients 1
• Between 5-25% of patients with diverticulosis will develop diverticulitis 1
• Results from inflammation of colonic diverticula, commonly linked to inadequate dietary fiber in Western populations 1

Other Gastrointestinal Etiologies

• Colitis (infectious, ischemic, or inflammatory) presents with overlapping symptoms to diverticulitis 1
• Inflammatory bowel disease (Crohn's disease or ulcerative colitis) can manifest with left-sided pain 1
• Epiploic appendagitis (inflammation of colonic fat appendages) mimics diverticulitis clinically 1
• Bowel obstruction from various causes including adhesions, malignancy, or volvulus 1
• Perforated colon cancer can present similarly to complicated diverticulitis 2

Urologic Causes

• Pyelonephritis (kidney infection) causes flank pain radiating to the left lower quadrant 1
• Urolithiasis (kidney stones) with sensitivity and specificity near 100% on unenhanced CT 1
• Urinary tract infection may present with lower abdominal pain 2

Gynecologic Causes (in Women)

• Ovarian pathology including cysts, torsion, or masses 1
• Fallopian tube pathology such as ectopic pregnancy or pelvic inflammatory disease 1
• Endometriosis can cause cyclical left lower quadrant pain 3
• Pelvic/transvaginal ultrasound is the preferred initial imaging for premenopausal women with suspected gynecologic pathology 3

Abdominal Wall Causes

• Hernia (inguinal, femoral, or incisional) can present with localized left lower quadrant pain 1
• Abdominal wall pathology including muscle strain or hematoma 2

Functional Disorders

• Irritable bowel syndrome becomes the most likely diagnosis when structural pathology has been excluded by CT and colonoscopy 4
• Pain typically colicky in nature, most commonly on the left side, with bloating that worsens throughout the day 5
• Pain and bowel dysfunction often exacerbated by eating 5

Critical Diagnostic Approach

Red Flag Symptoms Requiring Emergency Evaluation

• Fever with inability to pass gas or stool suggests complicated diverticulitis or obstruction 3
• Severe abdominal tenderness with guarding indicates possible perforation with peritonitis 3
• Vomiting, bloody stools, or signs of shock mandate immediate assessment 3
• Progressively worsening pain over several days requires urgent evaluation 3

Imaging Strategy

• CT abdomen and pelvis with IV contrast is the preferred imaging modality with 98% diagnostic accuracy, rated 8/9 (usually appropriate) by the American College of Radiology 3
• CT with IV contrast detects complications (abscess, fistula, obstruction, perforation), identifies alternative diagnoses, and guides treatment decisions 3
• Unenhanced CT is acceptable when IV contrast is contraindicated, though less accurate for detecting abscesses (rated 6/9) 3
• Ultrasound with graded compression can reduce unnecessary CT examinations but is operator-dependent and limited in obese patients 3

Important Pitfalls to Avoid

• Clinical diagnosis alone is unreliable with misdiagnosis rates between 34-68% 3
• The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases 3
• Pericolonic lymphadenopathy >1 cm on CT suggests malignancy rather than diverticulitis and requires colonoscopy 3, 4
• Weight loss, anemia, or change in bowel habits warrant colonoscopy despite prior normal imaging 4