What is the differential diagnosis for left lower quadrant abdominal pain?

Differential Diagnosis for Left Lower Quadrant Pain

Most Common Causes

Acute sigmoid diverticulitis is the leading cause of left lower quadrant pain in adults, particularly those over age 50, with prevalence increasing 50% between 2000-2007. 1, 2

The comprehensive differential diagnosis includes:

Gastrointestinal Causes

• Diverticulitis (sigmoid or descending colon) - most common in adults >50 years 1, 2
• Colitis (infectious, ischemic, inflammatory bowel disease) 1, 2
• Epiploic appendagitis 1, 2
• Bowel obstruction 1, 2
• Fecal impaction 2
• Perforated colon cancer - can mimic diverticulitis clinically and radiographically 1, 3
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis) 1, 2

Genitourinary Causes

• Pyelonephritis 1, 2
• Nephrolithiasis/renal colic 1, 4
• Urinary tract infection 4

Gynecologic Causes (in premenopausal women)

• Ovarian pathology (torsion, cyst rupture, ectopic pregnancy) 1
• Fallopian tube pathology (pelvic inflammatory disease, tubo-ovarian abscess) 1

Other Causes

• Incarcerated hernia 1, 5
• Psoas abscess 5
• Spontaneous retroperitoneal or rectus sheath hemorrhage 6
• Abdominal wall pathology 4
• Appendicitis with atypical presentation (long appendix projecting into LLQ or situs inversus) 7, 5

Critical Distinguishing Features

Key Red Flag: Perforated Cancer vs. Diverticulitis

Pericolonic lymphadenopathy >1 cm in short axis strongly suggests malignancy over diverticulitis and mandates colonoscopy. 3 This is the single most important CT finding to differentiate these conditions, as perforated adenocarcinoma can perfectly mimic diverticulitis in all other respects. 3

Clinical Triad for Diverticulitis

The classic triad of left lower quadrant pain, fever, and leukocytosis is present in only 25% of diverticulitis cases, making clinical diagnosis alone unreliable with misdiagnosis rates of 34-68%. 1, 3

Immediate Diagnostic Approach

CT abdomen and pelvis with IV contrast is the single most important diagnostic test, with 98% diagnostic accuracy, and should be ordered immediately for most patients with left lower quadrant pain. 1, 2 The American College of Radiology rates this as 8/9 (usually appropriate). 1, 2

Special Population Considerations

• For premenopausal women with suspected gynecologic pathology: Order pelvic/transvaginal ultrasound as initial imaging 1
• For women of reproductive age: Obtain beta-hCG testing before CT to avoid radiation exposure to potential fetus 1
• For pregnant patients: Use ultrasonography and MRI instead of CT 1

When Imaging May Not Be Necessary

In patients with known diverticulosis presenting with mild, intermittent left lower quadrant pain without fever, peritoneal signs, or vomiting, conservative outpatient management without imaging is appropriate. 1 However, CT should be obtained if fever, severe/worsening pain, inability to tolerate oral intake, peritoneal signs, or persistent symptoms beyond 2-3 days develop. 1

Critical Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is mandatory for: 1

• Fever with inability to pass gas or stool
• Severe abdominal tenderness with guarding or rebound tenderness
• Vomiting
• Bloody stools
• Signs of shock (hypotension, tachycardia, altered mental status)
• Progressively worsening pain over several days
• Free air on imaging indicating perforation

Common Pitfalls to Avoid

• Do not rely on clinical examination alone - misdiagnosis rates are 34-68% without imaging 1, 3
• Do not miss colon cancer - always look for pericolonic lymphadenopathy >1 cm on CT as the key differentiator from diverticulitis 3
• Do not forget rare presentations - appendicitis can present with LLQ pain if the appendix is unusually long or in cases of situs inversus 7, 5
• Do not assume diverticulitis is the only diagnosis - CT identifies alternative diagnoses in approximately 49% of patients with non-localized pain 1