Left Iliac Fossa (LIF) Pain — Differentials

1. Gastrointestinal (Most Common)

Sigmoid Diverticulitis ⭐ (Commonest cause in adults >40)

• Classic triad: LIF pain + fever + leukocytosis
• May radiate to left loin; pneumaturia/fecaluria if colovesical fistula forms
• Complications: pericolic abscess (30%), fistula (14%), free perforation (1–2%), bowel obstruction
• CT abdomen/pelvis with contrast is the diagnostic gold standard
• Differential from colorectal cancer is important — Textbook of Family Medicine notes the differential includes IBD, colon cancer, ischemic colitis, and bowel obstruction
• Current Surgical Therapy 14e — sigmoid colon; Gray's Anatomy for Students

Inflammatory Bowel Disease (IBD)

• Crohn's disease: can affect sigmoid/descending colon; cramping, diarrhea, weight loss
• Ulcerative colitis: left-sided colitis or proctosigmoiditis; bloody diarrhea, tenesmus

Irritable Bowel Syndrome (IBS)

• Chronic, relapsing; pain typically relieved by defecation; altered bowel habit
• No systemic features (afebrile, normal bloods)

Constipation

• Very common; hard stool palpable in the left colon
• Especially in elderly/opiate users

Colorectal Carcinoma (Sigmoid/Descending Colon)

• Change in bowel habit, rectal bleeding, weight loss, iron deficiency anaemia
• Mass may be palpable; obstruction can cause acute LIF pain

Bowel Obstruction

• Large bowel: distension, absolute constipation, vomiting (late)
• Often due to tumour, stricture, or volvulus

Sigmoid Volvulus

• Acute-onset abdominal distension + pain; more common in elderly/institutionalised
• Characteristic "coffee bean" sign on plain AXR

Ischaemic Colitis

• Typically older patients with vascular risk factors; bloody diarrhea + LIF pain

Epiploic Appendagitis

• Self-limiting inflammation of fat appendages of sigmoid colon
• Acute, localised, constant pain; no systemic upset; CT diagnostic

Mesenteric Lymphadenitis

• More common in children/young adults; often post-viral; diffuse lower abdominal pain

2. Urological

Ureteric Colic (Left Ureter)

• Severe, colicky, loin-to-groin radiation; haematuria
• Patient unable to lie still (differentiates from peritonitis)

Urinary Tract Infection / Pyelonephritis

• Dysuria, frequency, systemic features; left loin/LIF tenderness

Left Renal/Ureteric Calculus

• As above with colicky pain

3. Gynaecological (Females)

Rosen's Emergency Medicine emphasises: ectopic pregnancy, haemorrhagic ovarian cyst, and ovarian torsion are highly morbid conditions that must be excluded urgently in females with acute LIF pain.

4. Musculoskeletal

• Psoas abscess: fever, pain on hip extension (positive psoas sign); often from Crohn's disease, TB, or vertebral osteomyelitis
• Inguinal/femoral hernia: groin swelling ± obstruction; strangulation causes acute pain
• Iliacus haematoma: typically in anticoagulated patients; painful hip flexion
• Rectus sheath haematoma: lateral to midline; follows cough/trauma

5. Vascular

• Aortic aneurysm (leaking AAA): severe tearing pain; pulsatile mass; haemodynamic shock — immediate emergency
• Mesenteric ischaemia: pain out of proportion to examination; often in AF/vascular disease patients

6. Rare / Miscellaneous

• Situs inversus — appendicitis presenting in LIF (rare but reported)
• Left-sided appendix (malrotation)
• Meckel's diverticulum (younger patients)
• Retroperitoneal lymphadenopathy (lymphoma)
• Transplanted kidney (LIF) — allograft pyelonephritis

Key Approach Summary