Acute Abdomen Imaging

Initial Imaging Approach - First Look Wins

Patient stability is paramount. Imaging choice: clinical suspicion, patient factors (age, pregnancy), ALARA principle, and local resources.

• Patient Stability:
  • Unstable: Bedside X-ray (chest, abdomen supine/erect) & FAST scan.
  • Stable: Proceed with specific, targeted imaging.
• Key Modalities:
  • X-ray: Initial screen for bowel obstruction, free air (perforation), radiopaque foreign bodies.
  • Ultrasound (USG): Preferred for RUQ (gallbladder), RLQ (appendix in children/females, GYN), AAA, renal colic. Radiation-free.
  • CT Scan: Often definitive; high sensitivity/specificity. IV contrast typically used.

⭐ Erect chest X-ray detects free air (>1mL) from perforation; CT is far more sensitive.

X-ray & USG Roles - Classic Clues Unveiled

• X-ray (Plain Films):
  • Uses: Pneumoperitoneum, bowel obstruction/ileus, radiopaque foreign bodies.
  • Signs:
    • Free air under diaphragm (perforation).
    • Dilated bowel (SB >3cm, LB >6cm, Cecum >9cm), air-fluid levels (obstruction).
    • 📌 Sigmoid volvulus: Coffee bean sign.
• Ultrasound (USG):
  • Uses: Appendicitis, cholecystitis, intussusception, AAA, renal colic, Gynae emergencies.
  • Signs:
    • Appendicitis: Non-compressible appendix >6mm diameter, target sign.
    • Cholecystitis: GB wall >3mm, sonographic Murphy's, stones, pericholecystic fluid.
    • Intussusception: Target/doughnut sign.

CT Abdomen/Pelvis - Detective's Sharp Eye

• Workhorse for acute abdomen; IV contrast standard. Oral/rectal contrast selective.
• Phases: Non-contrast (stones), Arterial (bleed/vascular), Portal Venous (standard), Delayed (collections/urography).

Key CT Findings:

⭐ Pneumatosis intestinalis and/or portal venous gas are ominous signs in mesenteric ischemia, suggesting infarction.

Special Populations & Pitfalls - Tricky Patient Cases

• Pregnant Patients:
  • US first-line (appendicitis, cholecystitis, renal colic).
  • MRI for equivocal appendicitis (non-ionizing). Avoid CT.
• Pediatric Patients:
  • US primary (appendicitis, intussusception - target sign).
  • Malrotation/Volvulus: UGI series (corkscrew), US (whirlpool).
• Elderly/Immunocompromised:
  • Atypical presentations common. ↑Risk of ischemia, atypical infections (e.g., typhlitis).
  • Low threshold for comprehensive CT.
• Pitfalls:
  • Appendicitis mimics: Meckel's diverticulitis, ovarian torsion, Crohn's disease.
  • Right-sided diverticulitis vs. appendicitis.
  • ⭐

    Epiploic appendagitis: CT shows characteristic ovoid fatty lesion with hyperattenuating rim & central dot; crucial to recognize as self-limiting.

High‑Yield Points - ⚡ Biggest Takeaways

• Erect X-ray Abdomen detects pneumoperitoneum (gas under diaphragm) and intestinal obstruction (air-fluid levels).
• Ultrasound (USG) is primary for acute cholecystitis, appendicitis (children/pregnant), and gynecological emergencies.
• CECT is IOC for pancreatitis, diverticulitis, bowel ischemia, trauma, and abscesses.
• Rigler's sign (bowel wall air on both sides) indicates pneumoperitoneum.
• Target sign suggests intussusception; Whirlpool sign indicates volvulus or torsion.
• NCCT KUB is preferred for renal colic.