Radiographic Anatomy of Abdomen

Abdominal X-rays - The Inside Story

• Key Projections & Purpose:
  • Supine (AP): Standard initial view; gas pattern, calcifications, soft tissues.
  • Erect AP: Detects free intraperitoneal air (under diaphragms), air-fluid levels.
  • Left Lateral Decubitus: Alternative to erect for free air (over liver).
• Common Clinical Indications:
  • Suspected bowel obstruction or perforation.
  • Renal/ureteric colic (KUB for calculi).
  • Ingested foreign bodies.
• Normal Intestinal Gas:
  • Stomach: Air bubble in fundus.
  • Small Bowel: Minimal, central; diameter <2.5 cm.
  • Large Bowel: Peripheral, feces/gas; haustra.

⭐ Plain abdominal X-ray is often the first imaging modality for suspected bowel obstruction or perforation.

Organ Spotting - Shadows & Shapes

• Liver: RUQ, largest solid organ shadow; inferior angle often visible.
• Spleen: LUQ, ovoid shadow; posterior to stomach, often obscured by gas.
• Kidneys: Retroperitoneal, bean-shaped; typically T12-L3. Right often slightly lower. Outlines visible due to perinephric fat.
• Psoas Margins: Triangular, extend inferomedially from transverse processes of lumbar vertebrae. Clearly defined by fat.

  ⭐ Loss of the psoas muscle outline can indicate retroperitoneal pathology like abscess, hematoma, or tumor.

• Properitoneal Fat Stripe: Thin radiolucent line lateral to ascending/descending colon.
• Gas Patterns (Normal):
  • Stomach: LUQ, variable air-fluid level.
  • Small Bowel: Central, few loops, feathery (valvulae conniventes).
  • Large Bowel: Peripheral, sacculated (haustra), contains gas/faeces.

Trouble Bubbles - Air Apparent

• Pneumoperitoneum: Free air (perforation).
• Key Signs:
  • Rigler's sign 📌 (bowel wall visible)
  • Cupola sign (subphrenic air)
  • Football sign (massive)
• Best View: Erect CXR, L. Lat. Decubitus.

Stone Cold Evidence - Calcifications & Co.

• Renal Calcifications:
  • Nephrocalcinosis (medullary/cortical).
  • Renal calculi:
    • Radio-opaque: Calcium oxalate/phosphate (most common).
    • Radiolucent: Uric acid, xanthine.

  ⭐ Staghorn calculi are typically composed of struvite (magnesium ammonium phosphate) and are associated with recurrent UTIs by urease-producing bacteria.

• Biliary System:
  • Gallstones: ~10-20% radio-opaque on X-ray.
  • Porcelain gallbladder: Calcified wall, ↑ malignancy risk.
• Pancreatic Calcifications:
  • Pathognomonic for chronic pancreatitis; scattered throughout gland.
• Vascular Calcifications:
  • Atherosclerosis: Linear/tram-track (e.g., aorta, iliacs).
  • Phleboliths: Common pelvic calcifications, often with lucent centers.
• Miscellaneous:
  • Appendicolith, adrenal (TB, old bleed), LN (TB, histo), fibroid (popcorn).

High‑Yield Points - ⚡ Biggest Takeaways

• Diaphragm domes separate chest and abdomen; clear costophrenic angles are crucial.
• Liver occupies the RUQ; its inferior edge is a vital plain film landmark.
• Spleen resides in the LUQ, often obscured by gastric or colonic gas.
• Kidneys are retroperitoneal; perinephric fat aids their visualization; right kidney is typically lower.
• Clear Psoas muscle outlines are important indicators of retroperitoneal integrity.
• Bowel gas patterns (stomach, small/large bowel) are key to identifying obstruction or ileus.
• Note properitoneal fat lines and their displacement in abdominal pathology.