Abdominal Ultrasonography

USG Basics & Artifacts - Pixel Puzzles

• Physics: Piezoelectric effect (PZT). ↑Frequency = ↑Resolution, ↓Penetration. Impedance mismatch → reflection.
• Modes: B-mode (2D), M-mode (motion), Doppler (Color/Spectral for flow).
• Echogenicity: Anechoic (fluid, black) 📌 All Fluid Black, Hypoechoic (dark), Hyperechoic (calcification/bone, white).
• Common Artifacts:
  • Acoustic Shadowing: Post. to stones/bone.
  • Acoustic Enhancement: Post. to cysts/fluid.
  • Reverberation: Parallel lines (comet tail).
  • Mirror Image: Mirror across reflector (diaphragm).
  • Twinkle: Color Doppler, stones.

⭐ Posterior acoustic enhancement helps differentiate cystic vs. solid lesions.

Liver & Biliary USG - Bile Buddies 📌

• Liver Findings:
  • Normal: Homogeneous, < 15.5 cm. Portal Vein < 13 mm.
  • Fatty Liver (Steatosis): ↑Echogenicity (liver > R. kidney), vascular blurring.
  • Cirrhosis: Coarse texture, nodular surface, caudate hypertrophy, ascites.
  • Focal Lesions:
    • Cyst: Anechoic, posterior acoustic enhancement.
    • Hemangioma: Uniformly hyperechoic (most common benign).
    • HCC: Variable echogenicity, halo, Doppler flow.
• Gallbladder & Biliary Tree Findings:
  • Normal GB & CBD: GB wall < 3 mm. CBD < 7 mm (↑ 1mm/decade >60y; up to 10mm post-cholecystectomy).
  • Cholelithiasis: Mobile hyperechoic foci + posterior acoustic shadowing.
  • Acute Cholecystitis: GB wall > 3 mm, pericholecystic fluid, +ve Sonographic Murphy's sign.
  • Chronic Cholecystitis: Thick wall, WES sign (Wall-Echo-Shadow).
  • Biliary Dilatation: Intrahepatic (parallel channel/"too many tubes"), Extrahepatic.

    ⭐ Sonographic Murphy's sign (focal tenderness over GB with transducer pressure) is highly specific for acute cholecystitis.

Pancreas & Spleen Scan - Belly Besties

• Pancreas:
  • Normal: Homogeneous, echogenicity ≥ liver. Pancreatic duct < 3mm. Splenic vein posterior.
  • Acute Pancreatitis: Enlarged, hypoechoic, peripancreatic fluid.
  • Chronic Pancreatitis: Atrophic, calcifications, ductal dilatation.
  • Masses: Adenocarcinoma (hypoechoic, often in head).
• Spleen:
  • Normal: Homogeneous, echotexture like liver. Length < 12-13 cm.
  • Splenomegaly: > 13 cm (causes: portal HTN, infections).
  • Focal Lesions: Cysts (anechoic), infarcts (wedge-shaped, hypoechoic).

⭐ Accessory spleen (splenunculus): common variant near hilum/pancreatic tail; don't mistake for pathology.

Renal & Retroperitoneal USG - Kidney Chronicles

• Normal Kidney: Length 9-13 cm. Cortex typically hypoechoic or isoechoic to liver/spleen. Medullary pyramids more hypoechoic. Central sinus fat is hyperechoic.
• Hydronephrosis: Dilation of pelvicalyceal system. Graded I-IV. Identify level & cause (e.g., stone, stricture, mass).
• Renal Calculi: Hyperechoic foci with posterior acoustic shadowing. 📌 Twinkling artifact on color Doppler is a key sign.
• Renal Cysts: Simple cysts: anechoic, thin smooth walls, posterior acoustic enhancement. Complex cysts: septations, wall thickening, calcifications, internal echoes.
• Renal Cell Carcinoma (RCC): Typically solid, variable echogenicity (often isoechoic/hyperechoic), may show internal vascularity on Doppler.
• Retroperitoneum: Scan for collections (hematoma, abscess), lymphadenopathy. Evaluate major vessels like aorta & IVC.

⭐ Angiomyolipomas (AMLs) are common benign renal tumors, typically markedly hyperechoic due to high fat content.

FAST & GI Tract Hints - Gut Feelings & Trauma Triage

• FAST: Rapid trauma scan for free fluid (hemoperitoneum, pericardial effusion).
  • 4 Key Views: Morrison's, perisplenic, pelvic, subxiphoid.
  • eFAST: Adds lung views (pneumothorax).
• GI Tract US:
  • Appendicitis: Diameter >6mm, non-compressible, target sign.
  • Intussusception: Target/doughnut sign. 📌 "Sausage Loves Doughnuts".
  • Pyloric Stenosis: Muscle >3mm thick, canal >15mm long.

⭐ Key US criteria for hypertrophic pyloric stenosis: pyloric muscle thickness >3mm and length >15mm.

High‑Yield Points - ⚡ Biggest Takeaways

• First-line imaging for acute abdomen, especially cholecystitis, appendicitis (children/pregnant), and hydronephrosis.
• Gallstones: hyperechoic foci with posterior acoustic shadowing; cholecystitis: wall thickening >3mm, sonographic Murphy's.
• Liver: cirrhosis (coarse echotexture), fatty liver (↑echogenicity), focal lesions.
• Kidneys: hydronephrosis, stones (echogenic + shadowing), cysts.
• FAST scan detects free fluid/hemoperitoneum in trauma.
• Appendicitis: non-compressible tube >6mm, target sign.
• AAA: abdominal aorta >3cm.