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Ultrasonographic Anatomy

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Ultrasound Basics - Echoes & Shadows

  • Echogenicity: Describes tissue's ability to reflect ultrasound waves.
    • Anechoic (black): No echoes (e.g., fluid-filled cysts, blood vessels).
    • Hypoechoic (dark grey): Few echoes (e.g., muscle, some tumors).
    • Isoechoic: Same as surrounding tissue.
    • Hyperechoic (bright white): Many echoes (e.g., bone, gallstones, fat, air).
  • Key Acoustic Artifacts:
    • Acoustic Shadowing: ↓ signal posterior to strong reflectors (e.g., stones, bone).

      ⭐ Acoustic shadowing is classically seen posterior to gallstones or calcifications.

    • Acoustic Enhancement: ↑ signal posterior to fluid-filled structures (e.g., cysts, bladder).
    • Reverberation: Multiple parallel echoes (e.g., comet tail with gas).
    • Edge Shadowing: Refractive shadow at curved edges. Ultrasound acoustic enhancement diagram

Abdominal Ultrasonography - Viscera Views

  • Liver: Homogeneous; echogenicity > renal cortex.
    • Segments: Couinaud.
    • Views: Subcostal, intercostal.
    • Signs: 📌 Portal triad (Mickey Mouse), 📌 Hepatic veins (Playboy bunny).
  • Gallbladder & Biliary Tree:
    • GB wall: <3 mm.
    • CBD: Normal <6 mm (↑ 1 mm/decade >60 yrs; up to 10 mm post-cholecystectomy).
  • Spleen: Homogeneous; echogenicity > liver. Length <12-13 cm.
  • Pancreas: Echogenicity > liver (↑ with age/fat). Landmark: Splenic vein posteriorly.
  • Kidneys: Cortex hypoechoic to liver/spleen. Medulla more hypoechoic than cortex. Sinus fat hyperechoic. Length 9-12 cm.
  • Aorta/IVC:
    • Aorta: Pulsatile, non-compressible, diameter <3 cm.
    • IVC: Compressible, respiratory variation.

⭐ The seagull sign on ultrasound refers to the celiac artery and its branches (splenic and common hepatic arteries).

Pelvic & Small Parts Ultrasonography - Beyond Belly

  • Pelvic USG: Assesses uterus, ovaries, adnexa, bladder, prostate.
    • Approaches: Transabdominal (TAS) overview; Transvaginal (TVS) detail (female); Transrectal (TRUS) prostate.
    • Uterus: Endometrial thickness (postmenopausal <5mm no HRT). Myometrium.
    • Ovaries: Follicles, cysts, masses. Ovarian volume assessment.
    • Prostate (TRUS): Volume, peripheral zone (commonest Ca site).

    ⭐ The "sliding sign" in pelvic ultrasound is important for assessing adhesions, particularly in endometriosis.

  • Small Parts USG: High-frequency linear probes for superficial structures.
    • Thyroid: Isthmus AP diameter <5mm. Nodules (TIRADS), thyroiditis.
    • Scrotum: Testicular torsion, epididymo-orchitis, varicocele (vein diameter >2-3mm with Valsalva), hydrocele.
    • MSK: Tendinopathy, tears, effusions, dynamic assessment.
    • Other: Eye (globe, lens), Neck LNs (morphology). Male Pelvic Anatomy Diagram

Doppler Ultrasound & FAST - Flow & Trauma

  • Doppler Ultrasound: Assesses blood flow using Doppler effect.

    • Detects direction & velocity. 📌 BART: Blue Away, Red Towards.
    • Applications: DVT, stenosis, perfusion, fetal heart.
    • Types:
      • Color Doppler: Visualizes flow.
      • Power Doppler: ↑ sensitivity for low flow, no direction.
      • Spectral Doppler: Waveform analysis (RI, PI).
        • RI = $(PSV - EDV) / PSV$
        • PI = $(PSV - EDV) / TAMV$
  • FAST (Focused Assessment with Sonography for Trauma): Rapidly detects free fluid (e.g., hemoperitoneum) in trauma.

    • Key in ATLS. 📌 4 Ps (Views):
      • Perihepatic (Morrison's Pouch)
      • Perisplenic
      • Pelvic
      • Pericardial (Subxiphoid)
    • eFAST: Adds lung views (pneumo/hemothorax).

    ⭐ In trauma, the most common site for initial free fluid accumulation in the supine patient is Morrison's pouch (hepatorenal space).

FAST Exam: Right Upper Quadrant View

High‑Yield Points - ⚡ Biggest Takeaways

  • Acoustic impedance mismatch is the basis of ultrasound imaging.
  • Structures: hyperechoic (bright, e.g., bone), hypoechoic (darker, e.g., muscle), anechoic (black, e.g., simple cyst).
  • Doppler ultrasound assesses blood flow direction and velocity.
  • FAST scan rapidly detects free fluid (hemoperitoneum, pericardial effusion) in trauma.
  • Transducer choice: high-frequency for superficial (high resolution), low-frequency for deep (good penetration).
  • Common artifacts: acoustic shadowing (e.g., gallstones) and posterior acoustic enhancement (e.g., cysts).

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Practice Questions: Ultrasonographic Anatomy

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Which of the following is best assessed by FAST USG?

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Flashcards: Ultrasonographic Anatomy

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In the mid-clavicular line, the inferior border of lung is at the _____ rib and for pleura is at the level of 8th rib

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