Renal and Urinary Tract Imaging

Imaging Modalities & Normal Anatomy - Toolkit Tour

• Key Structures: Kidneys (cortex, medulla, pelvicalyceal system; 9-13 cm length), ureters (constrictions: PUJ, pelvic brim, VUJ), bladder, urethra. Visualized variably by modality.

⭐ Non-contrast CT (NCCT) KUB is the gold standard for suspected renal/ureteric colic.

Urolithiasis & Obstruction - Stone Patrol

• NCCT KUB: Gold standard for stone detection (all types).
• USG KUB: Initial, pregnancy, children; detects hydronephrosis, renal stones.
  • Twinkling artifact on color Doppler.
• X-ray KUB: Only radiopaque stones (Calcium, Struvite).
• Stone Types:
  • Calcium Oxalate (most common, opaque).
  • Struvite (infection, staghorn, opaque).
  • Uric Acid (lucent on X-ray, visible on CT/USG). 📌 Radiolucent: Uric acid, Xanthine, Indinavir.
  • Cystine (faintly opaque/lucent).
• Obstruction Signs: Hydronephrosis (Grades I-IV), perinephric stranding on CT.
• Intervention: Often for stones >5-7 mm.

⭐ Twinkling artifact on color Doppler USG is highly suggestive of small renal calculi, even when not clearly visible on B-mode imaging.

Renal Masses & Cysts - Lump Busters

• Renal Cell Carcinoma (RCC): Most common renal malignancy.
  • Subtypes: Clear Cell (most common), Papillary, Chromophobe.
  • CT: Solid, enhancing mass (>15-20 HU ↑). Necrosis, calcification.
• Angiomyolipoma (AML): Benign; fat, smooth muscle, vessels.
  • CT: Fat (HU < -10).
  • Bleed risk if > 4 cm.
• Oncocytoma: Benign; central scar (non-specific).
• Transitional Cell Carcinoma (TCC): Urothelial origin; filling defect in collecting system.

Bosniak Classification of Renal Cysts

Approach to Renal Mass

Renal Infections & Trauma - Crisis Crew

• Acute Pyelonephritis (APN):

  • USG: Often normal; ↑renal size, ↓CMD.
  • CECT (Gold Std): Wedge-shaped ↓enhancement, perinephric stranding.

• Complications:

  • Renal Abscess: CECT: liquefaction, ring enhancement.
  • Emphysematous Pyelonephritis (EPN): Gas in kidney. CECT for staging (Type 1 vs 2).

    ⭐ Emphysematous pyelonephritis, characterized by gas in the renal parenchyma/collecting system, is a life-threatening infection often seen in diabetics.

  • Pyonephrosis: Pus in obstructed system. USG: debris/levels.
  • XGPN: Chronic; staghorn (Proteus). "Bear paw sign" (CECT).

• Renal Trauma:

  • CECT: Modality of choice.
  • AAST Renal Injury Scale:

    Grade	Description
    I	Contusion/subcapsular hematoma, non-expanding.
    II	Laceration < 1 cm cortex, no urine extravasation.
    III	Laceration > 1 cm cortex, no urine extravasation.
    IV	Laceration to collecting system; segmental vascular injury.
    V	Shattered kidney; main renal artery/vein injury.

High‑Yield Points - ⚡ Biggest Takeaways

• IVU is gold standard for papillary necrosis & medullary sponge kidney.
• USG is initial choice for hydronephrosis, renal masses & calculi in pregnancy.
• CT Urography excels in hematuria evaluation, complex cysts & RCC staging.
• Doppler USG is key for renal artery stenosis & renal vein thrombosis.
• MCU for VUR & PUV; RGU for anterior urethral strictures.
• Wilms' tumor shows "claw sign", indicating intrarenal origin_