Renal and Urinary Tract Imaging

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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.
ModalityFocusPro(s)Con(s)
X-ray KUBCalcification, gasBasic, cheapLow detail
USGHydronephrosis, cysts, renal stonesNo radiation, real-timeOperator-dependent, gas
IVUUrothelial detail, functionFunctional, anatomyContrast risk, radiation
CT (NCCT/CECT)Stones (NCCT), masses, trauma (CECT)Gold standard (stones), detailRadiation, contrast (CECT)
MRISoft tissue, problem-solvingNo X-ray, superior contrast resCost, time, limited availability
Nuclear ScansRenal function (GFR), drainageQuantitative functionPoor anatomy

⭐ 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.

NCCT KUB: Renal calculi measurement

⭐ 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

CategoryDescriptionMalignancy RiskManagement
ISimple cyst, thin wall, no septa/calcification~0%Ignore
IIFew thin septa, fine calcification~0%Ignore
IIFMore septa, minimal smooth wall thickening~5%Follow-up
IIIThick/irregular septa/wall, measurable enhancement~50%Surgery/Biopsy
IVSolid enhancing components~100%Surgery

Approach to Renal Mass

CT scan of Bosniak IV renal cyst

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:
      GradeDescription
      IContusion/subcapsular hematoma, non-expanding.
      IILaceration < 1 cm cortex, no urine extravasation.
      IIILaceration > 1 cm cortex, no urine extravasation.
      IVLaceration to collecting system; segmental vascular injury.
      VShattered 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_

Practice Questions: Renal and Urinary Tract Imaging

Test your understanding with these related questions

In acute pyelonephritis, which of the following is NOT a USG finding:

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Flashcards: Renal and Urinary Tract Imaging

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Investigation of choice in renal cell carcinoma to evaluate IVC and renal vein involvement is _____.

TAP TO REVEAL ANSWER

Investigation of choice in renal cell carcinoma to evaluate IVC and renal vein involvement is _____.

MRI

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