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ULTRASOUND
AbdomenDemonstration data

Renal Ultrasound

Renal ultrasound is the first-line imaging test for evaluating the kidneys and urinary bladder without ionizing radiation or contrast. It reliably detects hydronephrosis, renal size and parenchymal changes, cysts, masses, and calculi, and is essential in the workup of renal failure and hematuria. Doppler adds assessment of renal and, in transplants, vascular perfusion.

Indications

  • Acute or chronic kidney injury to assess size, echogenicity, and obstruction
  • Suspected hydronephrosis or urinary tract obstruction
  • Hematuria evaluation and detection of renal or bladder masses
  • Nephrolithiasis and follow-up of known stones
  • Characterization of a renal mass or cyst
  • Renal transplant assessment of perfusion, collecting system, and perinephric collections
  • Suspected renovascular disease or renal artery stenosis with Doppler
  • Guidance for renal biopsy or nephrostomy

Contraindications & Cautions

  • No absolute contraindications; radiation-free and contrast-free
  • Limited sensitivity for small or mid-ureteric stones compared with CT
  • Body habitus and bowel gas limit visualization, especially of the ureters
  • Non-distended bladder limits assessment of bladder wall and distal ureters
  • Follow ALARA principles for Doppler thermal exposure

Patient Preparation

  • No strict fasting required; a moderately full bladder aids bladder and distal ureter evaluation
  • Explain the examination; no consent needed for diagnostic scanning
  • Positioning supine, decubitus, and prone as needed; transplant kidneys imaged over the iliac fossa
  • Deep inspiration to bring kidneys below the ribs
  • Document relevant history including creatinine, hematuria, and prior stones

Technique & Parameters

  • Curvilinear 2-5 MHz transducer; higher frequency for thin patients and transplants
  • Both kidneys imaged in longitudinal and transverse planes with maximal bipolar length measured (normal 9-12 cm)
  • Assess cortical thickness, echogenicity relative to liver and spleen, and corticomedullary differentiation
  • Evaluate collecting system for hydronephrosis, grading mild to severe
  • Scan for calculi with attention to echogenic foci, posterior shadowing, and twinkle artifact
  • Bladder assessed for volume, wall thickness, masses, and ureteric jets with color Doppler
  • Doppler assessment of main renal arteries and intrarenal arteries with resistive index (normal <0.70)
  • Transplant protocol adds evaluation of anastomoses, resistive indices, and perinephric collections

Systematic Review

  • Kidney size and bipolar length bilaterally
  • Cortical thickness and echogenicity versus adjacent liver or spleen
  • Corticomedullary differentiation and pyramids
  • Collecting system for dilation and grade of hydronephrosis
  • Renal calculi with size, location, and shadowing
  • Focal renal lesions: cystic versus solid characterization
  • Bladder volume, wall, masses, and ureteric jets
  • Doppler: arterial waveforms, resistive index, venous patency (especially transplants)

Key Findings & Significance

  • Small echogenic kidneys with thinned cortex indicate chronic kidney disease
  • Increased cortical echogenicity with preserved size suggests medical renal disease
  • Dilated calyces and renal pelvis indicate hydronephrosis; degree grades severity
  • Echogenic focus with posterior shadowing and twinkle artifact confirms a calculus
  • Anechoic thin-walled lesion with posterior enhancement is a simple (Bosniak I) cyst
  • Complex cyst with septa, calcification, or a solid enhancing component raises malignancy concern
  • Elevated resistive index (>0.80) in a transplant suggests rejection, ATN, or obstruction

Differential Considerations

  • Bilateral small echogenic kidneys: chronic glomerulonephritis, hypertensive nephrosclerosis, diabetic nephropathy
  • Unilateral enlarged kidney: obstruction, pyelonephritis, renal vein thrombosis, infiltrative tumor
  • Cystic renal lesion: simple cyst, complex cyst, ADPKD, cystic RCC, multilocular cystic nephroma
  • Solid renal mass: renal cell carcinoma, angiomyolipoma (echogenic), oncocytoma, lymphoma, metastasis
  • Hydronephrosis: obstructing stone, UPJ obstruction, tumor, extrinsic compression, reflux, pregnancy
  • Transplant dysfunction: ATN, rejection, obstruction, renal artery stenosis, collection

Pearls & Pitfalls

  • Pelvicalyceal dilation is not always obstruction; extrarenal pelvis, reflux, and a full bladder can mimic hydronephrosis
  • Twinkle artifact on color Doppler improves detection of small calculi
  • An echogenic renal lesion is most often an angiomyolipoma but a small RCC can also be echogenic; consider CT/MRI
  • Parapelvic cysts can mimic hydronephrosis; they do not communicate and lack a connecting infundibulum
  • Measure resistive indices in transplant kidneys at upper, mid, and lower poles
  • Column of Bertin and dromedary hump are normal variants that can simulate a mass
  • Assess the bladder before it is emptied to capture ureteric jets and wall pathology

Structured Report

  • Report bilateral kidney sizes, cortical thickness, and echogenicity
  • Describe hydronephrosis presence and grade, and identify obstructing lesion if seen
  • Characterize renal lesions with size, cystic versus solid, and Bosniak category where applicable
  • Report bladder findings and Doppler resistive indices, especially in transplants
  • State technical limitations
  • Impression: concise summary highlighting obstruction, masses requiring CT/MRI, or transplant complications with recommendations

References

  • ACR-AIUM-SRU Practice Parameter for the Performance of an Ultrasound Examination of the Kidneys and Urinary Bladder
  • Bosniak Classification of Cystic Renal Masses, version 2019
  • ACR Appropriateness Criteria: Renal Failure and Hematuria
  • Rumack CM, Levine D. Diagnostic Ultrasound, 5th edition

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.