Article

Urinary tract ultrasound: kidneys and bladder

Urinary tract ultrasound: kidneys, bladder and excretory tract — technique, measurements, hydronephrosis, stones, post-void residual, normal report and limitations.

What it is and when to indicate it

Urinary tract ultrasound assesses the kidneys, the bladder and, when dilated, the excretory tract. It is indicated for flank pain and renal colic, hematuria, recurrent urinary infection, altered renal function, urinary retention and follow-up of known stones and cysts.

This page organizes the protocol in clear language and does not replace the original guidelines (ACR-AIUM-SPR-SRU, AIUM, CBR), supervised training or clinical correlation.

Preparation and technique

• A full bladder improves assessment of the bladder and the ureterovesical junctions
• Curved transducer of 2 to 5 MHz; abdominal preset with harmonic
• Kidneys assessed supine and in lateral decubitus, using the liver and spleen as a window and deep inspiration
• Each kidney documented in longitudinal and transverse planes, with measurement and parenchymal thickness
• Bladder in two planes; post-void residual when there is a complaint of incomplete emptying

Kidneys: what to measure and assess

• Renal length usually between 9 and 12 cm, with symmetry between sides
• Parenchymal thickness and echogenicity, with good corticomedullary differentiation
• Echogenic renal sinus, without pelvicalyceal dilation
• Simple cysts: anechoic, thin walls, posterior acoustic enhancement (Bosniak I)
• Stones: echogenic foci with acoustic shadowing; assess the twinkling artifact on Doppler

Hydronephrosis and obstruction

Pelvicalyceal dilation is graded and should be correlated with the clinical picture and the possible obstructive factor.

• Mild: dilation of the pelvis and calyces, with preserved parenchyma
• Moderate: rounded calyces and a more dilated pelvis
• Marked: important dilation with parenchymal thinning
• Look for the level and cause (stone, compression, full bladder) and note when not identified
• The ureter is usually only seen when dilated

Bladder and post-void residual

• Thin, regular walls, anechoic content when full
• Wall thickening, trabeculation, stones and vegetating lesions described when present
• Post-void residual estimated by volume (approximately 0.52 x three diameters)
• Ureteral jets on Doppler help confirm the patency of the junctions
• An empty bladder limits the assessment — note it in the report

Normal report template

• Kidneys in topical position, of preserved dimensions and parenchymal thickness, with good corticomedullary differentiation
• No pelvicalyceal dilation and no stones with acoustic shadowing
• Bladder with thin walls and anechoic content, with good emptying
• No significant post-void residual
• No collections or lymphadenopathy in the accessible assessment

Limitations and pitfalls

• Empty bladder hampering bladder and distal ureteral assessment
• Very full bladder simulating mild bilateral dilation (reassess after voiding)
• Parapelvic cyst mistaken for mild hydronephrosis: use planes and Doppler
• Small stone without shadowing: look for the twinkling artifact on Doppler
• Body habitus/gas limiting the assessment — report honestly

Do not overdiagnose

Describe well what is seen, classify cysts by objective criteria, avoid definitive labels on doubtful images, and recommend further workup (new exam with an adequate bladder, non-contrast CT for lithiasis) when clinically relevant.

Sources

Educational content; it does not replace original guidelines, medical evaluation or supervised training. Main references:

• ACR-AIUM-SPR-SRU. Practice Parameter for the Performance of an Ultrasound Examination of the Abdomen and/or Retroperitoneum.
• AIUM. Practice Parameter for the Performance of an Ultrasound Examination of the Kidneys and Urinary Bladder.
• Brazilian College of Radiology (CBR). Standardization and technical guidelines for ultrasound.
• Rumack CM, Levine D. Diagnostic Ultrasound (kidney and bladder).
• Radiopaedia. Renal and bladder ultrasound (didactic support, not copied).

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