Renal ultrasound

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Background

  • Bedside renal ultrasound has accepted use in the diagnosis of nephrolithiasis
  • In comparison of diagnosis by CT vs. U/S (by EP) vs. U/S (by radiologist):[1]
    • No difference in rate of missed high-risk diagnoses that resulted in complications (pyelo/sepsis/diverticular abscess)
    • No difference in rate of serious adverse events, pain scores, return emergency department visits, or hospitalizations

Indications

Technique

  1. Select probe
    • Curvilinear/large convex probe (phased array probe may substitute)
  2. Location
    • Right kidney
      • Patient supine
      • Probe in the right lower intercostal space in the midaxillary line
    • Left kidney
      • Patient supine or right lateral decubitus
      • Probe in the lower intercostal space on the posterior axillary line
      • More cephalad and posterior than when visualizing the right kidney
  3. Scan entire kidney (through liver)
    • Longitudinal (long axis) and transverse (short axis) views
  4. Scan the bladder

Findings

Hydro.png

  • Hydronephrosis
    • Mild: Distention of collecting system
    • Moderate: Dilation of collecting system, rounding of calyces
    • Severe: Dilated renal calyces and cortical thinning[2]
      • “Bear claw” appearance
      • Represents severe obstructive uropathy

Images

Normal

Abnormal


Pearls and Pitfalls

  • Patients that are overhydrated, pregnant, or with a full-bladder may have mild hydronephrosis bilaterally without obstruction
  • Underhydrated patients may not have hydronephrosis on initial renal scanning, despite obstruction
  • Renal cysts can sometimes be mistaken for hydronephrosis
    • Cysts are typically single, circular, and arise in the periphery of the kidney
    • They can be multiple as in polycystic kidney disease

Renal Cyst Classification

  • Bosniak I :Benign simple cyst with thin wall without septa, calcifications, or solid components.
  • Bosniak II: Benign cyst with a few thin septa, which may contain fine calcifications or a small segment of mildly thickened calcification. Hyperdense cysts must be exophytic with at least 75% of its wall outside the kidney to allow for appropriate assessment of margins, otherwise they are categorized as IIF.
    • Bosniak IIF: Includes renal cysts with multiple thin septa, a septum thicker than hairline, slightly thick wall, or with calcification, which may be thick. It also includes intrarenal cysts larger than 3 centimetres (1.2 inches). Category IIF cysts have a 5-10% risk of being kidney cancer, and therefore follow-up is recommended every 6 months.
  • Bosniak III: Indeterminate cystic masses with thickened irregular septa with enhancement. 50 % of these lesions are ultimately found to be malignant.
  • Bosniak IV: Malignant cystic masses with all the characteristics of category III lesions but also with enhancing soft tissue components on CT independent of but adjacent to the septa. 100 %of these lesions are malignant.

Documentation

Normal Exam

A bedside ultrasound was conducted to assess for hydronephrosis with clinical indication of left/right flank pain. The left kidney, right kidney, and bladder were identified in the transverse and sagittal plane. There was no hydronephrosis identified.

Abnormal Exam

A bedside ultrasound was conducted to assess for hydronephrosis with clinical indication of left/right flank pain. The left kidney, right kidney, and bladder were identified in the transverse and sagittal plane. There was mild/moderate/severe hydronephrosis identified on the left/right.

Clips

Normal

Abnormal

Pitfall

External Links

See Also

References

  1. Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. NEJM. 2014; 371(12):1100–1110.
  2. Cosby, K. (2006) Practical Guide to Emergency Ultrasound. Philadelphia, PA: Lippincott Williams & Wilkins pp. 237, 245-248

Authors

Neil Young