- 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):
- 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
- Select probe
- Curvilinear/large convex probe (phased array probe may substitute)
- 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
- Right kidney
- Scan entire kidney (through liver)
- Longitudinal (long axis) and transverse (short axis) views
- Scan the bladder
- Mild: Distention of collecting system
- Moderate: Dilation of collecting system, rounding of calyces
- Severe: Dilated renal calyces and cortical thinning
- “Bear claw” appearance
- Represents severe obstructive uropathy
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.
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.
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.
- Smith-Bindman R, Aubin C, Bailitz J, et al. Ultrasonography versus computed tomography for suspected nephrolithiasis. NEJM. 2014; 371(12):1100–1110.
- Cosby, K. (2006) Practical Guide to Emergency Ultrasound. Philadelphia, PA: Lippincott Williams & Wilkins pp. 237, 245-248