Objective: Evaluate for hydronephrosis

Indications: Concern for obstructive renal disease

Anatomy:

The kidney is made up of 4 sonographically distinct areas:

Renal parenchyma:

Renal cortex: Outermost part of kidney parenchyma- homogenous, with low echogenicity compared to liver/spleen (darker). Surrounded by the echogenic capsule (gerota’s fascia)

Renal medulla: Deep to the renal cortex, appears even less echogenic than cortex. Contains renal pyramids which appear as anechoic cone shaped regions

Collecting system:

Renal Calyces: part of the collecting system, contains urine and as such appear anechoic. Not easily visible in the absence of hydronephrosis

Renal pelvis: Central portion of the kidney, site of convergence of calyces. Also contains vasculature. Appears more echogenic (brighter)

 

By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

 

The Renal Exam

Probe selection:

The probe of choice is the phased array probe as it has lower frequency and can penetrate deeply while being able to utilize intercostal windows. Alternatively, one can also use a curvilinear probe if available.

Exam components:

In order to complete an adequate examination:

  1.  Image the left and right kidneys completely in both longitudinal and transverse views.
  2. You can also choose to image the urinary bladder to estimate volume and evaluate for ureteral jets.

Positioning:

  

Place the patient supine or lateral decubitus position. Scanning will take place almost identically to RUQ and LUQ views in the FAST exam

The views:

Right Renal:

  1. Orient the probe in the longitudinal plane with the indicator facing towards the patient’s head.

  2. Choose an area between the 8-11 intercostal space in the mid axillary line to begin scanning.

  3. Likely you will first encounter the liver, once visualized, search for the kidney by fanning posteriorly or sliding caudally until the kidney comes into view

  4. Rotate the probe slightly to obtain a view of the kidney in its longest axis

  5. Fan anterior to posterior to obtain a complete longitudinal view, making sure to to visualize the entire kidney in this plane

  6. With the kidney in view, turn the probe 90 degrees to obtain a image in transverse section.

  7. Fan cephalad to caudal to obtain transverse views of the entire kidney.

 

Image/Image

 

Left renal:

  1. Orient the probe in the longitudinal plane, indicator facing towards patient’s head, in the 5-9th intercostal space, posterior axillary line.

  2. If difficulty in obtaining an image, begin by sliding the probe posteriorly, such that the sonographer’s knuckles are touching the bed. Then angle the probe such that the probe head is pointing anteriorly, with the probe at approximately 20°-30° angle to to bed

  3. Look to orient yourself by finding either spleen or the line of the diaphragm

  4. Once spleen is visualized, fan posteriorly to visualize the kidney

  5. Rotate the probe slightly to obtain a view of the kidney in its longest axis

  6. Be sure to fan through the entire organ in the anterior/posterior dimension

  7. With the kidney in view, turn the probe 90 degrees to obtain a image in transverse section.

  8. Fan cephalad to caudal to obtain transverse views of the entire kidney.

 

Image/Image

Bladder:

  1. Orient the probe in the midsagittal plane, just superior to the pubic symphysis with the probe indicator facing towards the patients head.

  2. Fan in the right to left directions in search of the urinary bladder, which will appear as a cystic structure in the pelvis. If unable to visualize the bladder, adjust the probe in the cephalad/caudal direction until it comes into view.

  3. Once the bladder is in view, adjust the angle of the probe to ensure the entire length of bladder is in view. Fan left to right to visualize the entire width of the bladder

  4. Rotate the probe 90°, counterclockwise, now oriented such that the indicator is facing to the patients right

  5. Fan the probe inferior to superior, making sure to visualize the entire bladder.

  6. Obtain measurements if desired to estimate volume of bladder (will need width and depth on transverse view, length on longitudinal view)

  7. Search for ureteral jets by finding the level of the trigone (image) and using color doppler. Use the seminal vesicles or mid-cervix as an approximate landmark for appropriate level.

 

Image/Image

Image/Image

Image interpretation

 

Grades of Hydronephrosis:

 

Mild

Dilation of renal pelvis +/- dilation of calyces

Renal parenchyma appears normal

 

Moderate

Dilation of renal pelvis and calyces with blunting at papillae

Signs of cortical thinning

Severe

Dilation of renal pelvis/calyces with loss of pelvicalyceal borders (appear ballooned)

Renal cortical atrophy with severe thinning of cortex

 

Pattie’s Pearls

-If you are having difficulty in obtaining adequate views, you can try to place the patient in the lateral decubitus position.

-Hydronephrosis can sometimes be hard to distinguish from vasculature in the renal pelvis: always try placing color doppler on this area to distinguish the two. If there is pulsatile flow, it's vasculature!

-Make sure not to confuse renal pyramids or cysts with hydronephrosis. Renal pyramids will not communicate with the pelvis. Renal cysts will appear circular and have a defined wall

-If looking for ureteral jets, you will need to be patient. They can take several minutes to appear. Presence is reassuring for lack of complete obstructive disease, but absence is not diagnostic.


Written by: Aalap Shah, MD

Peer Reviewed by:

All images obtained by:

 


 

Color Doppler sonography of ureteral jets in normal volunteers: importance of the relative specific gravity of urine in the ureter and bladder.

S M Baker and W D Middleton

American Journal of Roentgenology 1992 159:4, 773-775

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2. Keays MA, Guerra LA, Mihill J et-al. Reliability assessment of Society for Fetal Urology ultrasound grading system for hydronephrosis. J. Urol. 2008;180 (4): 1680-2. doi:10.1016/j.juro.2008.03.107 

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