Click on the button below to go to the main page:

Click on the button below to go to the previous page:

HYDRONEPHROSIS

Important Concepts:

1. Absence of hydronephrosis does not exclude an obstructing calculus

2. Severe hydronephrosis is more likely to be associated with a large stone or chronic obstruction

3. Conditions other than renal calculi can cause hydronephrosis

Bedside US for renal colic decreases cost, ED length of stay and radiation to the patient (1,2). Bedside US has moderate sensitivity for detecting hydronephrosis. However, the sensitivity improves with increased stone size >6mm (3) and focussed training (4,5).

Some of the features of obstructing renal calculi on US is the presence of unilateral hydronephrosis, a stone seen within the collecting system and/or decreased ureteric jets (6). 

Stones are visualised with US in the first third of the ureter or at the VUJ. The intervening ureter is typically obscured by bowel gas.

Hydronephrosis may not be present with partial obstruction and small stone size, patient dehydration and acute onset of pain (2). Stones >5mm are more likely to cause moderate to severe hydroneprhosis (7). Conversely patients without hydronephrosis are much less likely to have stones requiring surgical intervention. Infusing 500ml of saline may improve the diagnosis of hydronephrosis on bedside US (8); however, studies have shown subjects without pathology may develop bilateral mild hydronephrosis after fluid infusion. 

POCUS hydronephrosis US vs CT: Bourcier JE, Gallard E, Redonnet JP, Abillard M, Billaut Q, Fauque L, Jouanolou A, Garnier D. Ultrasound at the patient's bedside for the diagnosis and prognostication of a renal colic. Ultrasound J. 2021 Nov 22;13(1):45

GRADES OF HYDRONEPHROSIS

Grading of hydronephrosis is visual (9)

Grade 1

- pelvic and ureteric dilatation only

Grade 2

- above + some calyceal dilatation

Grade 3

- above + all calyces dilated

Grade 4

- above + thin cortex

STONE

A renal calculus on US is hyperechoic with or without a posterior shadow. Stones without shadowing are more likely to be <5mm in size (10). Stone size on US is notoriously misleading (11). Colour doppler on the stone gives rise to a typical twinke artefact (12).

pelvis long: stone at VUJ

twinkle artefact

URETERIC JETS

An obstructing stone may cause decreased or absent ureteric jets due to obstruction. Absent ureteric jets are more likely with a high grade obstruction (13). Patience is need to visualise the jets. The key is to have the tranducer in transverse with the probe marker to the patient's right and fan anteriorly to visualise the bladder trigone. Have the colour doppler nyquist limit low (5-10) and increase the colour gain until just below the speckle artefact. Then hold your hand still until you visualise jets bilaterally.

pelvis trans: normal ureteric jet from the left ureter, there was no jet on the right due to obstructing calculus

PERINEPHRIC FREE FLUID 

Presence of perinephric fluid usually indicates calyceal fornix rupture (14). These patients usually go on to further imaging with CT, however, most are managed conservatively. Presence of perinephric fluid is associated with increased pain (15).

Like retroperitoneal free fluid seen on EFAST, perinephric fluid is seen as an anechoic rim around the kidney deep to the hyperechoic Gerota's fascia.

DDx FOR HYDRONEPHROSIS 

Nephrolithiasis is the most common cause of hydronephrosis. However, there are many intrinsic and extrinsic causes of hydronephrosis which you should consider. For example, pregnancy, malignancy, AAA, abdominal masses, congenital causes, bladder outlet obstruction etc.

WHEN TO CT 

The STONE score is a validated score which predicts the likelihood renal colic is the cause of the patient's presentation (16). Using this, patients <50yo with typical pain which is quickly settled with analgesia, usually do not need a CT. The following list is some of the features you should consider before relying on US alone to make the diagnosis of renal colic. As always, US is best as a rule in test. If in doubt progress to further imaging or involve the urology team.  

HIGH RISK FEATURES

Past Hx:

Single kidney

Renal transplant

Clinical:

- Age >50yo

- Anterior abdominal mass or tenderness

- Fever

- UTI on urinalysis

- First presentation or atypical presentation

- unrelenting pain

- representation

Ultrasound

- grade 3-4 hydronephrosis

- large stone with posterior acoustic shadowing

- absent ureteric jet

- perinephric fluid

Biochemical

- renal impairment

Click on the button below to go to the next page:

REFERENCES

1. Blecher G, Meek R, Egerton-Warburton D, McCahy P. Introduction of a new imaging guideline for suspected renal colic in the ED reduces CT urography utilisation. Emerg Med J. 2017 Nov;34(11):749-754.

2. Dalziel PJ, Noble VE. Bedside ultrasound and the assessment of renal colic: a review. Emerg Med J. 2013 Jan;30(1):3-8.

3. Riddell J, Case A, Wopat R, Beckham S, Lucas M, McClung CD, Swadron S. Sensitivity of emergency bedside ultrasound to detect hydronephrosis in patients with computed tomography-proven stones. West J Emerg Med. 2014 Feb;15(1):96-100.

4. Bourcier JE, Gallard E, Redonnet JP, Abillard M, Billaut Q, Fauque L, Jouanolou A, Garnier D. Ultrasound at the patient's bedside for the diagnosis and prognostication of a renal colic. Ultrasound J. 2021 Nov 22;13(1):45

5. Herbst MK, Rosenberg G, Daniels B, Gross CP, Singh D, Molinaro AM, Luty S, Moore CL. Effect of provider experience on clinician-performed ultrasonography for hydronephrosis in patients with suspected renal colic. Ann Emerg Med. 2014 Sep;64(3):269-76.

6. Nicolau C, Claudon M, Derchi LE, Adam EJ, Nielsen MB, Mostbeck G, Owens CM, Nyhsen C, Yarmenitis S. Imaging patients with renal colic-consider ultrasound first. Insights Imaging. 2015 Aug;6(4):441-7.

7. Goertz JK, Lotterman S. Can the degree of hydronephrosis on ultrasound predict kidney stone size? Am J Emerg Med. 2010 Sep;28(7):813-6.

8. Henderson SO, Hoffner RJ, Aragona JL, Groth DE, Esekogwu VI, Chan D. Bedside emergency department ultrasonography plus radiography of the kidneys, ureters, and bladder vs intravenous pyelography in the evaluation of suspected ureteral colic. Acad Emerg Med. 1998 Jul;5(7):666-71.

9. Kim SY, Kim MJ, Yoon CS, Lee MS, Han KH, Lee MJ. Comparison of the reliability of two hydronephrosis grading systems:The Society for Foetal Urology grading system vs. the Onen grading system. Clin Radiol. 2013;68(9):e484–e490.

10. May PC, Haider Y, Dunmire B, Cunitz BW, Thiel J, Liu Z, Bruce M, Bailey MR, Sorensen MD, Harper JD. Stone-Mode Ultrasound for Determining Renal Stone Size. J Endourol. 2016 Sep;30(9):958-62.

11. Ray AA, Ghiculete D, Pace KT, Honey RJ. Limitations to ultrasound in the detection and measurement of urinary tract calculi. Urology. 2010 Aug;76(2):295-300.

12. Nabheerong P, Kengkla K, Saokaew S, Naravejsakul K. Diagnostic accuracy of Doppler twinkling artifact for identifying urolithiasis: a systematic review and meta-analysis. J Ultrasound. 2023 Jun;26(2):321-331.

13. Burge HJ, Middleton WD, McClennan BL, Hildebolt CF. Ureteral jets in healthy subjects and in patients with unilateral ureteral calculi: comparison with color Doppler US. Radiology. 1991 Aug;180(2):437-42

14. Thom C, Eisenstat M, Moak J. Point-of-Care Ultrasound Identifies Urinoma Complicating Simple Renal Colic: A Case Series and Literature Review. J Emerg Med. 2018 Jul;55(1):96-100.

15. Nadav G, Eyal K, Noam T, Yeruham K. Evaluation of the clinical significance of sonographic perinephric fluid in patients with renal colic. Am J Emerg Med. 2019 Oct;37(10):1823-1828

16. Moore CL, Bomann S, Daniels B, Luty S, Molinaro A, Singh D, Gross CP. Derivation and validation of a clinical prediction rule for uncomplicated ureteral stone—the STONE score: retrospective and prospective observational cohort studies. BMJ. 2014;348:g2191.