Ultrasonography of hydronephrosis

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Authors: Mikael Häggström; Authors of Creative Commons article[1] [notes 1]


Choice of modality


Hydronephrosis is seen as an anechoic fluid-filled interconnected space within the renal sinus.[1] If it is not interconnected, consider parapelvic renal cysts. Normally, the dilated pelvis can be differentiated from the dilated calyces.[1]

Look at both kidneys as well as the urinary bladder.

Figure 13. Hydronephrosis due to ureteropelvic junction obstruction in a pediatric patient.[1]

Hydronephrosis grading

Society for Fetal Urology (SFU) grading of hydronephrosis.jpg

The Society of Fetal Ultrasound has developed a grading system for hydronephrosis, initially intended for use in neonatal and infant hydronephrosis, but it is now used for grading hydronephrosis in adults as well:[3]

  • Grade 0 – No renal pelvis dilation. Cutoff values for different patient populations are:
  • Fetuses: An anteroposterior diameter of less than 4 mm in fetuses up to 32 weeks of gestational age and 7 mm afterwards.[4]
  • Adults, defineddifferently by different sources, with anteroposterior diameters ranging between 10 and 20 mm.[5] About 13% of normal healthy adults have a transverse pelvic diameter of over 10 mm.[6]
  • Pregnant women in the last two trimesters: The maximum normal expected renal pelvic diameter (97.5 percent prediction interval) is 27 mm on the right and 18 mm on the left.[7]
  • Grade 1 (mild) – Mild renal pelvis dilation (anteroposterior diameter less than 10 mm in fetuses[4]) without dilation of the calyces nor parenchymal atrophy
  • Grade 2 (mild) – Moderate renal pelvis dilation (between 10 and 15 mm in fetuses[4]), including a few calyces
  • Grade 3 (moderate) – Renal pelvis dilation with all calyces uniformly dilated. Normal renal parenchyma
  • Grade 4 (severe) – As grade 3 but with thinning of the renal parenchyma

In Swedish practice,[notes 2] the most important is a subjective classification into mild, moderate or severe, with optional mention of numerical grade (unless specifically requested in the referral).


Look particularly at the most distal end of dilation of the renal pelvis or ureter for a possible cause, including:

Ultrasound of the urinary bladder, showing the "keyhole sign" indicating lower urinary tract obstruction. The main "hole" corresponds to a distended urinary bladder (white arrow) and the slit (black arrow) is a distended proximal urethra.

In case of hydronephrosis of both kidneys, look at the bladder since it may indicate a lower urinary tract obstruction.

Figure 14. Bilateral dilatation of the ureters due to vesicoureteric reflux in a pediatric patient.[1]

Under normal conditions, the ureter is not seen with US. However, in, e.g., urinary obstruction and vesicoureteric reflux with dilation of the ureter, the proximal part in continuation with the renal pelvis, as well as the distal part near the ostium can be evaluated (Figure 14).[1]

The hydronephrosis is typically graded visually and can be divided into five categories going from a slight expansion of the renal pelvis to end-stage hydronephrosis with cortical thinning (Figure 15). The evaluation of hydronephrosis can also include measures of calyces at the level of the neck in the longitudinal scan plane, of the dilated renal pelvis in the transverse scan plane and the cortical thickness, as explained previously (Figure 16 and Figure 17).[1]

If the fluid in the dilated collecting system has echoes, pyonephrosis should be excluded by clinical exam, blood analysis and, in special cases, puncture or drainage. Hydronephrosis can also be caused by non-obstructive conditions, such as brisk diuresis in patients treated with diuretics, in pregnant women and in children with vesicoureteral reflux.[1]


  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.
  2. NU Hospital Group, Sweden


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 Content initially copied from: Hansen, Kristoffer; Nielsen, Michael; Ewertsen, Caroline (2015). "Ultrasonography of the Kidney: A Pictorial Review ". Diagnostics 6 (1): 2. doi:10.3390/diagnostics6010002. ISSN 2075-4418.  (CC-BY 4.0)
  2. Brisbane, Wayne; Bailey, Michael R.; Sorensen, Mathew D. (2016). "An overview of kidney stone imaging techniques ". Nature Reviews Urology 13 (11): 654–662. doi:10.1038/nrurol.2016.154. ISSN 1759-4812. 
  3. Laurence S Baskin. Overview of fetal hydronephrosis. Version Version 29.0. UpToDate. Retrieved on 2017-04-25. Last updated Apr 20, 2017
  4. 4.0 4.1 4.2 Page 189 in: V. D'Addario (2014). Donald School Basic Textbook of Ultrasound in Obstetrics & Gynecology . JP Medical Ltd. ISBN 9789351523376. 
  5. Page 78 in: Justin Bowra, Russell E (2011). Emergency Ultrasound Made Easy, Edition 2 . Elsevier Health Sciences. ISBN 9780702048722. 
  6. "Sonographic evaluation of renal appearance in 665 adult volunteers. Correlation with age and obesity ". Acta Radiol 34 (5): 482–5. 1993. doi:10.3109/02841859309175388. PMID 8369185. 
  7. Erickson, L. M.; Nicholson, S. F.; Lewall, D. B.; Frischke, Lauraline (1979). "Ultrasound evaluation of hydronephrosis of pregnancy ". Journal of Clinical Ultrasound 7 (2): 128–132. doi:10.1002/jcu.1870070211. ISSN 00912751.