Ultrasonography of hydronephrosis
Choice of modality
- Ultrasonography of hydronephrosis is generally the first initial choice.
- CT of kidney stone disease in older patients with flank pain and hematuria.
Several conditions can result in urinary obstruction. In both adults and children, masses, such as abscesses and tumors, can compress the ureter. In children, hydronephrosis can be caused by ureteropelvic junction obstruction, ectopic inserted ureter, primary megaureter and posterior urethral valve (Figure 13). In the latter, both kidneys will be affected. In adults, hydronephrosis can be caused by urolithiasis, obstructing the outlet of the renal pelvis or the ureter, and compression of the ureter from, e.g., pregnancy and retroperitoneal fibrosis. Urolithiasis is the most common cause of hydronephrosis in the adult patient and has a prevalence of 10%–15%.
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).
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).
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.
Figure 15. End-stage hydronephrosis with cortical thinning. Measurement of pelvic dilatation on the US image is illustrated by ‘+’ and a dashed line.
Figure 16. Hydronephrosis with dilated anechoic pelvis and calyces, along with cortical atrophy. The width of a calyx is measured on the US image in the longitudinal scan plane, and illustrated by ‘+’ and a dashed line.
Figure 17. Same patient as in Figure 16 with measurement of the pelvis dilation in the transverse scan plane illustrated on the US image with ‘+’ and a dashed line.
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:
- 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.
- Adults, defineddifferently by different sources, with anteroposterior diameters ranging between 10 and 20 mm. About 13% of normal healthy adults have a transverse pelvic diameter of over 10 mm.
- 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.
- Grade 1 (mild) – Mild renal pelvis dilation (anteroposterior diameter less than 10 mm in fetuses) without dilation of the calyces nor parenchymal atrophy
- Grade 2 (mild) – Moderate renal pelvis dilation (between 10 and 15 mm in fetuses), 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
- For a full list of contributors, see article Radlines:Authorship for details. . Creators of images are attributed at the image description pages, seen by clicking on the images. See
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