Children’s Kidney and Urinary Tract Congenital Anomalies

Cause

Transient hydronephrosis

Physiologic hydronephrosis

UPJS

VUR

Megaureter (obstructed and nonobstructed)

MCDK

Ureterocele

Renal cysts

Ectopic ureter

Prune belly syndrome

Urethral atresia

Urachus cysts

Extrarenal causes

Ovarian cyst

Hydrocolpos

Sacrococcygeal teratoma

Gut duplication

Duodenal atresia

Meningocele

UPJS ureteropelvic junction stenosis, VUR vesicoureteral reflux, MCDK multicystic dysplastic kidney

Most authors use anteroposterior diameter (APD) of the renal pelvis for diagnostic classification purposes [1, 2]. In obstetric ultrasound (US), pelvis APD is normally considered pathologic when >4 mm on axial scan during the second trimester and/or >7 mm during the third trimester (in agreement with the results of Corteville et al. reported in the early 1990s and subsequently confirmed) [3].

Dilatation can be further classified according to Grignon et al. [4] into V degrees, associating pyelectasis and calycectasis or, as summarized in the meta-analysis by Lee et al., into mild to moderate to severe (Table 9.2) [5].

Table 9.2

Classification of dilatation of renal excretory system according to Grignon et al. and according to Lee et al.

Grignon et al.	APD (mm)	Lee et al.
Grade I	<10	Hydronephrosis	APD (mm)
Grade II	10–15		Second trimester	Third trimester
Grade III	>15 mild calycectasis	Mild	≤7	≤9
Grade IV	>15 moderate calycectasis	Moderate	7–10	9–15
Grade V	>15 severe calycectasis	Severe	≥10	≥15

Congenital uropathies, in which the etiopathological role of genetic factors is today generally recognized, cause 10–20 % of cases of chronic renal failure in pediatric age [6].

Many of these anomalies are included in the acronym CAKUT (congenital anomalies of the kidney and urinary tract) (Table 9.3) [7].

Table 9.3

Nephrourologic diseases that can be classified as CAKUT (congenital anomalies of the kidney and urinary tract)

Aplasia, hypoplasia, and multicystic dysplastic kidney

Ureteropelvic junction stenosis

Ureterovesical junction stenosis

Vesicoureteral reflux

Duplicate collecting system

Ureteral ectopia

Vesicourethral anomalies

Horseshoe kidney

Warning

Terms such as calycectasis, pyelectasis, hydronephrosis, and megaureter should be dropped since they have a functional connotation of obstruction which US morphology scan is not able to show. According to ESPR uroradiology task force 2014, the term “dilatation” of calyces and/or pelvis and/or ureter should be used, with indication of diameters and related calibers.

CAKUT visualized on US images as urinary tract dilatation are the following: ureteropelvic junction stenosis (UPJS), ureterovesical junction stenosis (UVJS), vesicoureteral reflux (VUR), duplicate collecting system, horseshoe kidney associated with dilatation, and urethral anomalies.

9.1 Ureteropelvic Junction Stenosis (UPJS)

Dilatation of the pelvis and/or renal calyces due to anatomic obstruction of ureteropelvic junction, either congenital or due to extrinsic compression (adhesion bands, abnormal vessels) or to functional compression (e.g., ureteral kinking in renal ptosis/ectopia or horseshoe kidney)

UPJS is often bilateral, usually asymmetric, and more frequent on the left side.

9.1.1 US Findings

Dilatation of renal pelvis of different degrees, with rattail appearance at ureteropelvic junction, without evidence of the ureter under the junction

Color Doppler US imaging is important to identify possible abnormal inferior pole vessels that can cross the ureteropelvic junction. In patients with UPJS, this examination must always be associated with classical bidimensional US.

In our hospital, about 21 % of UPJS treated with surgery between 2006 and 2014 were due to vascular compression suspected at US examination and confirmed by MRI.

9.2 Ureterovesical Junction Stenosis (UVJS)

UVJS is defined as primary when characterized by distal ureteral dilatation due to functional obstruction caused by aperistalsis of the terminal ureter and secondary when due to vesical anomalies or urethral obstructions (neurogenic bladder, low-compliance bladder, ureterocele, abnormal ureteral implantation, posterior urethral valves).

9.2.1 US Findings

Dilatation of the whole ureter, sometimes also of pelvis and calyxes, with caudo-cranial decrease.

The lumbar ureter, when markedly dilated, presents typically convoluted, mainly in the newborn and nursling, due to “immaturity.” The pelvic ureter is easily studied using the vesical window both with transverse, longitudinal, and oblique scans. Generally, it is possible to identify the pre- and/or intramural stenotic tract.

9.3 Vesicoureteral Reflux (VUR)

VUR is due to a congenital anomaly of the ureterovesical junction determined by an altered ratio of length to diameter of intramural ureter.

VUR is classified into five grades, from the less severe to the most severe, according to the importance of urinary tract dilatation.

Depending on VUR grade and on the possible presence of parenchymal scars, US findings can range from fully normal kidneys to kidneys with different degrees of urinary tract dilatation and with parenchymal dysmorphisms (thinned poles, stretched and “corticalized” calyces, reduced renal size).

Vesico-ureteral reflux grading by the international classification (degrees I to V from left to right). Fowler JE Jr: Urinary tract infection and inflammation. Chicago, Year Book Medical Editor,1989.

9.3.1 Cystosonography

Investigation of VUR is indicated in case of renal pelvis dilatation associated with ureteral dilatations and/or of recurrent UTI symptoms.

The use of second-generation US contrast media allows the US diagnosis of VUR. In children, the introduction of contrast medium into the bladder for US examination has been proposed for the identification of VUR for radiation protection purposes, even though this use in children is off-label [8–11].

Second-generation US contrast media, characterized by signal intensity no longer related to rupture of microbullae but rather to their excitation, allow the execution of cystosonography with more intense and long-lasting signal and therefore with an improved diagnostic efficacy and anatomic definition.

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