2.3 Etiology of Hydronephrosis

Figs. 2.15 and 2.16 Intravenous urography showing bilateral hydroureters and hydronehrosis secondary to exteral compression by a distended vagina and uterus

(hydrometrocolpos) secondary to vaginal atresia. This will resolve once the vaginal atresia is treated

Figs. 2.20 and 2.21 Inra-operative photographs showing hydrometrocolpos secondary to vaginal atresia. The distended vagina and uterus will lead to compression on

the ureters leading to hydroureteronephrosis. Drainage of the hydrometrocolpos will lead to relief of the obstruction and resolution of the hydroureteronephrosis

•The causes of hydronephrosis with or without hydroureter depends on:

–The site of obstruction

–Whether it is unilateral or bilateral

–Whether it is intrinsic, extrinsic or functional.

•The following are the main causes of hydronephrosis in infants and children:

–Pelvi-ureteric junction obstruction

–Ureterovesical junction obstruction

–Ureteral folds and valves

–Benign fibroepithelial polyps

–Retrocaval ureter

–Neurogenic bladder

–Hydrocolpos and hydrometrocolpos

–Bladder exstrophy

–Duplicated renal collecting systems

–Multi cystic dysplastic kidney

–Retroperitoneal lymphoma and sarcoma

–Retroperitoneal fibrosis

–Renal, bladder and ureteric calculi

–Vesicoureteric reflux

–Posterior urethral valve

–Urethral stricture

–Uretrocele

–Posterior urethral valves

–Urethral atresia

–Phimosis and meatal stenosis

•Multi cystic dysplastic kidney (MCDK) (Figs. 2.35, 2.36, and 2.37):

–This will show several round, well defined, cystic structures within the kidney that often look just like severe hydronephrosis.

–These abnormally developed kidneys are generally found early in pregnancy through antenatal ultrasounds.

–The true diagnosis can be confirmed postnatally by the following tests:

•If they develop unmanageable high blood pressure

•If they are complicated by severe infection

•There are several congenital and acquired conditions that can lead to hydronephrosis in infants and children.

•Congenital causes:

–PUJ (Pelvi-Ureteric Junction) obstruction

–Posterior urethral valve

–Uretro-vesical junction (UVJ) obstruction

–Vesicoureteric reflux

–Abnormal polar vessels

–Uretrocele

–Primary megaureter

–Neurogenic bladder

–Severe meatal stenosis

•Acquired causes:

–Kidney and ureteric stones

–Blood clots

–Retroperitoneal fibrosis

–Urethral stricture

–Tumors

•In children and in neonates, the relative frequency of the causes of antenatal hydronephrosis has been determined to be as follows:

–Transient (48 %)

–Physiologic (15 %)

–Ureteropelvic junction obstruction (11 %)

–Vesicoureteral reflux (9 %)

–Megaureter (4 %)

–Multicystic dysplastic kidney (2 %)

–Ureterocele (2 %)

–Posterior urethral valves (1 %)

2.4Classification

of Hydronephrosis (Figs. 2.38, 2.39, 2.40, 2.41, and 2.42)

•The widespread use of antenatal ultrasound revealed a significant structural fetal anomaly in 1 % of pregnancies.

•The probability of detecting these abnormalities depends on the experience and skills of the sonographer.

•The distribution of these anomalies is as follows:

–50 % involve the central nervous system

–20 % are genitourinary

–15 % are gastrointestinal

–8 % are cardiopulmonary

•An abnormality involving the genitourinary tract may be expected in as many as 1 in 100 pregnancies.

•The prevalence of antenatally detected hydronephrosis (ANH) is variable depending on the gestational age, diagnostic criteria and skills of the radiographer and ranges from 0.6% to 5.4%.

•Among the genitourinary anomalies, hydronephrosis is the commonest anomaly detected antenatally.

•The causes and distribution of antenatally diagnosed hydronephrosis are as follows:

–Transient hydronephrosis (40–80 %)

–Multicystic dysplastic kidney (5 %)

–Duplex system (4–6 %)

–Posterior urethral valve (1–2 %)

–Others (Urethral atresia, Prune belly syndrome, etc.)

•There are several systems to grade and classify hydronephrosis.

•Hydronephrosis can be classified depending on the onset into:

–Acute

–Chronic

•Hydronephrosis is also classified depending on the degree of obstruction into:

–Complete

–Partial

•Hydronephrosis is also classified depending on the side into:

–Unilateral

–Bilateral

•Grading of antenatal hydronephrosis based on renal pelvis antero-posterior diameter:

–Mild

•Second trimester (4–6 mm)

•Third trimester (7–9 mm)

–Moderate

•Second trimester (7–10 mm)

•Third trimester (10–15 mm)

–Severe

– Second trimester (>10 mm)

– Third trimester (>15 mm)

•The most common system used (Society of Fetal Ultrasound, SFU) was originally designed for grading neonatal and infant hydronephrosis:

–Grade 0:

•No dilatation, calyceal walls are opposed to each other

–Grade 1 (mild):

•Dilatation of the renal pelvis without dilatation of the calyces

•No parenchymal atrophy

–Grade 2 (mild):

•Dilatation of the renal pelvis (mild) and calyces (pelvicalyceal pattern is retained)

•No parenchymal atrophy

–Grade 3 (moderate):

•Moderate dilatation of the renal pelvis and calyces

•Blunting of fornicies and flattening of papillae

•Mild cortical thinning may be seen

–Grade 4 (severe):

•Gross dilatation of the renal pelvis and calyces, which appear ballooned

•Loss of borders between the renal pelvis and calyces

•Renal atrophy seen as cortical thinning