Fetal and Postnatal Hydronephrosis: Etiology, Update on New Classification and Management - HD

Introduction

Hello, my name's Man Deke from University of Washington in Seattle and my lecture topic today is fetal and postnatal urinary tract dilatation.

Objectives

My objectives for this lecture today are to cover the normal anatomy of the fetal urinary system and its appearance on ultrasound and MRI, the postnatal anatomy of the urinary system and the appearance of on different modalities.

I'll talk a little about etiology and some cases of antenatal hydronephrosis and some of their postnatal correlation.

We will then discuss the description of new urinary tract dilatation classification, which is called as a UTD classification and in the management and follow-up options in antenatal and postnatal TD.

Antenatal Ultrasound Anatomy

In terms of antenatal ultrasound anatomy, the kidneys are seen at about 10 to 12 weeks but by transvaginal ultrasound only.

This picture here shows the kidneys in this fetus bilaterally and on a sagittal or a coronal reformatted image from a 3D image.

Again, you can see the kidneys on both sides, normal grams for the renal length, width and thickness as well as volume exist.

But in clinical practice we don't actually use normal grams.

We just use an approximate rule of renal length is equal to fetal age in weeks.

So in this image you can see an ultrasound image in a sagittal orientation showing the left kidney and it measures 32 millimeters in a fetus who is 32 weeks in gestational age.

As if a a gestation progresses.

The kidneys are seen as bilateral hypoechoic round structures on either side of the fetal spine and in third trimesters you can actually see the medullary pyramids and cortex as separate entities as seen.

In this case, the ureters are not usually visible unless they're dilated when they're seen as these tubular linear fluid filled avascular structures.

The bladder is seen as a round anti coic fluid filled structure in the pelvis with the umbilical arteries seen on either side of the bladder.

Antenatal MRI Anatomy

In terms of MRI, the signal intensity on T two weighted images A DC values and renal cortex and medulla ra, the ratio increases with gestational age and reaches maximum at tone.

Both kidneys are seen bilaterally in this T two weighted coronal image with the renal pelvis seen as a fluid filled structure, the bladder is seen as a fluid filled structure in the pelvis.

Antenatal Hydronephrosis

Now antenatal hydronephrosis is one of the commonest abnormalities seen on prenatal ultrasound.

It is seen in one to 5% of pregnancies.

It can be transient or physiologic and has no clinical significance.

The definition of a NH is variable and clinical management is not systematically defined.

Hence the diagnosis of a NH can cause significant parental anxiety and physician uncertainty.

When it comes to pre and postnatal management, commonly the an posterior diameter of the renal pelvis is measured on the transverse plane.

There are some disadvantages and limitations of this A PD.

Only one measurement of the collecting system dilatation can be measured, may not accurately reflect the degree of HID nephrosis.

There are no formal studies to determine the inter intra observer reproducibility of the A PD measurement and it does not consider glacial dilatation or parenchymal changes such as increased echogenicity or parenchymal thinning that may reflect most severe cases of obstruction.

These are the normal references for renal pelvises published in various studies and you can see that they're all over the place right from two to three millimeters to 15 millimeters.

Grading Systems for Antenatal Hydronephrosis

A grading system has been described with the traditional grading system is more descriptive with mild, moderate and C severe forms.

This is very subjective and does not have good inter observer reliability.

Other terms that can be used for hydronephrosis are pelvic cases, pelvic calc cases and calc cases which describe the different degrees of hydronephrosis.

Anterior posterior renal pelvic diameter has been described as a quantitative method and is preferred by the maternal fetal medicine specialist.

This table shows the degrees of an antenatal hydronephrosis as calibrated by A PRD and these are mild moderate C.

They can, the mild in second trimester varies from four to seven millimeters.

In third trimester seven to nine millimeters, moderate is seven to 10 millimeters and third trimester nine to 15 millimeters and CVO in second trimester would be greater than 10 millimeters in third trimester greater than 15 millimeters.

The society of fetal urology has a semi-quantitative method of quantifying antenatal hydro necrosis.

This is preferred by the pediatricians.

It goes from grade zero to grade four, which is a CMOs form and as you can see, there's increasing degree of dilatation with no dilatation seen in grade zero dilatation of the renal pelvis without dilation of the caly seen in grade one, which is mild hydrosis dilation of the renal pelvis which is mild and caly in grade two, which is again quantified as mild subjectively moderate dilatation of the renal pelvis and caly which may have blunting of the foris and flattening of the pape with maybe mild cortical thinning as moderate hydronephrosis or grade three and grade four, which is the C severe form is gross rotation of the renal pelvis and caly which appear ballooned.

There's loss of borders between the renal pelvis and caly and cortical atrophy as well.

The European Society of Pediatric Radiology and Neuroradiology task force came up with their own classification which extends from HN or hydronephrosis zero to HN five and has increasing degrees of hydronephrosis as illustrated in this particular picture.

Onin in his paper came up with a grading system as well, which is Exte, uh, from grade one to grade four again with increasing degrees of hydronephrosis.

As shown in this graphical picture,

Other Sonographic Parameters

There are other sonographic parameters that are to be evaluated as well.

For example, poor cortico medi medullary differentiation which is lack of ultrasound, visualization of the renal pyramids increased echogenicity as seen in this particular patient with hydronephrosis and increased echogenicity of the kidney and the presence of renal cyst.

Presence of perinephric Oma could indicate severe urinary obstruction and rupture of the collecting system.

Sagittal length of the fetal bladder increases in cases with bladder outlet obstruction.

Hydronephrosis index has also been proposed, which is the anti posterior diameter of the renal pelvis divided by the urinary bladder volume by lowering etal oligo oligohydramnios is the most important predictive factor 'cause it can predict the function of the kidneys.

Etiology of Antenatal Hydronephrosis

In terms of etiology of a NH, transient hydronephrosis is the commonest seen in about 41 to 88% of cases.

Next is UPJ obstruction in about 10 to 30% of cases Versico retic reflux in about 10 to 20% of cases and other causes include UVJ obstruction, mega ureters, multicystic, dysplastic kidneys, posterior urethral valves, urethral seals with ectopic ureters or DU collecting system and congenital diseases like prune belly syndrome, cystic kidney disease or reary structures and Melo urethra.

Postnatal Evaluation of Hydronephrosis

In terms of postnatal evaluation of ID nephrosis, this can be divided into two categories.

Morphologic assessment, which includes a detailed anatomical information and can be done with either ultrasound or MRI and functional assessment.

Functional assessment is limited by the transient physiological renal immaturity of neonates, A reduced GFR reduced concentrating ability and hence this has to be delayed until three months of age or interpreted with caution if performed earlier.

Functional assessment is performed with voiding, cysto, urethra, radioisotope or MR Urogram.

Postnatal Ultrasound Evaluation

In terms of postnatal ultrasound evaluation, this is a first line modality.

Imaging is performed through multiple planes and by using different probes, the linear array transducers, for example, can help in improve visualization of the renal pyramids.

Prone imaging can be used in kids to assess the, to get the accurate measurement of renal length and maximal AP diameter of the renal pelvis.

Doppler can be performed as it is increased in the intrarenal arterial resistance in obstruction in terms of void cy urethra as per the revised 2011 American Academy of Pediatrics guideline, only when ultrasound demonstrates bladder wall thickening or suggest urethral dilatation or high nephrosis scarring or other findings that suggest high grade SICO urethral reflux or obstructive pathology.

Should this be performed in terms of MRI and MR urogram, it allows a concurrent anatomical and functional evaluation without the use of analyzing radiation.

Gives superb intrinsic contrast and specia temporal resolution allowing for multiplanar three dimensional constructions.

It is limited by its cost availability and also the need for sedation for performing MRI in these small kids.

Postnatal Definition of Hydronephrosis

Postnatal definition of hydronephrosis is different for the pediatric radiologist compared to the pediatric urologist.

Pediatric radiologists tend to use descriptive terminology like mild, moderate, or severe hydronephrosis as seen in these cases, pediatric urologists prefer a semi, a quantitative or semi-quantitative assessment Which includes these grades grade zero to grade four as we discussed previously.

Case Reviews

Now to review some cases transient hydronephrosis, this may be related to narrowing of the UPJ or natural kinks of folds and that occur early in development and resolve as a patient matures.

This is seen in about 41 to 88% of cases most fetuses with a PD less than six millimeters in the second trimester and less than eight millimeters in the third trimester have transient hydronephrosis.

This is an example of a 22 week old fetus with bilateral pelvic ais measuring 5.4 millimeters and six millimeters, but a follow-up ultrasound performed at 33 weeks shows resolution of the ectasis with renal pelvis now measuring three millimeters.

UPJ Obstruction

Next case of UPJ obstruction seen in about five to 64% of cases seen as pelvic pelvic lal dilatation without uretal dilatation.

Postnatal surgical intervention rate is about 19 to 52%.

There is an increased incidence of other urological abnormalities including VUR Multicystic dysplastic kidney with UI G obstruction.

This is a prenatal image from a 26 week old fetus with right-sided pelvic ectasis with glacial dilatation suggesting UTDA two or a three and a postnatal image of the same.

Fetus shows that there is severe hydronephrosis on the right kidney, which is UTDP three

Vesicoureteral Reflux (VUR)

Persico uteral reflux presents with hydronephrosis or hydroureter nephrosis.

There are no reliable antenatal findings to definitively diagnose VUR.

The incidence of reflux appears to increase with the degree of sonographic dilatation postnatally.

However, the degree of dilation does not correlate with the grade of VUR normal PA postnatal ultrasound also does not exclude VUR.

This is a postnatal ultrasound showing C severe hydronephrosis with dilatation of the caly and cortical thinning the VCU gene.

This P shows reflux into the left ureter reaching up to the kidney, suggesting a grade four or five reflux.

Another case ultrasound of the left kidney in prone showing mild HI nephrosis with dilation of the left ureter.

VCUG In this patient shows grade two three reflux into the left ureter and not into the kidneys

UVJ Obstruction and Megaureters

UVJ obstruction and mega ureters.

There's prenatal hydronephrosis, urethral dilatation and normal bladder would suggest a mega ureter.

This can be refluxing, can be obstructed, non refluxing, non obstructed and refluxing obstructed majority resolves spontaneously during postnatal follow-up

Multicystic Dysplastic Kidneys (MCDK)

Multicystic dysplastic kidneys are seen as multiple non communicating cyst of various sizes and there is no evidence of identifiable renal parenchyma in these cases.

MCDK can be confused with UPG obstruction.

This is a prenatal ultrasound in the 27 week old fetus with absent left kidney which was replaced with multiple cyst suggesting a multicystic dysplastic kidney postnatal ultrasound in the same fetus showed a smaller size of the multicystic dysplastic kidney with smaller size of multiple cyst uro atrophy.

Posterior Urethral Valves or Urethral Atresia

Imaging findings in posterior urethral valves or urethral atresia include prenatal hydronephrosis which is often bilateral dilated thick wall bladder that fails to empty a dilated posterior urethra and decreased amniotic fluid due to the obstruction.

This carries a worse prognosis with increased mortality and morbidity due to pulmonary hypoplasia renal damage.

Prenatal ultrasound in this speed shows bilateral hydronephrosis with echogenic appearance of the kidneys and a dilated bladder with a keyhole appearance.

Postnatal appearance in the same PA fetus showing severe hydronephrosis with dilated thick wall bladder debris was seen in the bladder and bilateral ureters were dilated as well.

Ureterocele and Ectopic Ureters

In terms of urethrocele and ectopic ureters, this is an example of a patient prenatally showing dilated uh, duplicated collecting system in the right kidney with a normal left kidney bladder was not well seen as it was distended.

Postnatal images in the same fetus confirmed a duplicated collecting system with a cystic structure seen in the bladder likely a roal.

Another case showing a prenatal ultrasound in 27 week fetus showed mild pelvic cases in the left kidney.

We recommended postnatal follow-up.

Postnatal follow-up showed a duplicated collecting system in the left kidney with a dilated left ureter and there was dilated ureter seen posterior to the bladder as well.

VCUG in the same patient showed abnormal low insertion of the left ureter with reflux seen into the dilated left ureter.

Urinary Tract Dilatation (UTD) Classification

Now to move on to the new urinary tract dilatation or UTD classification due to the need for a unified classification system with an accepted standard terminology for the diagnosis and management of prenatal and postnatal urinary tract.

D dilation UTD classification was proposed.

This was formed by a collaboration of eight societies with special interest in urinary tract dilatation.

This included American College of Radiology, A IUM, American Society of Pediatric Nephrology Society of Fetal Urology Society of for Maternal Fetal Medicine, society for Pediatric Urology Society for Pediatric Radiology and a Society for Radiologists and Ultrasound.

They proposed a unified description of ary tract dilation to be applied prenatally and postnatally.

They provided a standardized scheme for prenatal evaluation of patients based on the ultrasound criteria and this is only to be used in isolated ate tract dilatation.

Prenatal Assessment in UTD Classification

In terms of the prenatal assessment, fetal age less than 16 to 27 weeks less than four millimeters was considered as normal, greater than 28 weeks, less than seven millimeters was considered normal and then postnatally less than 10 millimeters was considered as normal.

There are different parameters used in CLASSIFI in the UTD classification.

The first one is anterior posterior renal pelvic diameter which is measured on transverse image at the maximal diameter of the intrarenal pelvis.

Next escalation dilatation which can be central or peripheral parenchymal thickness which is a subjective assessment.

Parenchymal appearance to evaluate the echogenicity cortico medullary differentiation and assess for cortical cyst.

The ureters as to the presence of dilation of the ureter bladder to evaluate the wall thickness presence of urethral seals of dilated posterior urethra in a fetus that is between 16 to 27 weeks, four to seven millimeters with central or no collation dilatation would be considered a UTD one A one or lower risk patient as shown in this example here with dilation of the renal pelvis on the right of 4.7 millimeters, which is a UT D one, but on the left of 12.5 millimeters which would be UT DA two A three, so greater than seven millimeters or if there's any peripheral collation dilatation, parenchymal thickness abnormalities, abnormal parenchymal appearance, normal uric or bladder appearance and unexplained hydro oligohydramnios would be considered UTD 8 2 3 which is increased risk

In fetuses that are greater than 28 weeks greater than seven millimeters with no central ocion dilatation would be considered a one or lower risk as shown in this particular patient, which is 35 e cold fetus with bilateral hydronephrosis but only with central coasal dilatation suggesting UTDA one if the renal pelvis measures greater than 10 millimeters or there's presence of any of these described abnormalities, that is per peripheral cosal dilatation, parenchymal thickness abnormalities, parenchymal appearance abnormalities, abnormal ureters or bladder and an unexplained oligohydramnios would be considered as UTD eight to three.

With that is increased risk.

Postnatal Assessment in UTD Classification

In terms of uh, postnatal assessment, ultrasound has to be performed after 48 hours after birth, 10 to 15 millimeters with just central cosal dilatation would be considered UTDP one or lower risk 10 to 15 millimeters or greater than 15 millimeters and with peripheral cosal dilatation or uh, abnormal ureters would be considered UTD P two or with intermediate risk greater than 15 millimeters or between 10 to 15 millimeters, but with peripheral cosal dilatation, PRI parenchymal thickness abnormalities, parenchymal appearance abnormalities, abnormal bladder or ureters would be considered UT DP three or high risk.

Management and Follow-Up

Prenatal Management

Now moving on to management in terms of prenatal assessment, if a fetus is diagnosed with UTDA one and the fetus is less than 32 weeks, a follow-up should be performed after 32 weeks.

If there is resolution of the dilatation with normal appearance of the parenchyma bladder and ureters, no further prenatal or postnatal follow-up is recommended.

If there's persistent TDA one or it changes to TDA two postnatal evaluation between 48 hours and one month and then a follow-up ultrasound and one to two, one to six months later is recommended.

If a fetus has UTD eight, two or three, a follow-up ultrasound in four to six weeks is recommended and then further follow-up is at the discretion of the clinic.

The physician postnatal follow-up greater than 48 hours and before one month or significant or sooner in significant neuropathies is recommended.

Postnatal Management

In terms of postnatal management UTDP one, which is mild nephrosis, a follow-up ultrasound in one to six months is recommended and then further evaluation is performed at clinical discretion In terms of UT DP two, follow-up ultrasound in one to three months is recommended and then A-V-C-U-G and prophy attic antibiotics can be started at the discretion of the clinician.

In terms of UTD P three, follow up ultrasound in one month and VCUG and prophylactic antibiotics are written, antibiotics are recommended, so in terms of reporting there are seven imaging parameters that are to be considered there.

Anterior posterior renal pelvis diameter, glacial dilatation, parenchymal thickness, parenchymal appearance, ureter, bladder, and unexplained hydro oligohydramnios.

This is a macro that we use at the University of Washington to report antenatal or postnatal hydronephrosis and the impression then recommends the type of UUTD and a recommendation for management is provided as well.

Conclusion

Thank you very much.