radiologic diagnosis of fetal hydronephrosis

Sabrina Vineberg, HMS IIIGillian Lieberman, MD

Radiologic Diagnosis of Fetal Hydronephrosis:

Associated Abnormalities and Fetal Outcome

Sabrina Vineberg, Harvard Medical School, Year IIIGillian Lieberman, MD

March 2003

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Fetal Imaging Modalities• Ultrasound:

– Fast and safe (no ionizing radiation)

– Allows for good visualization of fetal anatomy and live, real-time imaging

– Efficient method to survey for fetal anomalies

• MRI:– Better soft tissue contrast

for characterization of anomalies

– Better than US in patients with oligohydramnios

– Currently no known adverse effects

BIDMC PACS

Levine D. and R. R. Edelman. Abdominal Imaging. 22: 589-596, 1997.

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Diagnosis of Fetal Hydronephrosis on Ultrasound

• Index patient:– Mrs. S. is a 34 y.o. G2P1 who presented to

BIDMC at 29+6 weeks GA for a follow-up fetal ultrasound after a routine fetal survey at an outside hospital documented unilateral fetal hydronephrosis.

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Mrs. S.’s UltrasoundSpine

Left kidney, sagittal view Right kidney, sagittal view

*

**

*

*

*

** = dilated renal pelvis

Transverse view Sagittal view

R

L

R

L

Calyceal dilatation

US findings: mild hydronephrosis on the right with central dilatation of 8-9 mm and severe hydronephrosis on the left with a large extrarenal pelvis measuring 2.8 cm

All images from BIDMC PACS

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Normal Fetal Kidneys

S = spine

Kidneys outlined by arrowheads

• Fetal kidneys are ovoid bilateral paraspinous structures:

- Renal pelvis – “slit-like” lucency within central portion of kidney.

- Medulla – hypoechoic regions surrounding renal sinuses.

- Cortex – thin and difficult to visualize on US.

- Retroperitoneal fat – echogenic density surrounding kidneys.

Gabbe: Obstetrics - Normal and Problem Pregnancies, 4th ed., Copyright © 2002 Churchill Livingstone, Inc.

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Renal Development Timeline and Important Structures

• Ureteral bud (week 4) → mesoderm, arises from oupouching of mesonephric/Wolffian ducts, opens into urogenital sinus. Gives rise to ureter, renal pelvis, calyces and collecting system

• Metanephric cap (week 5-6) → mesoderm, interacts with structures of ureteral bud to form functional renal parenchyma

• Cloaca (week 4) → endoderm, divides into urogenital sinus (cranial) and anorectal canal (caudal). Urogenital sinus gives rise to bladder and urethra

• Fetal kidneys begin to function at the start of the 2nd

trimester. By week 16-18 they become the major source of amniotic fluid for the fetus

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Renal Development

Week 6 Week 8 Week 10

Migration of the fetal kidneys

Urogenital Sinus

Ureteric bud

Metanephric cap

Embryo 5-6 weeksMesonephric Duct

Sweeney, Lauren J. Basic Concepts in Embryology. A Student's Survival guide. New York: The McGraw-Hill Companies, 1998.

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Fetal AnatomyBladder

KidneySpleen

Iliac WingLiver

Lungs

Amniotic fluid

Nyberg, David A., Barry S. Mahony and Dolores H. Pretorius. Diagnostic Ultrasound of Fetal Anomalies: Text and Atlas. Chicago: Year Book Medical Publishers, 1990.

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Hydronephrosis• Hydronephrosis (HN) → dilatation of the pelvis

and/or calyces of the kidney• Diagnosis of fetal HN is increasing with increased

use of ultrasound in pregnant women• 1-2% of pregnancies may show evidence of HN,

and it accounts for 50-75% of prenatally diagnosed renal abnormalities.

• Degree of dilatation required for diagnosis of HN varies with gestational age, and is determined using the anteroposterior diameter of the renal pelvis.

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Measuring Renal Dilatation•Anteroposterior diameter (APD): Size of the renal pelvis measured in the anterior → posterior direction on a transverse view through the abdomen.

•For a diagnosis of hydronephrosis, APD must be greater than:

- 6mm at < 20 weeks GA

- 8 mm at 20-30 weeks GA

- 10mm at > 30 weeks GAClose-up of a mildly dilated right

fetal kidney on ultrasound(short arrows outlining kidney)

S = Spine

APD

Image from BIDMC PACS

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Grades of Fetal Hydronephrosis

Gloor, J.M. Mayo Clinic Proceedings. 70: 145-152, 1995

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Natural History of Fetal Hydronephrosis

• Most cases of prenatally diagnosed HN (~90%) will resolve spontaneously before birth or after delivery.

• Of those cases that do not resolve on their own, the majority are amenable to surgical or medical correction after delivery.

• Surgery is best performed within the first year of life to minimize irreversible damage.

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Causes of Fetal Hydronephrosis• Physiologic:

– Urine production 4-6x greater before delivery– Increased compliance of fetal ureter– Partial/transient obstructions associated with development

• Pathologic:– Almost always due to obstruction, which can occur anywhere in

the urinary tract– Degree of dilatation depends on the severity and location of

obstruction– Severe or longstanding obstruction of the urinary tract can lead to

permanent renal damage and to systemic problems for the fetus– Non-obstructive causes of HN include vesicoureteric reflux

(VUR), prune belly syndrome and renal cysts.

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Radiologic Findings• Can be unilateral or bilateral• Severity of dilatation depends on the level of

obstruction. Common locations include:– Ureteropelvic junction → most common location of obstruction– Vesicoureteral junction → with or without reflux– Vesicouretheral junction → often due to posterior urethral valves

• Renal parenchymal changes• Amount of amniotic fluid:

– With severe obstruction and renal atrophy, the fetus can’t produce or excrete amniotic fluid, leading to oligohydramnios

– Oligohydramnios is a poor prognostic sign for the fetus → risk of pulmonary hypoplasia - lack of amniotic fluid causes compression of fetal lungs which prevents lung development.

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Radiologic Findings – US Dilatation of Renal Pelvis and Calyces

• Patient A: Follow-up US for known HN, 27 weeks GA

– US Report: “Worsening bilateral central renal collecting system dilatation, left greater than right, which is out of proportion to caliectasis and suggests UPJ obstruction”.

• Patient B: Routine fetal survey, 22 weeks GA

– US report: “Mild bilateral hydronephrosis. Follow-up is recommended in six weeks and post partum.”

Spine

Patient A - Transverse view

Patient B - Sagittal view

Calyceal dilatation


R. kidney L. kidney

* = dilated renal pelvis

**

**

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Radiologic Findings – US Dilatation of Renal Pelvis and Ureters

• Patient C: US with biophysical profile for post-dates at 40 weeks GA

– US report: “Bilateral hydroureteronephrosis. Follow up study of the kidneys is recommended after the baby is born”.

• Patient D: Routine fetal survey, 28 weeks GA

– US Report: “Central renal dilatation of 11 mm on the left and 8 mm on the right, out of proportion to caliceal dilatation along with intermittent visualization of the ureters, which appear mildly dilated. Findings are suggestive of vesicoureteral reflux”.

Patient C - Transverse view Patient C – L. ureter

Patient D - Sagittal view

Ribs

Spine

Dilated ureter

Dilated ureter

*

*Aortic bifurcation

***

Spine

Kidneys

All images from BIDMC PACS* = dilated renal pelvis

Dilated ureter

Bladder

Kidney

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Radiologic Findings - MRI

K

A

P

T2W MRI scan at 32 weeks GA showing moderate fetal HN

Fetal Brain

Sagittal MRI showing severe HN in a 33 week old fetus with

obstruction due to posterior urethral valves. US study limited

by severe oligohydramnios.

K= maternal kidney

A = amniotic fluid

P = placenta

Dilated fetal kidneyFetal kidneys

Spine

Fradin, J.M. et al. Urology. 53:825-827, 1999. Miller, O.F. et al. The Journal of Urology. 168:1158-2259, 2002.

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Amount of Amniotic FluidNormal amniotic fluid

Normal fetus

Severe oligohydramniosFetus with renal agenesis


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Why is prenatal diagnosis important?

• With severe obstruction and oligohydramnios:– Fetus at risk of renal dysplasia and pulmonary

hypoplasia which is often fatal– Prenatal intervention can be lifesaving:

i. Percutaneous fetal shunt catheters – a route for amniotic fluid to leave the urinary tract and return to the amniotic cavity

ii. Surgical exteriorization of fetal urinary tract

• Knowledge of moderate→severe cases of HN antenatally allows for appropriate follow-up and prompt correction after birth

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Management of Hydronephrosis In the Fetus and Neonate

Callen, Peter W. Ultrasonography in Obstetrics and Gynecology. 2nd ed. Philadelphia: WB Saunders Co., 1988.

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Management of Hydronephrosis in the Neonate

• Prophylactic antibiotics to prevent UTI and pyelonephritis associated with reflux

• Follow-up ultrasound, at least 72 hours after birth

• Other imaging studies include voiding cystourethrogram (VCUG) or DMSA scan

• Prompt surgical correction of obstruction if necessary, to prevent irreversible renal parenchymal damage

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Radiologic Work-up of Hydronephrosis in the Neonate

• Radiologic imaging of a newborn diagnosed with hydronephrosis in utero:

– US: Bilateral dilatation of the renal collecting system

– VCUG: Significant reflux bilaterally– DMSA scan: Decreased uptake bilaterally,

L>R

Right kidney Left kidney

Voiding cystourethrogram DMSA scan

Ultrasound

All images from ACR Pediatric Learning File, 1998.

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References• American College of Radiology Pediatric Learning File. Version 2.02. CD-ROM. ACRI Software Development, 1998.• Callen, Peter W. Ultrasonography in Obstetrics and Gynecology. 2nd ed. Philadelphia: WB Saunders Co., 1988.• De Bruyn, R. and I. Gordon. Postnatal investigation of fetal renal disease. Prenatal Diagnosis. 21: 984-991, 2001.• Fradin, J.M. et al. Hydronephrosis in pregnancy: simultaneous depiction of fetal and maternal hydronephrosis by magnetic resonance

urography. Urology. 53:825-827, 1999.• Gabbe, Steven G., Jennifer R. Niebyl and Joe Leigh Simpson. Gabbe: Obstetrics - Normal and Problem Pregnancies. 4th ed. New

York: Churchill Livingstone, 2002.• Gloor, J.M. Management of Prenatally Detected Fetal Hydronephrosis. Mayo Clinic Proceedings. 70: 145-152, 1995.• Levine, D. and R.R. Edelman. Fast MRI and its application in obstetrics. Abdominal Imaging. 22: 589-596, 1997.• Miller, O.F. et al. Diagnosis of urethral obstruction with prenatal magnetic resonance imaging. The Journal of Urology. 168:1158-

2259, 2002.• Mouriquand, P.D.E. et al. Pathophysiology, diagnosis and management of prenatal upper tract dilatation. Prenatal Diagnosis. 21:

942-951, 2001.• Nyberg, David A., Barry S. Mahony and Dolores H. Pretorius. Diagnostic Ultrasound of Fetal Anomalies: Text and Atlas. Chicago:

Year Book Medical Publishers, 1990.• Poutamo, J. et al. Diagnosing fetal urinary tract abnormalities: benefits of MRI compared to ultrasonography. Acta Obstetricia et

Gynocologica Scandinavica. 79: 65-71, 2000.• Sairam, S. et al. Natural history of fetal hydronephrosis diagnosed on mid-trimester ultrasound. Ultrasound in Obstetrics and

Gynecology. 17: 191-196, 2001.• Shokeir, A.A. and R.J.M. Nijman. Antenatal hydronephrosis: changing concepts in diagnosis and subsequent management. BJU

International. 85: 987-994, 2000.• Sherer, D.M. Is fetal hydronephrosis overdiagnosed. Ultrasound in Obstetrics and Gynecology. 16: 601-606, 2000.• Sweeney, Lauren J. Basic Concepts in Embryology. A Student's Survival guide. New York: The McGraw-Hill Companies, 1998.

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Acknowledgements

• Gillian Lieberman, MD• Pamela Lepkowski• Deborah Levine, MD• Tejas Mehta, MD• Joseph Makris, MD• Dan Saurborn, MD• Larry Barbaras and Cara Lyn D’amour

radiologic diagnosis of fetal hydronephrosis

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