Genito-urinary Imaging
Pre-natally Detected Fetal Genito-urinary Anomalies Philippe Chu, MD,1
Razia Rehmani, MD2 and Nalini Kanth, MD3
1. Attending Radiologist, North Shore-Long Island Jewish Health System; 2. Resident, Radiology, Nassau University Medical Center; 3. Residency Program Director, and Attending Radiologist, Nassau University Medical Center
Abstract
Pre-natal sonography is a useful screening tool for identifying fetal genito-urinary anomalies. The detection of such anomalies will influence management and interventions that may be required to reduce fetal morbidity and improve survival. Routine screening sonography can help identify those pregnancies that may require short-term follow-up. Sonographically detectable fetal genito-urinary anomalies include renal agenesis (unilateral, bilateral) and ectopia (pelvic kidney), obstructive uropathy (ureteropelvic junction obstruction, ureterovesical junction obstruction, congenital megaureter, posterior urethral valves), and cystic renal disease (autosomal recessive kidney disease, multicystic dysplastic kidney disease, autosomal dominant kidney disease, cystic renal dysplasia).
Keywords Fetal, genito-urinary, anomaly, screening, ultrasound
Disclosure: The authors have no conflicts of interest to declare. Received: June 29, 2010 Accepted: September 13, 2010 Citation: US Radiology, 2010;3(1):61–4 Correspondence: Philippe Chu, MD, North Shore–Long Island Jewish Health System, 900 Franklin Avenue, Valley Stream, NY 11580. E:
philippe.chu@
gmail.com
Pre-natal sonography is a useful screening tool for detecting a variety of fetal genito-urinary anomalies. Recognition of such anomalies helps to direct appropriate management and greatly affects the long-term outcome of the pregnancy. Accurate diagnosis of anomalies provides an opportunity for referral to appropriate services and counseling. In some instances, in utero surgical intervention or elective termination of pregnancy may be indicated. Routine sonography at 18–20 weeks of gestation provides a time-frame in which management strategies can be employed to improve survival or reduce morbidity, especially if the legal option of termination of pregnancy is not desired.1,2
Normal Anatomy
The normal fetal metanephric kidney begins urine production as early as the 10th week of gestation.3
be visible by ultrasound as early as 15 weeks of gestation.4
this period urine becomes a major component of the amniotic fluid.3
adjacent structures.
As the pregnancy progresses, the retroperitoneal fat increases in echogenicity and the renal contours become better defined.3
At this
time, the fetal kidneys appear as bilateral round structures on either side of the spine when imaged in the transverse plane (see Figure 1). By 20–25 weeks of gestation, the more echogenic renal cortex becomes distinct from the medulla.4
The kidneys should grow about
1 mm in length for each week of gestation throughout the second and third trimesters.3
© TOUCH BRIEFINGS 2011
The fetal kidneys and bladder can During
Early in the second trimester, the kidneys are isoechoic to
Renal Agenesis and Ectopia
The ureteral buds arise from the wall of the mesonephric duct at the margins of the cloaca, growing cephalad in the sacral region during the fifth week of gestation. The buds continue to grow until they contact the metanephric blastema, where cells are then induced to differentiate into the metanephric kidney. This occurs on each side of the fetus. Renal agenesis occurs when one or both of the ureteral bud(s) fail(s) to form.3
It can be associated with anomalies elsewhere in the genito-urinary tract. In males, it can accompany hypoplasia or agenesis of the testis and/or vas deferens on the ipsilateral side. In females, it can be associated with genital tract anomalies. On imaging, the colon can be seen occupying the renal fossa. There may also be compensatory hypertrophy of the contralateral kidney.
Unilateral renal agenesis occurs in one in 1,000 pregnancies and is usually not fatal.4
Bilateral renal agenesis occurs in one in 4,500–5,000 pregnancies.4 No fetal urine is produced in this condition, resulting in severe oligohydramnios and pulmonary hypoplasia by 20 weeks of gestation.3
This
condition is invariably fatal as amniotic fluid is vital for normal fetal lung development. A bell-shaped thorax is considered an ominous sign, as it suggests long-term oligohydramnios.4
Bilateral renal agenesis can be an
isolated finding or can be seen as part of a syndrome. In Potter syndrome, there is pulmonary hypoplasia, limb deformity, typical face face (wide set eyes, slightly compressed nose and chin, and low set flat ears), and ureteral absence.4
On imaging, there is absence of the renal outlines as well as of the bladder. Flat, discoid adrenal glands can be visualized in the
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