AJR 2003; 181:1381-1385
© American Roentgen Ray Society
MRI of Fetal Genitourinary Anomalies
Jacqueline T. Caire1,
Ronald M. Ramus2,
Kevin P. Magee2,
Bryan K. Fullington1,
David H. Ewalt3 and
Diane M. Twickler1,2
1 Department of Radiology, University of Texas Southwestern Medical Center, 5323
Harry Hines Blvd., Dallas, TX 75390-8896.
2 Department of Obstetrics and Gynecology, University of Texas Southwestern
Medical Center, Dallas, TX 75390-8896.
3 Perinatal Associates of Texas, Ste. 205, 8315 Walnut Hill Ln., Dallas, TX
75230-5104.
Received October 25, 2002;
accepted after revision May 22, 2003.
Address correspondence to D. M. Twickler
(diane.twickler{at}utsouthwestern.edu).
Abstract
OBJECTIVE. The objective of our study was to show examples of fetal
MRI evaluations of congenital genitourinary anomalies and to review the
embryology in relation to the MRI findings.
CONCLUSION. MRI was performed on 35 pregnant women with sonographic
findings that suggested that their fetuses had genitourinary anomalies.
Oligohydramnios or anhydramnios was identified in 22 of 35 women and did not
hinder visualization of anomalies. MRI allowed the amniotic fluid and the
presence, location, and morphology of kidneys and bladder to be assessed in
all fetuses at any stage of gestation and depicted sufficient anatomic detail
for us to evaluate the perineum in 27 of 35 pregnancies. Therefore, we found
MRI to be an excellent technique for revealing the anatomy of genitourinary
anomalies in the fetus.
Introduction
Anomalies of the genitourinary system are common, accounting for
14–40% of anomalies detected on prenatal sonography
[1,
2]. Sonography is an excellent
means of evaluating the fetal genitourinary tract
[1–6].
However, some factors, including the patient's body habitus and
oligohydramnios, can often prevent optimal assessment of anomalies of the
genitourinary system using sonography. MRI is gaining popularity for use in
evaluating suspected anomalies and has been performed on fetuses with
genitourinary abnormalities
[7–9].
The technique is especially valuable in imaging fetuses with abnormalities of
the genitourinary system that have resulted in oligohydramnios and in whom
lethal pulmonary hypoplasia is suspected; termination of pregnancy may be a
management option in such cases. In our article, we highlight the usefulness
of MRI in evaluating fetuses with suspected genitourinary abnormalities and
discuss the MRI findings of various types of genitourinary tract
dysmorphology.
Materials and Methods
Between January 2000 and June 2002, 35 pregnant women bearing 37 fetuses
(including two twin pregnancies, each of which consisted of one twin with a
suspected renal abnormality and one healthy twin) who had sonographically
suspected genitourinary anomalies or anhydramnios underwent MRI. The
gestational age of the fetuses ranged from 17 to 35 weeks, with 12 fetuses
having a gestational age of less than 24 weeks and 23 fetuses having a
gestational age of 24 weeks or more.
MRI was performed using a 1.5-T Signa magnet (General Electric Medical
Systems, Milwaukee, WI). A 15-sec localizer three-plane gradient-echo T2*
sequence was performed to plan the orthogonal planes relative to the fetal
lie. To obtain images, we used a single-shot fast spin-echo sequence with the
TR set as long as necessary to virtually eliminate T1-weighting and complete
the required acquisition. The parameters used were TR range/TEeff
range, 30,000–98,000/50–100; field of view, 12–36 cm;
matrix, 256 x 128 or 512 x 256; bandwidth, 31.2 or 62.5 kHz;
average number of excitations, 0.5; and slice thickness, 3–8 mm. A
surface coil was wrapped around the mother's pelvis and centered over the
fetal region of greatest interest. No maternal sedation was given because,
with acquisition times of 1.0–1.5 sec/slice, fetal sedation was not
necessary. Time needed for a complete acquisition sequence varied from 40 to
90 sec, depending on image quantity required. On average, seven MRIs (range,
five to nine) were acquired with a total average scanning time of 9–12
min. The orthogonal MRI planes were oriented in relation to the fetal lie. The
entire MRI study, including the setup, was completed within 30 min.
Informed written consent was obtained from each woman as part of an
indicated examination. Four areas were assessed in the fetuses during
retrospective image review: Amniotic fluid was qualitatively assessed as
normal or diminished on the basis of the ability to identify at least three
large pockets of fluid with a depth greater than 2 cm. The presence, location,
size, and appearance of the kidneys were assessed, and the size and appearance
of the bladder were evaluated. The fetal perineum was examined to confirm
whether the rectum and external genitalia could be identified. MRIs were
compared with neonatal outcomes, neonatal imaging studies, and pathology
results when available.
Results
In 22 of the 35 pregnancies, oligohydramnios or anhydramnios was present.
MRI diagnoses included renal agenesis (n = 7), unilateral or
bilateral multicystic dysplastic kidney (n = 7), ureteropelvic
junction obstruction with urinoma (n = 1), renal duplication with
ectopic ureterocele (n = 1), posterior urethral valves (n =
4), prune-belly syndrome (n = 1),
megacystis-microcolon–intestinal hypoperistalsis syndrome (n =
1), cloacal exstrophy (n = 2), anhydramnios with kidneys present
(n = 4), bilateral large solid kidneys (n = 1), renal
hypoplasia (n = 1), megaloureter (n = 1), bladder
enlargement with bilateral duplex collecting systems (n = 1),
urethral obstruction with patent urachus (n = 1), normal findings
(n = 1), and minimally conjoined ischiopagus (n = 1). In
addition, one fetus in a twin pregnancy had normal findings but its twin had a
multicystic dysplastic kidney.
With MRI, we were able to evaluate the quality of amniotic fluid and the
location and presence (or absence) of the kidneys and bladder in all fetuses
at any gestational age. Oligohydramnios or anhydramnios was present in 22 of
35 pregnancies studied but did not limit resolution in those cases. In four
patients with sonographically suspected renal agenesis, MRI revealed the
kidney despite the presence of anhydramnios. We were able to evaluate the
perineum on MRI in 27 of the 35 pregnancies, which was especially important in
fetuses with cloacal exstrophy or in cases in which fetal gender was essential
to making the correct diagnosis. The single-shot fast spin-echo sequence is a
relative T2-weighted sequence in which urine in the genitourinary system and
amniotic fluid are bright. Cystic dysplasias are also bright on T2-weighted
images.
Specific MRI findings related to the underlying embryology and
dysmorphology in fetuses were as follows:
Renal Agenesis
In our series, MRI showed oligohydramnios and allowed us to confirm
suspected renal agenesis on the basis of the inability to see the kidneys
[2,
4]. In one of the seven cases,
sirenomelia with a single lower extremity was present in addition to the renal
agenesis (Fig. 1A,
1B,
1C).
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Fig. 1A. —35-gestational-week-old fetus with suspected renal agenesis,
which occurs if metanephric diverticulum fails to develop or to penetrate
metanephric blastema. Coronal MRI obtained through fetus shows bright fluid in
stomach (white arrow) and psoas muscles (black arrows), but
no kidneys are identified.
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Fig. 1B. —35-gestational-week-old fetus with suspected renal agenesis,
which occurs if metanephric diverticulum fails to develop or to penetrate
metanephric blastema. Axial MRI of fetal abdomen reveals large anterior mass
thought to represent single abnormal lower extremity (large straight
arrow), but no kidneys, on either side of spinal column (small
straight arrow). Placenta (curved arrows) abuts fetus because of
anhydramnios.
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Fig. 1C. —35-gestational-week-old fetus with suspected renal agenesis,
which occurs if metanephric diverticulum fails to develop or to penetrate
metanephric blastema. Photograph of stillborn neonate displays appearance of
sirenomelia.
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Multicystic Dysplastic Kidneys
In our seven cases of multicystic dysplastic kidneys, diagnosis was based
on the high signal intensity of multiple cysts in one or both kidneys. If
bilateral cysts were seen and oligohydramnios was present, a lethal outcome
resulting from pulmonary hypoplasia was expected, which was the case for three
fetuses [1,
2]
(Fig. 2).
Congenital Ureteropelvic Junction Obstruction with Urinoma
In the one fetus with ureteropelvic junction obstruction, the obstruction
of urine flow from the renal pelvis into the ureter resulted in a dilated
renal pelvis that appeared bright on the single-shot fast spin-echo sequence.
The retroperitoneal urinoma had a similar signal intensity
[1,
2]
(Fig. 3).
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Fig. 3. —T2-weighted image obtained with single-shot fast spin-echo
sequence in 25-gestational-week-old fetus with left ureteropelvic junction
obstruction and retroperitoneal urinoma. Urine and urinoma appear bright.
Dilated left renal pelvis (arrows) is shown in axial plane, deviated
to midline by large urinoma (u).
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Renal Duplication with Ectopic Ureterocele
In the one fetus in whom renal duplication was found, the upper moiety of
the right ureter was dilated because of obstruction by an ectopic ureteral
insertion into the vagina. The lower moiety of the right pole of the kidney
had mild hydronephrosis that we believe was caused by bladder reflux
[1] (Fig.
4A,
4B,
4C,
4D).
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Fig. 4A. —30-gestational-week-old female fetus with duplicated right
collecting system, which is caused by second ureteral bud arising from
mesonephric duct. Coronal MRI obtained through fetus reveals that upper moiety
of pole is dilated on right (thin white arrows), whereas lower moiety
of right kidney pole displays mild dilatation of renal pelvis (thick white
arrow). Left kidney appears normal (black arrow).
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Fig. 4B. —30-gestational-week-old female fetus with duplicated right
collecting system, which is caused by second ureteral bud arising from
mesonephric duct. Sagittal MRI of perineum of fetus shows dilated ureterocele
in region of vagina (arrow) with associated ureteral dilatation
(arrowheads).
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Fig. 4C. —30-gestational-week-old female fetus with duplicated right
collecting system, which is caused by second ureteral bud arising from
mesonephric duct. Axial MRI obtained at level of perineum shows vaginal
ectopic ureterocele (large arrow) and thighs (small arrows)
anteriorly.
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Fig. 4D. —30-gestational-week-old female fetus with duplicated right
collecting system, which is caused by second ureteral bud arising from
mesonephric duct. Photograph shows neonate's external perineum with
ureterocele (arrows) pulled inferiorly by surgeon as well as
relationship of ureterocele to vaginal walls.
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Posterior Urethral Valves
In the four fetuses with posterior urethral valves, we observed a dilated
posterior urethra with varying amounts of amniotic fluid and varying degrees
of cystic changes in the kidneys. None of the four fetuses had dilated
ureters.
Prune-Belly Syndrome
In both fetuses with prune-belly syndrome, we found a massive bilateral
hydroureter with a distended abdomen. No evidence of posterior urethral
dilatation was seen.
Megacystis-Microcolon–Intestinal Hypoperistalsis Syndrome
Our study included a case of this rare syndrome in which the female fetus
had an enlarged unobstructed bladder with hydronephrosis and was surrounded by
normal amniotic fluid. The neonate died in the second month of life
[10] (Fig.
5A,
5B).
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Fig. 5A. —MRI of megacystis-microcolon–intestinal hypoperistalsis
syndrome in 30-gestational-week-old female fetus. b = bladder. Sagittal MRI
obtained through fetal abdomen and pelvis reveals massively dilated bladder
and renal hydronephrosis (arrow).
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Fig. 5B. —MRI of megacystis-microcolon–intestinal hypoperistalsis
syndrome in 30-gestational-week-old female fetus. b = bladder. Axial MRI
obtained through mid abdomen shows large bladder and bilateral hydronephrosis
(arrows).
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Cloacal Exstrophy
The characteristics of cloacal exstrophy include two hemibladders, which we
could identify on MRI. In this syndrome, external genitalia do not develop. We
identified a smooth perineum with an associated omphalocele and myelocystocele
of the lower spine in both fetuses. Myelocystoceles are different from
meningomyeloceles in that they are not considered open neural tube defects and
do not typically display Chiari's type II malformations of the central nervous
system [11], as was the case
in the fetus shown in Figure
6A,
6B,
6C,
6D,
6E.
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Fig. 6C. —34-gestational-week-old fetus with cloacal exstrophy.
Sagittal MRI obtained through fetus shows extensive fetal malformations
including myelocystocele (black arrow), hemibladder (white open
arrow), and omphalocele (white solid arrows).
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Fig. 6D. —34-gestational-week-old fetus with cloacal exstrophy. Coronal
T2-weighted image of lumbosacral spine shows dilated distal spinal canal with
bright signal, suggestive of myelocystocele.
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Discussion
We believe that ours is the largest series of MRI findings in suspected
fetal genitourinary abnormalities that has been reported. In our series, MRI
provided the anatomic detail that allowed for adequate assessment of the renal
and bladder regions and amniotic fluid in all fetuses at any gestational age.
Oligohydramnios or anhydramnios did not hinder MRI diagnosis. The appearance
of fetal urine in the genitourinary system and amniotic fluid is bright on
T2-weighted images. MRI aided in our assessment of the fetal perineum in many
of the fetuses in our study, which was helpful in the fetuses with cloacal
exstrophy and in cases in which gender was an important consideration for
diagnosis. MRI provided exquisite anatomic detail and thus was helpful in
determining fetal dysmorphology in most fetuses. MRI is a potentially useful
adjunct in the evaluation of fetal genitourinary anomalies.
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Abstract
Introduction
