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220 J. C. Veille
Fetal Renal Artery and Fetal Anomalies
Renal Agenesis
Pregnancies associated with early oligohydramnios
have a poor prognosis. The fetal anatomy is particularly
difficult to assess because the acoustic window
is notoriously poor. In cases of bilateral renal agenesis,
the fetal renal arteries are absent.
We identified a case of absent renal arteries using
color Doppler transvaginal ultrasonography in a fetus
with severe oligohydramnios. This 18-week pregnancy
was complicated by severe oligohydramnios. Abdominal
ultrasonography was not adequate to evaluate the
fetal anatomy, including the presence or absence of
kidneys. Using a transvaginal color Doppler ultrasound
technique, the abdominal aorta was identified
but the renal arteries were not. The fetus subsequently
died in utero, and postmortem examination
confirmed the ultrasonic finding of bilateral renal
agenesis (Fig. 15.8).
MarÉ—l et al. reported similar findings in a group
of 14 fetuses during the second trimester in which
there was oligohydramnios and a strong suspicion of
renal agenesis on ultrasound recordings. Using a color
ultrasound technique, the renal arteries were properly
identified in six of eight cases, in which normal
kidneys were found at postmortem examination. In
all six cases of complete renal agenesis proved at autopsy
they could not properly identify the renal artery
[57].
It is of utmost importance to recognize that the
presence or absence of color is angle-dependent. If
the Doppler signal is perpendicular to the flow of
blood, there is no Doppler shift and therefore no color.
Thus an erroneous diagnosis could easily be made
if this Doppler principle is violated.
Pyelectasis
Fetal pyelectasis may affect renal blood flow. In one
study, Kara et al. compared the RIs in the fetal interlobar
renal arteries (IRAs) of third-trimester fetuses
with or without pelvicaliceal dilatation of up to
10 mm with those of full-term healthy infants [58].
They studied three groups according to the anteroposterior
diameter of the renal pelvic dilatation:
group 1, no dilatation; group 2, 1±5-mm dilatation,
and group 3, 6±10-mm dilatation. The IRA of both
kidneys were obtained in 139 of the fetuses (Table
15.4). The RI in the fetal IRA did not differ in fetuses
with and without renal pelvic dilatation of up to 10
mm. The authors concluded that an increase in the
RI of fetuses that have a mild degree of pyelectasis
should be investigated further for possible renal
pathology.
Color Doppler Ultrasonography
and Fetal Renal Obstruction
Bates and Irving reported on color Doppler imaging
of the fetal renal artery in 29 fetuses who had either
unilateral or bilateral significant urinary tract dilatation
[59]. Although they initially hypothesized that
fetal renal obstruction could be detected by analysis
of the Doppler waveforms, their study failed to confirm
any abnormality of the PI in these fetuses.
Fetuses with hydronephrosis secondary to a ureteropelvic
junction (UPJ) obstruction were followed
up after birth. Using a uroradiology database (1994
through 1999) Rooks and Lebowitz identified children
who had a surgically corrected UPJ obstruction from
intrinsic and extrinsic causes. These authors identified
100 who had symptomatic UPJ obstruction and
who were treated with surgery. In 11 of these cases
(11 %), the obstruction was caused by a crossing vessel.
Extrinsic UPJ obstruction caused by a vessel is an
uncommon cause of obstruction when all patients are
considered, but fetal color Doppler should be included
in all cases of UPJ obstruction found on prenatal
sonography [60].
Fig. 15.8. Transvaginal color ultrasonogram of an 18-week
fetus with severe oligohydramnios and for whom the transabdominal
scan was not informative. This transvaginal color
ultrasound scan showed the abdominal aorta and the
absence of fetal renal arteries, strongly suggesting bilateral
renal agenesis. The postmortem examination confirmed
the ultrasound diagnosis
Table 15.4. Resistance index (RI) in fetuses with and without
renal pelvic dilatation [58]
Group 1
No dilatation
Group 2
1±5 mm
Group 3
6±10 mm
Number 172 98 47
RI-X ÔSD 0.81 Ô0.09 0.80Ô0.07 0.80Ô0.06