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a Chapter 15 Pulsed Doppler Ultrasonography of the Human Fetal Renal Artery 221
Multicystic Fetal Kidneys
The diagnosis of multicystic kidney in utero can be
made with reasonable reliability with real-time sonography.
However, a cystic hydronephrotic kidney may be
difficult to distinguish from a multicystic kidney, necessitating
postnatal renography. Gill et al. reported
their observations of Doppler waveform variation in
cystic fetal kidneys [61]. Five consecutive fetuses with
a unilateral cystic kidney and one with a unilateral hydronephrotic
duplex kidney and cystic upper moiety
were evaluated in utero with color Doppler renal sonography.
The Doppler signal on serial ultrasound was
consistently absent in the ipsilateral cystic kidney,
while normal renal artery Doppler waveforms with a
systolic and diastolic component were obtained from
the contralateral and unaffected moieties. Postnatal renography
confirmed nonfunction in all cystic moieties.
The hydronephrotic noncystic moiety of the duplex
kidney showed a normal Doppler waveform and good
function. Thus absence of renal artery Doppler waveforms
in fetal cystic kidneys correlates with renal nonfunction
suggesting that fetal Doppler sonography
could be an additional tool to diagnose confidently a
multicystic kidney in utero [61].
Fetal Artery Waveforms
and Meckel Syndrome
Hata et al. reported on the results of PW Doppler examination
of the fetal renal artery of a 21-week-old fetus
affected by occipital encephalocele and polycystic dysplastic
kidneys [62]. PW Doppler sonography showed
an increase in the diastolic component of the velocity
waveform of the renal artery, causing the PI to be significantly
lower than in normal fetuses. They speculated
that this increase in renal ªperfusionº was probably
an expression of the enlarged kidney mass [62].
Quantitation of Fetal Renal Blood Flow
To date, one of the most valuable uses of duplex ultrasound
has been for quantitation of stroke volume
and cardiac output [63±68]. Doppler ultrasonography
estimates the average of all the blood velocities across
a vascular structure. If the size of the vascular structure
can be measured and assumed to be circular, the
area can be calculated. The product of the time velocity
integral (TVI), the cross-sectional area of the vascular
structure (A), and the heart rate (HR) has been
shown to represent the volume of blood flow moving
through that structure. The PW Doppler waveform
also reflects ventricular contractility.
Flow ˆ TVI A HR
Analysis of the upward swing of the initial part of
the curve has been correlated with ventricular systolic
function. Stated another way, the time from the beginning
of the Doppler curve to the peak of the curve can
be measured and correlates with systolic ventricular
performance [66]. Thus Doppler sonography is able
not only to quantify blood flow through individual vascular
structures but also to assess ventricular contractility.
A typical Doppler waveform is shown in Fig. 15.9.
Volume estimates obtained using Doppler techniques
have been shown to correlate well with both
the Fick and thermodilution methods for estimating
Fig. 15.9. Fetal human renal
artery has high peak systolic
velocity and low end-diastolic
velocity, resulting in a high
systolic/diastolic ratio and
pulsatility index. The time
velocity integral (TVI) is
shown in the hatched area.
The TVI is multiplied by the
area of the renal artery to estimate
the renal blood flow