Diagnostic ultrasound ( PDFDrive )

1342 PART IV Obstetric and Fetal Sonography
A
B
FIG. 39.4 Magnetic Resonance Images of Normal Kidneys. T2-weighted magnetic resonance images at (A) 23 weeks’ gestation and (B) 30
weeks’ gestation. The renal parenchyma (arrows) shows low to intermediate signal intensity. The renal collecting system and bladder (B) shows
high signal intensity. S, Stomach.
abnormalities (polycystic kidney disease, renal agenesis or
adysplasia), because it may help to diagnose the type of polycystic
kidney disease in the fetus, detect asymptomatic renal pathology
in parents (and siblings), and counsel parents regarding the
recurrence risk. 34-36
Fetal magnetic resonance imaging (MRI) may be used as
an adjunctive imaging modality for improving diagnostic accuracy
of UT abnormalities. 37,38 It may help to identify the kidneys when
sonographic visualization is limited by anhydramnios (or severe
oligohydramnios) and large maternal body habitus (Fig. 39.4). 39,40
Finally, with the advent of difusion-weighted imaging, the
measurement of water apparent difusion coeicient has shown
promise in diferentiating between normal and abnormal renal
parenchyma, which could serve as a noninvasive method of
assessing fetal renal function. 41,42
Evaluation of the Fetal Urinary Tract
BLADDER
Presence
Appearance and size
KIDNEYS
Presence
Number
Position
Appearance (echogenicity, cysts)
Unilateral or bilateral
COLLECTING SYSTEM
Dilation
Level of obstruction
Cause of obstruction
Unilateral or bilateral
FETAL GENDER
Bilateral Renal Agenesis
Bilateral renal agenesis is a lethal congenital anomaly with an
incidence of approximately 1 in 4000 births and a 2.5 : 1 male
preponderance. 43,44 he ureteric buds fail to develop; thus the
kidneys are absent. Because no urine is produced, severe oligohydramnios
or anhydramnios results. Pulmonary hypoplasia is
the major cause of neonatal death. Other features of “Potter’s
sequence” include typical facies (beaked nose, low-set ears,
prominent epicanthic folds, hypertelorism), limb deformities,
and IUGR.
he ultrasound indings include severe oligohydramnios or
anhydramnios and nonvisualization of the kidneys and bladder.
Before 16 weeks’ gestation, AFV is not dependent on urine
production and may be normal despite absent renal function.
he absence of fetal kidneys should be the most speciic inding,
but this may be diicult to document because of poor image
quality associated with oligohydramnios. In addition, bowel or
adrenal glands in the renal fossae may be mistaken for kidneys. 45
However, recognition of the distinctive, lattened appearance of
the adrenal gland on longitudinal sonogram (“lying down”
adrenal sign) helps to conirm that the kidney did not develop
in the lank 46 (Fig. 39.5, Video 39.1).
Repeated and consistent nonvisualization of the urinary
bladder (over 1 hour) is a secondary sign of bilateral renal agenesis
(Fig. 39.6). Conversely, identiication of a normal bladder excludes
this diagnosis. A small urachal diverticulum may mimic the
bladder, but its lack of illing and emptying distinguishes it from
the bladder. A major challenge is to reliably distinguish between
fetuses with bilateral renal agenesis and those with impaired
renal function from severe uteroplacental insuiciency or IUGR.
Several techniques have been proposed to improve visualization
of fetal structures: intraamniotic and intraperitoneal infusion of
isotonic saline, 47 transvaginal ultrasound, 48 and color Doppler
ultrasound imaging. 49,50 he transvaginal probe is particularly
useful in the second trimester and with breech presentation (Fig.
39.6, Video 39.2). Color Doppler imaging can be used to diagnose