Diagnostic ultrasound ( PDFDrive )

1366 PART IV Obstetric and Fetal Sonography
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B
FIG. 39.39 Bladder Exstrophy. (A) Longitudinal scan of the lower fetal abdomen in a 29-week fetus shows an irregular mass on the anterior
abdominal wall (arrows), below the umbilical cord insertion (U). A luid-illed bladder was not identiied. Note normal amniotic luid volume. (B)
Corresponding photograph shows the exposed bladder (arrows) below the umbilical cord (U).
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B
FIG. 39.40 Normal Genitalia. (A) Normal 19-week male fetus. Transverse scan of the perineum shows the penis and scrotum. (B) Normal
19-week female fetus. Transverse scan of the perineum shows the labial folds.
of bladder, imperforate anus, and spinal defects. Renal anomalies
and abnormalities of the lower limbs are oten present. 242,243
THE GENITAL TRACT
Normal Genitalia
Fetal sex determination has medical as well as social implications.
hese include (1) history of X-linked disorders, (2) assignment
of dizygosity in twin pregnancies, (3) exclusion of maternal cell
contamination during amniocentesis or chorionic villous sampling,
(4) need to conirm fetal gender to diagnose certain
structural abnormalities (e.g., posterior urethral valves, ovarian
cysts), and (5) familial syndromes in which genital abnormalities
are common.
In the second trimester, fetal sex determination is based on
direct visualization of the external genitalia: the penis and
scrotum in males, and the labia majora and minora, represented
by two or four parallel lines, respectively, in females (Fig. 39.40).
Inopportune fetal position, oligohydramnios, maternal obesity,
and operator inexperience represent the major limitations in
fetal gender assessment. Errors may occur when the rounded,
apposed labia are mistaken for a small, empty scrotum or when
the umbilical cord is mistaken for the penis. he accuracy of
fetal sex determination ranges from 92% to 100%. 244 When
conventional methods fail or in the setting of ambiguous genitalia,
fetal sex can be assigned by sonographic evaluation of the pelvic
organs in the second and third trimesters of pregnancy. 245 It has
been reported that measurement of the distance between the
posterior wall of the fetal bladder and the anterior wall of the