Diagnostic ultrasound ( PDFDrive )

1346 PART IV Obstetric and Fetal Sonography
diagnosis, and angles less than 140 degrees are highly suggestive
of horseshoe kidney. 65 A horseshoe kidney is frequently associated
with other anomalies (e.g., urogenital, cardiac, skeletal, CNS)
and chromosomal abnormalities such as Turner syndrome,
trisomy 18, and trisomy 9. Isolated horseshoe kidney is a relatively
benign disorder that requires postnatal urologic follow-up because
of higher prevalence of VUR, renal calculi, UT infections, and
hydronephrosis.
Renal Cystic Disease
Renal cystic disease consists of a heterogeneous group of disorders
with inherited and acquired causes. Because of their diverse
etiology, histology, and clinical presentation, a widely accepted
classiication does not exist. he Potter classiication is based on
histology and does not take into account recent advances in
molecular genetics. 66 A more recent classiication based on the
genetic or nongenetic origin of fetal renal cystic diseases has
been proposed. 67 Among the nongenetic cystic diseases, multicystic
dysplastic kidney (MCDK) and obstructive dysplasia are
the most common. Genetic diseases include autosomal recessive
and autosomal dominant polycystic kidney disease (ADPKD),
and a growing number of cilia-related disorders (ciliopathies)
associated with cystic kidneys as well as other abnormalities. 68,69
Many of these diseases have been associated with one or several
genetic mutations, and an accurate genetic diagnosis is crucial
for genetic counseling, prenatal diagnosis, and clinical
management.
Multicystic Dysplastic Kidney
MCDK is the most common form of renal cystic disease in
childhood and represents one of the most common abdominal
masses in the neonate. he majority of cases are associated with
an atretic ureter and pelvoinfundibular atresia. he kidney is
replaced by multiple cysts of varying sizes. Between the cysts is
a dense stroma, and there is usually no normal renal parenchyma.
Kidneys afected with multicystic dysplasia are almost always
nonfunctional. hus the prognosis depends entirely on the
function of the contralateral kidney. Multicystic renal dysplasia
usually afects the whole kidney. However, it can be segmental
and can occur in the portion of the duplex kidney supplied by
the atretic ureter.
he sonographic indings correlate with the gross pathologic
appearance. he malformed kidney is usually enlarged but may
be normal in size or small. here are multiple cysts of varying
sizes that do not communicate with one another and are randomly
distributed (Fig. 39.12). Large peripheral cysts distort the reniform
contour. he renal pelvis and ureter are usually atretic and not
visible. On color Doppler evaluation, the renal artery is either
absent or very small. Occasionally an MCDK with a large central
cyst and small peripheral cysts can mimic hydronephrosis from
ureteropelvic junction (UPJ) obstruction (see later discussion).
In hydronephrosis, however, the dilated calyces are of uniform
size and anatomically aligned and communicate with the dilated
renal pelvis. he kidney usually maintains the reniform contour,
with renal parenchyma present peripherally.
he appearance and size of the MCDK may change markedly
during gestation and ater birth (see Fig. 39.12). On serial
examinations, the kidney and its cysts may increase or decrease
in size or may initially enlarge and later involute. 70 his variable
appearance may result from residual renal function and/or
progressive ibrosis.
Assessment of the contralateral kidney is very important. In
19% to 24% of cases, multicystic renal dysplasia is bilateral 71,72
(Fig. 39.13). In unilateral multicystic renal dysplasia, contralateral
renal abnormalities are present in 13% to 26%, including renal
agenesis and UPJ obstruction. 71,73 In fetuses with MCDK, severe
oligohydramnios and nonvisualization of the urinary bladder
imply lethal renal disease, either bilateral MCDK or contralateral
severe renal dysfunction or agenesis. Normal AFV is reassuring.
If there is contralateral hydronephrosis, follow-up ultrasound is
necessary to monitor any progressive dilation or oligohydramnios
that may afect obstetric management. Unilateral MCDK, without
associated renal or nonrenal abnormalities, is associated with a
favorable outcome. 74 A postnatal ultrasound is performed ater
48 hours of age. Prophylactic antibiotic therapy is usually initiated
soon ater birth, pending the results of postnatal ultrasound and
A
B
FIG. 39.12 Unilateral Multicystic Dysplastic Kidney. (A) Image of the fetus at 20 weeks’ gestation demonstrates multiple small cysts in a
slightly enlarged kidney (calipers); B, bladder. (B) Follow-up image at 28 weeks’ gestation demonstrates a greatly enlarged kidney (calipers). Cysts
have increased in size, do not communicate, and are randomly distributed.