9%20ECOGRAFIA%20ABDOMINAL%20COMO%20CUANDO%20DONDE

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ABDOMINAL ULTRASOUND
b
A
B
Figure 9.7 (A) Pelvic kidney (b = bladder). (B) Dimercaptosuccinic acid (DMSA) scintigraphy shows 33% function in
the smaller, pelvic RK and 66% in the left kidney (LK).
Renal agenesis
The kidneys form from the ureteric bud, which
arises from the pelvic area during the fifth to sixth
week of gestation. The bud undergoes numerous
divisions, forming the ureters, renal pelvis, calyces
and renal tubules. Any interruption of this process
may cause renal agenesis or ectopia.
Bilateral renal agenesis is lethal and is usually
diagnosed prenatally. The incidence of unilateral
renal agenesis is about 1:450 live births and is usually
prenatally detected. Ultrasound is useful in
confirming the prenatal diagnosis and excluding
the presence of an ectopic kidney. A DMSA scan
confirms the diagnosis. Renal agenesis is associated
with VATER syndrome and with ipsilateral gynaecological
anomalies in girls.
Multicystic dysplastic kidney (MCDK)
The MCDK is generally the result of complete,
early ureteric obstruction in utero before 10 weeks,
and is frequently diagnosed antenatally. The resulting
kidney is non-functioning and contains cysts of
varying sizes, separated by echogenic ‘dysplastic’
renal parenchyma. In general the cysts do not communicate
but occasionally some communication
can be seen, making differentiation from a severe
hydronephrosis difficult.
MCDK is usually unilateral and is considered a
benign condition, although there is a slight risk of
malignancy and hypertension in later life. The kidney
gradually involutes and often completely disappears
(Fig. 9.8A, B). Surgical removal is
unnecessary unless symptomatic due to its large
size or is associated with repeated episodes of infection.
Provided the contralateral kidney is normal,
with good function, the prognosis is good. There
is, however, an increased risk of associated urinary
tract anomalies, such as ureterocoele, vesicoureteric
reflux or contralateral pelviureteric junction
obstruction, which may predispose to
infection. These can be demonstrated with ultrasound
and micturating cysto-urethrogram.
A DMSA scan differentiates MCDK, which is
completely non-functioning, from a grossly
hydronephrotic kidney, a distinction which may
sometimes be difficult to make on ultrasound.
Follow-up ultrasound scanning is generally advised
in view of the slight increased risk of Wilms’
tumour and to monitor the growth of the contralateral
kidney.
Polycystic disease of the kidneys
Autosomal recessive polycystic disease of the kidney
(ARPCDK: infantile) may be diagnosed prenatally.
Both kidneys are abnormal, being large and
hyperechoic, with loss of corticomedullary differentiation
(Fig. 9.8C). There is a spectrum of severity
of disease and in some cases it may present later