Diagnostic ultrasound ( PDFDrive )

1784 PART V Pediatric Sonography
With obstruction of an upper-pole moiety, dilation of the
upper-pole collecting system and its entire ureter is seen. he
renal parenchyma may be thinned over the upper-pole collecting
system. If the obstruction is associated with a ureterocele, views
of the bladder may demonstrate the ureterocele as a rounded,
anechoic structure within the bladder in addition to the dilated
distal ureter adjacent to the bladder (Fig. 52.11). A large ureterocele
may cross the midline and obstruct the contralateral
ureter or bladder outlet and cause bilateral hydronephrosis.
Ureteroceles can be diicult to diagnose if they are large enough
to mimic the bladder. If this is a concern, a postvoid scan will
be diagnostic. With relux into the lower-pole moiety, the lowerpole
collecting system and its ureter will be dilated to a varying
degree. If relux is mild, there may be no lower-pole dilation.
Other Renal Anomalies
Other renal anomalies include congenital absence of the kidney,
abnormal position of the kidney (e.g., pelvic kidney, crossed
ectopia), and horseshoe kidney with fusion of the lower poles
in the midline. 26 Congenital absence of the kidney or ectopia
of the kidney is suspected when no renal tissue can be identiied
in the renal fossa on sonography. At birth, the adrenal gland
will not present as the usual inverted V above the kidney but
assumes a lat shape oten called a “lying-down adrenal” (Fig.
52.12). Care must be taken to search for the kidney not only in
its usual location in the renal fossa, but also in the lower abdomen
or pelvis. he contralateral kidney, when healthy, shows compensatory
hypertrophy when one kidney is absent or severely damaged.
Nuclear scintigraphy may be helpful in identifying a small,
functioning kidney not visualized by ultrasound.
With a horseshoe kidney the longitudinal axis of the kidneys
is abnormal. he lower poles are rotated medially and will be
fused in the midline anterior to the spine by a ibrous band or
renal parenchyma (Fig. 52.13). he kidney is also positioned
somewhat lower than usual. A horseshoe kidney can be overlooked
if the abnormal renal axes are not recognized. he central fused
renal tissue may also be thin and easily missed, particularly if
it solely ibrous in nature.
Crossed renal ectopia is a rare congenital anomaly wherein
both kidneys are located on the same side of the abdomen. here
is at least some degree of fusion in approximately 90% of cases,
with the usual pattern consisting of fusion of the orthotopic
FIG. 52.10 Renal Duplication. Longitudinal prone image of the right
kidney demonstrates normal renal parenchyma, a column of Bertin (B)
dividing the central echo complex into two parts (arrows).
FIG. 52.12 “Lying Down” Adrenal Sign in a Neonate With Absence
of the Left Kidney. Longitudinal image depicts an elongated and lattened
adrenal gland (arrows) along the spine. *, Spleen.
A B C
FIG. 52.11 Renal Duplication With Ectopic Ureterocele of Upper-Pole Moiety. (A) Longitudinal image of left kidney reveals dilation of the
upper-pole collecting system (*) and less dilated lower-pole renal pelvis. (B) Longitudinal image of left lank depicts dilated upper-pole ureter (arrow)
extending from renal pelvis. (C) Transverse bladder image shows ureterocele within the bladder (arrow).