Diagnostic ultrasound ( PDFDrive )

318 PART II Abdominal and Pelvic Sonography
with contralateral nephrectomy, renal agenesis, renal hypoplasia,
renal atrophy, and renal dysplasia. Difuse compensatory
hypertrophy is suggested at ultrasound when an enlarged but
otherwise normal-appearing kidney is identiied. he focal form
is seen when residual islands of normal tissue enlarge in an
otherwise diseased kidney; focal compensatory hypertrophy may
be particularly prominent in the setting of relux nephropathy.
Large areas of nodular but normal renal tissue identiied between
scars may mimic a solid renal mass. 5
Anomalies Related to Ascent of Kidney
Ectopia
Failure of the kidney to ascend during embryologic development
results in a pelvic kidney; prevalence is 1 in 724 pediatric
autopsies. 16 hese kidneys are oten small and abnormally rotated.
Fity percent of pelvic kidneys have decreased function. 16 he
ureters are oten short; poor drainage and collecting system
dilatation predispose pelvic kidneys to infection and stone formation.
he blood supply is oten complex; multiple arteries may
be derived from regional arteries (typically, internal iliac or
common iliac). If the kidney ascends too high, it may pass through
the foramen of Bochdalek and become a true thoracic kidney;
this is usually of no clinical signiicance. A search for a pelvic
kidney should be performed if the kidney is not identiied within
renal fossae (Fig. 9.9). If the kidney has ascended too high,
ultrasound is helpful to determine if the diaphragm is intact.
Crossed Renal Ectopia
In crossed renal ectopia, both kidneys are found on the same
side. In 85% to 90% of cases, the ectopic kidney will be fused
to the other kidney (crossed-fused ectopia). he upper pole of
the ectopic kidney is usually fused to the lower pole of the other
kidney, although fusion may occur anywhere. he incidence is
1 in 1000 to 1 in 1500 at autopsy. 15 Fusion of metanephrogenic
blastema does not allow proper rotation or ascent; thus both
kidneys are more caudally located, although the ureterovesical
junctions (UVJs) are located normally. At sonography, both
kidneys are on the same side and are typically fused (Fig. 9.10).
In patients with renal colic, knowing that the UVJs are in the
normal location is particularly important, since bilateral ureters
need to be assessed.
Horseshoe Kidney
he incidence of horseshoe kidneys in the general population
is 0.01% to 0.25%. Horseshoe kidneys occur when metanephrogenic
blastema fuse prior to ascent; fusion is usually at the
lower poles (95%). Typically, the isthmus is composed of functioning
renal tissue, although rarely it is made up of ibrous tissue.
he horseshoe kidney sits anterior to the abdominal great vessels
and derives its blood supply from the aorta and other regional
vessels, such as inferior mesenteric, common iliac, internal iliac,
and external iliac arteries. Abnormal rotation of renal pelves
oten results in ureteropelvic junction (UPJ) obstruction; the
horseshoe kidney is thus predisposed to infection and stone
formation. Additional associated anomalies include vesicoureteral
relux, collecting system duplication, renal dysplasia, retrocaval
ureter, supernumerary kidney, anorectal malformation,
esophageal atresia, rectovaginal istula, omphalocele, and
cardiovascular and skeletal abnormalities.
At sonography, horseshoe kidneys are usually lower than
normal and the lower poles project medially. Transverse imaging
of the retroperitoneum will demonstrate the renal isthmus crossing
the midline anterior to abdominal great vessels (Fig. 9.11).
Hydronephrosis (pyelocaliectasis) and collecting system calculi
may be evident.
Anomalies Related to Ureteral Bud
Renal Agenesis
Renal agenesis may be unilateral or bilateral. Bilateral renal
agenesis is a rare anomaly that is incompatible with life. he
prevalence rate of bilateral agenesis at autopsies is 0.04%. he
condition has a 3 : 1 male predominance. 15 Unilateral renal
*
FIG. 9.9 Pelvic Kidney. Transverse sonogram demonstrates a left
pelvic kidney posterior to the uterus (*).
FIG. 9.10 Cross-Fused Ectopia. Sagittal sonogram demonstrates
two kidneys fused to each other.