Diagnostic ultrasound ( PDFDrive )

CHAPTER 52 The Pediatric Urinary Tract and Adrenal Glands 1783
central echo complex is much less prominent compared with
the renal parenchyma because there is less peripelvic fat in the
infant than in the adult. Renal cortical echogenicity is typically
increased in the normal premature infant kidney compared
with the liver and spleen. he echogenicity of the renal cortex
in the normal term infant kidney is oten the same as the
echogenicity of the adjacent normal liver, whereas in the older
child and adult kidney, the renal cortex is less echogenic than
the liver. he medullary pyramids in the infant are relatively
larger and tend to appear more prominent (more hypoechoic).
he corticomedullary diferentiation is greater in the infant and
child’s kidney than in the adult, possibly because of increased
resolution from higher frequency transducers and less overlying
body fat tissue. It may also result from diferences in the cellular
composition of the renal parenchyma in the infant. hese
prominent pyramids in the pediatric kidney can easily be mistaken
for multiple cysts or dilated calyces by those not familiar with
the diferences. Normal pyramids line up around the central
echo complex in a characteristic pattern and can therefore be
diferentiated from cysts. he position of the arcuate artery at
the corticomedullary junction can also help to identify a structure
as a pyramid.
Renal anatomy in the teenager and older child is similar to that
in the adult 5,21,22 (see Fig. 52.8). he renal parenchyma consists
of the cortex, which is peripheral, contains the glomeruli, and
has several extensions to the edge of the renal sinus (the septa
or column of Bertin); and the medulla (containing the renal
pyramids), which is more central and adjacent to the calyces.
he normal cortex produces low-level, backscattered echoes.
he medullary pyramids are relatively hypoechoic and arranged
around the central, echo-producing renal sinus. he arcuate
vessels can be demonstrated as intense specular echoes at the
corticomedullary junction. his corticomedullary diferentiation
can be identiied in most children but occasionally cannot be
visualized in those with increased overlying sot tissues. he
central echo complex consists of strong specular echoes from
the renal sinus, including the renal collecting system, calyces
and infundibula, arteries, veins, lymphatics, peripelvic fat, and
part of the renal pelvis. With distention of the renal collecting
system, these echoes become separated and small degrees of
hydronephrosis can be demonstrated. Mild degrees of distention
can be seen in normal children, particularly ater recent
high intake of luids or diuretics. A normally distended urinary
bladder can also cause functional ureteral obstruction and mild
distention of the renal collecting systems. Rescanning when the
bladder is empty will usually result in resolution of both collecting
system and ureteral distention in an otherwise normal
urinary tract.
Normal Bladder Anatomy
he normal urinary bladder is thin walled. Bladder volume and
wall thickness are inluenced by the degree of bladder distention.
15,16 he distal ureters may be visible at the bladder base,
especially if the child is well hydrated, likely related to the normal
transient passage of urine associated with peristalsis (Fig. 52.9).
Bladder wall thickness may increase with inlammation or
muscular hypertrophy.
FIG. 52.9 Normal Distal Ureters. Transverse bladder image depicts
distal ureteral insertions at the level of the trigone (arrows).
CONGENITAL ANOMALIES OF THE
URINARY TRACT
Renal Duplication
A common congenital anomaly of the urinary tract is duplication
of the collecting system, which may be partial or complete. In
complete duplication, two pelves and two separate ureters drain
the kidney. he lower-pole ureter usually inserts into the bladder
at the normal site. However, the intramural portion of the ureter
may be shorter than usual, and vesicoureteral relux (VUR)
frequently results. 23 he upper-pole ureter oten inserts ectopically,
inferior and medial to the site of the normal ureteral insertion
(Weigert-Meyer rule). Its oriice may be stenotic and obstructed.
Ballooning of the submucosal portion of this upper-pole ureter
causes a ureterocele. In some patients, the upper-pole ureter
may have an insertion entirely outside the bladder including the
urethra (above, at, or below the external urinary sphincter), in
the uterus or vagina, or in the ejaculatory duct, seminal vesicle,
or vas deferens. 24
Patients with unobstructed duplications have no more clinical
problems than their normal counterparts. Patients with complicated
renal duplications may have UTI, failure to thrive, abdominal
mass, hematuria, or symptoms of bladder outlet obstruction from
a ureterocele. Female patients with urethral insertion of the
upper-pole ureter below the external urinary sphincter or with
vaginal or uterine insertion may have chronic, constant urinary
incontinence or frequent dribbling.
Duplication of the renal collecting system is diagnosed on
sonography when the central echo complex separates into two
parts with an interposed column of normal renal parenchyma
(column of Bertin) (Fig. 52.10). Unless collecting system dilation
and/or ureteral dilation are present, it is usually impossible to
distinguish a partial, uncomplicated duplication from a complete
duplication because a normal ureter is diicult to visualize
sonographically. 25