Diagnostic ultrasound ( PDFDrive )

CHAPTER 9 The Kidney and Urinary Tract 337
A
B
FIG. 9.38 Twinkle Artifacts Indicating Renal Calculi. (A) Transverse sonogram and simultaneous Doppler image show shadowing calculi,
posterior shadowing, and color Doppler twinkle artifact. (B) A follow-up CT shows the larger calculus. The color Doppler twinkle artifact may
sometimes aid in detection of small calculi, although often no corresponding calculi are shown on noncontrast-enhanced CT. The reason for this
discrepancy is not clear, although it may be due to relatively large (5-mm) collimation typically used for the CT evaluation of calculi.
FIG. 9.39 Sonographic Feature Mimicking Renal Calculus. Transverse
sonogram shows a linear distal renal artery calciication.
Entities That Mimic Renal Calculi
Intrarenal gas
Renal artery calciication
Calciied sloughed papilla
Calciied transitional cell tumor
Alkaline-encrusted pyelitis
Encrusted calciication of ureteric stent
Ureteral Calculi
he search for ureteral calculi may be particularly diicult at
sonography because of overlying bowel gas and the deep retroperitoneal
location of the ureter (Fig. 9.40). However, transvaginal
or transperineal scanning aid in detection of distal ureteral calculi
that are not seen with a transabdominal suprapubic approach. 83,102,103
When the ureter is dilated, the distal 3 cm will be seen as a tubular
hypoechoic structure entering the bladder obliquely. A stone will
be identiied as an echogenic focus with sharp, distal acoustic
shadowing within the ureteric lumen (Fig. 9.41). here may be
associated mucosal edema at the bladder trigone. Transabdominal
evaluation of the ureteral oriices for jets is helpful to assess for
obstruction (Video 9.1). 104 At gray-scale ultrasound, a stream of
low-level echoes can be seen entering the bladder from the ureteral
oriice. he jet is likely shown at ultrasound because of both motion
and a density diference between the jet and urine in the bladder. 105
Good hydration before the study maximizes the density
diference between ureteral and bladder urine and aids in jet
visualization. 106
In addition to gray-scale evaluation, Doppler ultrasound
improves detection of ureteric jets. Color Doppler allows for
simultaneous visualization of both ureteral oriices 104 (Fig. 9.42).
Depending on the state of hydration, jet frequency may vary
from less than one per minute to continuous low; however, jets
should be symmetric in a healthy individual. Patients with highgrade
ureteral obstruction will have either a completely absent
jet or a continuous, low-level jet on the symptomatic side. Patients
with low-grade obstruction may or may not have asymmetric
jets. 104 Semiqualitative assessment of relative jet frequency from
the afected side 107 may improve diagnostic accuracy, but this
technique has not been widely adopted. hus centers that evaluate
ureteral jets with color Doppler use the technique as an adjunct
for assessing ureteric obstruction and the possibility of spontaneous
ureteral stone passage.
Initial studies suggested that the addition of renal duplex
Doppler to the gray-scale ultrasound examination would allow
diagnosis of both acute and chronic urinary tract obstruction. 108
Several studies indicated that the complex hemodynamics that
occur with unrelieved obstruction can be semiquantitatively
assessed by measuring intrarenal arterial resistive indices (RI =