Fig. 5.1
Longitudinal US scanning of the kidney shows a calcific stone, which appears as bright echogenic foci with posterior acoustic shadowing. No dilatation of collecting system is present
Fig. 5.2
Staghorn stone: renal pelvic stones may grow to large size by occupying completely the pelvic space and forming a cast of the renal pelvis and calices. They are usually associated with chronic urinary tract infections. Staghorn stone usually appears as a densely calcified mass, producing marked posterior acoustic shadowing
Fig. 5.3
Twinkle artifact appears as a tail linear band of alternating colors behind the stone
Stones can be easily visualized if they are in the kidneys and the distal ureter at or near the ureterovesical junction, especially if dilatation is present (Fig. 5.4), while small stones (<5 mm) or stones within the ureter cannot be detected with US. Sometimes the ureterovesical junction is not easy to be visualized: in these cases, a urine-filled bladder is mandatory and provides an excellent acoustic window for US. Even if US remains less accurate than IVU or CT in the assessment of this region, color Doppler examination can provide useful additional information as the presence or absence of ureteral jet. The pumping effects of calyceal peristalsis and the renal diuresis that lead to protrusion of urine into the bladder. On color Doppler it appears as a colored jet near the ureterovesical junction. In normal conditions, deep breath and Valsalva maneuver lead to a bilateral ureteral jet (Fig. 5.5). The unilateral absence of ureteral jet on the symptomatic side in a well-hydrated patient is pathognomonic of complete obstruction, while asymmetry of ureteral jets is suggestive of incomplete obstruction [4].
Fig. 5.4
Obstructive calculus within the distal ureter, near the ureterovesical junction. The stone provides complete obstruction and dilatation of the distal tract of the ureter
Fig. 5.5
Normal ureteral jet. The arrival of urine into the bladder appears as a turbulence of the flow near the ureterovesical junction. Color Doppler confirms the presence of a high-velocity flow
Diagnostic criteria of obstructive urolithiasis include direct visualization of the stone and dilatation of ureter more than 6 mm in diameter.
The dilatation of renal collecting system is scored from grade 1 to 3, which means a minimal, moderate, or severe calyceal dilatation with thinning of the renal cortex (Fig. 5.6).
