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ABDOMINAL ULTRASOUND
Ultrasound appearances
Most renal calculi are calcified foci located in the
collecting system of the kidney. Careful scanning
with modern equipment can identify over 90% of
these. 16 Most stones are highly reflective structures
which display distal shadowing (Fig. 7.16). The
shadowing may, however, be difficult to demonstrate
due to the proximity of hyperechoic sinus
echoes distal to the stone, or due to the relatively
small size of the stone compared to the beam
width.
The identification of reflective foci in the kidney
is complicated by the fact that the normal renal
sinus echoes are of similar echogenicity. This
means that small stones may be missed on ultrasound.
Differentiation of stones from sinus fat and
reflective vessel walls is dependent upon careful
technique and optimal use of the equipment. The
operator must adjust the technique to display the
distal shadow by using a variety of scanning angles
and approaches and by ensuring that the suspected
stone lies within the (narrowest) focal zone of the
beam. The higher the frequency used, the better
the chances of identifying the stone.
Clearly the identification of large calculi is normally
straightforward; however, for many of the
reasons above, identification of small calculi can be
difficult, especially in a patient with pain. Both
false-positive and false-negative studies are well
recognized. Although traditionally the plain film,
that is kidneys, ureters, bladder (KUB), is often the
first-line investigation for patients with suspected
calculi, it is now being accepted that CT IVU is the
best and most reliable diagnostic test for calculi
detection (Fig. 7.16 C and D).
RT KIDNEY
A
B
C
Figure 7.16 (A) A calculus within the PCS of the RK. Distal acoustic shadowing is easily seen. (B) A staghorn calculus
fills the entire PCS of the kidney. A sagittal section through the lateral aspect of the kidney gives the impression of
several separate stones, although this is, in fact, a single calculus. (C) CT IVU through the renal area. The right renal
pelvis is mildly dilated (arrow) and a small amount of perirenal stranding is noted, suggestive of obstruction
(arrowheads). (D) CT scan through the bladder showing a small calculus on the right (arrow) at the right vesicoureteric
junction.
D