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170
ABDOMINAL ULTRASOUND
can be observed when the obstruction has been
relieved or after the renal PCS has become dilated.
This effect often does not persist once the
kidney dilates, presumably because the intrarenal
pressure is relieved, which emphasizes the use
of Doppler in acute cases, before dilatation has
become established. 14 Because of the vagaries
of the stage of obstruction, renal pressure, etc.
the interpretation of RI should be made cautiously.
IVU will show delayed PCS opacification and is
also more useful than ultrasound in assessing the
level of obstruction. CT IVU, as mentioned previously,
is more commonly fulfilling the role previously
held by the IVU.
Vesicoureteric junction
The normal ureters may be identified on ultrasound
with high-resolution equipment, as they enter the
bladder. Jets of urine emerge into the bladder at
these points and can be demonstrated with colour
Doppler. An absent or reduced number of jets may
indicate obstruction on that side; this finding again
should be interpreted cautiously. Ureteric jet
analysis is not routinely performed at most hospitals
as a diagnostic test of renal obstruction.
Careful scanning at the VUJs can identify significant
anomalies (Figs 7.12 D, E):
●
●
●
Reflux can be seen to dilate the ureter
intermittently (see below).
A ureterocoele may be diagnosed as it dilates with
the passage of urine; it may not be obvious until
the operator has watched carefully for a few
minutes.
Stones may become lodged at the VUJ,
causing proximal dilatation.
Non-obstructive hydronephrosis
Not all renal dilatation is the result of an obstructive
process and the kidney may frequently be
dilated for other reasons.
Reflux
This is the most common cause of non-obstructive
renal dilatation, and is normally diagnosed in children.
Reflux is associated with recurrent urinary
tract infections and can result in reflux nephropathy,
in which the renal parenchyma is irretrievably
damaged.
Reflux can be distinguished from other causes of
renal dilatation by observing the dilatation of the
ureters at the bladder base, due to the retrograde
passage of urine. For a more detailed consideration
of the diagnosis of reflux, see Chapter 9.
Postobstructive dilatation
Dilatation of a once severely obstructed kidney
may persist. The PCS remains baggy and dilated
despite the obstruction having been relieved.
Papillary necrosis
The renal papillae, which are situated in the medulla
adjacent to the calyces, are susceptible to ischaemia
due to relatively low oxygenation in the region of
the medullary junction. This is particularly associated
with diabetic patients and those on long-term
anti-inflammatory or analgesic medication.
The papillae tend to necrose and slough off,
causing blunting of calyces on IVU. Sloughed-off
papillae may lodge in the entrance to the calyces,
causing obstruction.
Papillary necrosis is difficult to detect on ultrasound
unless advanced. It appears as prominent
calyces with increased corticomedullary differentiation.
IVU is the imaging method of choice (Fig.
7.15).
Congenital megacalyces
This is a congenital condition in which the PCS is
dilated due to poor development of the papillae.
The calyces are normally markedly enlarged but
the cortex is normal and the ureters are of normal
calibre and not dilated. 15 Occasionally this is associated
with congenital megaureter in which the
muscular layer of the ureter is atonic.
Differential diagnoses for fluid-filled renal
masses are summarized in Table 7.2.
RENAL TRACT CALCIFICATON
Calcification within the kidney usually occurs in
the form of stones. Smaller foci of calcium, which
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