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THE RENAL TRACT 173
Ultrasound still has a major role, however, not
just in calculus detection but in identifying the
secondary effects, that is, hydronephrosis, and
where necessary, guiding renal drainage. The PCS
may be obstructed proximal to the stone. Obvious
hydronephrosis may be present and a dilated ureter
may be apparent when the stone has travelled distally.
The stone can sometimes be identified in the
dilated ureter, but this is unusual as the retroperitoneum
is frequently obscured by overlying bowel.
Plain X-ray and/or IVU are traditional essential
adjuncts to investigating renal colic in these cases;
however CT IVU is rapidly becoming accepted as
one of the mainstream investigations. 17
Early obstruction occurs before the PCS can
become dilated, making the diagnosis more difficult
on ultrasound. Occasionally there will be mild
separation of the PCS to give a clue, but sometimes
the kidney appears normal. Doppler ultrasound
can help to diagnose obstruction in a non-dilated
kidney, as discussed previously; however this may
not always be definitive.
Staghorn calculi
These large calculi are so called because they occupy
a significant proportion of the collecting system,
giving the appearance of a staghorn on X-ray (Fig.
7.16B). They may be less obvious on ultrasound
than on X-ray, casting a dense shadow from the PCS
which may obscure any associated dilatation and
can, in small, atrophied kidneys, be misinterpreted
as shadowing from bowel gas. Because of the lobulated
shape of the calculus it may appear as several
separate calculi on ultrasound. A coronal section
may therefore be more successful in confirming a
staghorn calculus than a sagittal section.
Cystinuria
This rare metabolic disease causes crystals of cystine
to precipitate in the kidneys and be excreted in
the urine (Fig. 7.17). Cystine stones form in the
kidneys and may result in obstruction.
Nephrocalcinosis
This term is used to describe the deposition of calcium
in the renal parenchyma. It is most often
RK TRV
Figure 7.17 Cystinuria. TS through the RK. Small,
highly reflective crystals of cystine are demonstrated.
related to the medullary pyramids and is frequently
associated with medullary sponge kidney (see
below). It may also be seen in papillary necrosis
and in patients with disorders of calcium metabolism,
e.g. hyperparathyroidism.
Ultrasound appearances
Nephrocalcinosis may affect some or all of the pyramids.
A regular arrangement of hyperechoic pyramids
are seen which may shadow if large calcific
foci are present, but not if the foci are numerous
and tiny, as they are smaller than the beam width
(Fig. 7.18).
Less frequently, calcification is seen in the renal
cortex.
Hyperparathyroidism
The (normally) four parathyroid glands in the neck
regulate calcium metabolism in the body. Patients
with primary hyperparathyroidism (due to an adenoma
or hyperplasia of one or more of the parathyroid
glands) have hypercalcaemia, which makes
them prone to nephrocalcinosis or stones in the
kidneys.
Secondary hyperparathyroidism is associated
with chronic renal failure; hypocalcaemia, which
results from the chronic renal failure, induces