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ABDOMINAL ULTRASOUND
Autosomal recessive (infantile) polycystic
kidney disease (PCKD)
This autosomal recessive condition may often be
diagnosed prenatally on ultrasound. The disease
carries a high mortality rate in early childhood, and
is therefore rarely seen on ultrasound in children.
Tiny cysts replace both kidneys, giving them a
hyperechogenic appearance due to the multiple
reflections from the cyst walls and the overall
increased through-transmission.
Acquired cystic disease
This condition tends to affect patients on long-term
dialysis who may already have shrunken, end-stage
kidneys. Its frequency increases with the duration of
dialysis.
Multiple cysts form in the kidneys, which may,
like adult PCKD, haemorrhage or become infected.
The disease tends to be more severe the longer the
patient has been on dialysis. The proliferative
changes which cause acquired cystic disease also
give rise to small adenomata and the ultrasound
appearances may be a combination of cysts and
solid, hypoechoic nodules. In particular, acquired
cystic disease has the potential for malignancy 3,4
and it is therefore prudent to screen native kidneys,
even after renal transplantation has been performed
(Fig. 7.7).
Figure 7.7 Acquired cystic disease in a patient with
chronic renal failure who has been on long-term dialysis.
Multicystic dysplastic kidney (MCDK)
This is a congenital malformation of the kidney, in
which the renal tissue is completely replaced by
cysts. It is frequently diagnosed prenatally (although
it is naturally a lethal condition if bilateral).
The MCDK may shrink with age and, by adulthood,
may be so small that it is difficult to detect
and may be mistaken for an absent kidney.
Contralateral renal hypertrophy is often present.
MCDK can be associated with contralateral pelviureteric
junction obstruction, which is also frequently
diagnosed in utero.
It is thought that MCDK occurs as a result of
severe early renal obstruction during development
in utero. Obstructed calyces become blocked off,
forming numerous cysts which do not connect.
BENIGN FOCAL RENAL TUMOURS
Angiomyolipoma
This is a homogeneous, highly echogenic, usually
rounded lesion in the renal parenchyma containing
blood vessels, muscle tissue and fat, as the name
suggests. They are usually solitary, asymptomatic
lesions, found incidentally on the scan, although
the larger lesions can haemorrhage, causing
haematuria and pain. Angiomyolipomas are also
associated with tuberose sclerosis, when they are
often multiple and bilateral (Fig. 7.8).
Because the contrast between the hypoechoic
renal parenchyma and the hyperechoic angiomyolipoma
is so great, very small lesions in the order of
a few millimetres can easily be recognized.
It may be difficult confidently to differentiate an
angiomyolipoma from a malignant renal neoplasm,
particularly in a patient with haematuria. Angiomyolipomas
tend to be smaller and more echogenic
than renal cell carcinomas, and sometimes demonstrate
shadowing, which is not normally seen in
small carcinomas. 5 When doubt persists, CT is
often able to differentiate in these cases by identifying
the fat content of the lesion.
Adenoma
The renal adenoma is usually a small, well-defined
hyperechoic lesion, similar in appearance to the