WILMS TUMOUR ULTRASOUND DIAGNOSIS

Wilms’ tumour
The most common paediatric renal malignancy, Wilms’ tumour usually presents before the age of 3 years. Although the lesion generally occurs in previously fit individuals, there are several known predisposing conditions, including hemihypertrophy, Beckwith–Wiedemann syndrome and sporadic aniridia, with a 30–40% incidence in sporadic aniridia.

The tumours are large at presentation, presenting with a palpable abdominal mass, and, less frequently, pain, haematuria and fever. About 5% of these tumours are bilateral. The prognosis when unilateral is generally good.

The ultrasound appearances are of a relatively well-defined heterogeneous mass, predominantly solid but frequently with some necrotic or haemorrhagic areas, often almost completely replacing the kidney. Small focal areas of calcification are seen very occasionally. A search should be made for tumour invasion of the renal vein and IVC which occurs in up to 10% of cases. Tumour invasion may extend into the right atrium.

Occasionally a large, right-sided Wilms’ tumour may compress the IVC but not invade it; colour or power Doppler may be useful in the difficult distinction between compression and invasion on ultrasound. Ultrasound also identifies associated lymphadenopathy, particularly in the para-aortic and paracaval regions, and metastatic liver disease. In a small percentage of cases, tumour may also be found in the contralateral kidney. This is usually much smaller than the mass on the presenting side and may be acoustically subtle.

Up to 7% of contralateral tumours are missed on preoperative imaging due to their small size and the operator must be alert to the possibility of bilateral disease. Occasionally a Wilms’ tumour may be found to be predominantly cystic, having the appearances of a large, multiloculated cystic mass. The main differential diagnosis would be of a mesonephric blastoma occurring during the first year of life and histology is required to establish the diagnosis.

In most cases, an ultrasound and chest radiograph are sufficient to diagnose correctly Wilms’ tumour but CT of the chest and abdomen is generally used for staging, and to exclude metastatic disease in the chest and liver. Percutaneous biopsy for confirmation of histological type is generally performed. CT or MRI is more sensitive than ultrasound scanning in demonstrating small tumours in the contralateral kidney.