A 9-year-old girl was admitted to the paediatric department from the emergency department for the second episode of macroscopic haematuria in 20 days.

No family history of interest, personal history of facial haemihypertrophy due to congenital torticollis, chickenpox, infectious mononucleosis, nocturnal enuresis until the age of 7, pneumonia at 9 months and trauma to the coccyx.

Physical examination: slight skin pallor, weight within the 25-50 percentile and height within the 50-75 percentile. No other findings.

Complementary examinations: complete blood count, biochemistry, coagulation, urine culture, renal function, enolase, alpha-fetoprotein, chest X-ray and ECG were normal.

Urinary sediment: macroscopic haematuria.

Abdominal ultrasound: 5cm diameter mass in the left kidney, complex with cystic/necrotic areas.

The paediatrics department consulted our department and decided to perform an abdominal CT scan with contrast after ultrasound findings, with the finding of a mass depending on the left kidney, in the anterior face, with cystic content and irregular endoluminal thickening. It presents a thick and irregular septum of similar density to that obtained in the internal irregularities described. No inter-cavo-aortic or periaortic adenomegaly was observed.

The mass is compatible with Wilms' tumour or adeno-carcinoma.

It was decided to perform a left nephrectomy: the mass measured 4.5 cm in diameter.

The anatomopathological diagnosis was cystic mesoblastic nephroma (multilocular renal cyst).