[Cystic nephroma : a rare kidney neoplasm].

Cystic nephroma is a rare kidney neoplasm belonging to the entity of cystic tumours. It is a slow-growing tumour, which develops insidiously, sometimes reaching a considerable size. The diagnosis is more often accidental (except for mass syndrome in children). It is a benign tumour that may be treated by partial sparing nephrectomy. Malignant degeneration is few and far between. However, no medical examination can confirm the diagnosis before surgery. On medical imaging, the tumour enhances after contrast injection and there will always be a doubt about the benignity. Furthermore, percutaneous biopsy of the mass is not contributory to the diagnosis. This means that it is not easy to propose a conservative surgical treatment, even though this remains the best way to deal with such a tumour.