[Atypical cysts and cystic tumours of the kidney: histological, radiological and surgical considerations. Conclusions of the AFU 2007 forum].

Malignant tumours may have a cystic appearance. They are dominated by multilocular cystic renal cell carcinoma, usually low-grade, which rarely metastasize. The Bosniak classification distinguishes non suspicious lesions (type I and II) from suspicious lesions (type III and IV) requiring resection and lesions requiring follow-up (type IIF). The main feature suggestive of malignancy is the enhancement of the septa and the walls of the cyst. Renal cysts classified as IIF require surveillance by contrast-enhanced imaging (CT, MRI or ultrasound). The treatment of cystic tumours is based on surgery. Partial nephrectomy is recommended in this type of tumour regardless of the size. Laparoscopy is a validated technique in experienced hands. Aspiration is not very effective for the treatment of benign cysts, but may be useful for diagnosis. Surgical resection of the roof of the cyst is the most effective technique.