57-year-old woman, personal history of depression, under medical treatment, undergoing surgery for varicose veins.

She was being examined by her primary care doctor for low back pain of 1 year's duration, under medical treatment with NSAIDs. An abdominal ultrasound scan found a mixed cyst (solid and liquid) in the right kidney measuring 7.4 x 4.2 cm in diameter with suspected hydatid cyst.

The patient was referred to our clinic. Examination was unremarkable and laboratory tests, including hydatid cyst serology, were normal.

An abdominal CT scan was requested to complete the study and a tumour was found in the right interpolar and upper polar region with a well-defined outline, internal partitioning and low density of content with a size of 70x45x40mm corresponding to a complex cyst; no regional adenopathies were seen. The characteristics of the cystic tumour do not allow malignancy to be totally ruled out,

A right nephrectomy was performed and anatomopathological study of the specimen revealed a 4.5 cm multiloculated cystic formation with serous content, well defined and lined with flat epithelium, with a diagnosis of multicystic nephroma.