[An incidental finding of renal cysts: routine occurrence or a finding deserving clarification?]

Since the introduction of new non-invasive diagnostic techniques such as abdominal ultrasound and computerized tomography, simple renal cysts are diagnosed with increasing frequency. Over 30% of patients over 50 years of age are found to have simple renal cysts of different size. A cystic renal mass may represent a simple renal cyst without clinical relevance, a cystic renal carcinoma, early evidence of polycystic kidney disease in a young patient, a rare cause of renal hypertension, a source of infection in a symptomatic patient (infected renal cyst), or a manifestation of an infectious disease (renal abscess, echinococcus cyst). The differential diagnosis and management of a cystic renal mass therefore remain a clinical problem. In the past, surgical exploration of a cystic renal mass was frequently performed. Today, modern diagnostic techniques such as ultrasound-guided percutaneous cyst puncture with cytological analysis of the cyst content, or computerized tomography, are considered the methods of choice. They are particularly useful in case of doubt about the dignity of a cystic renal mass. The determination of renal venous renin levels may be useful in differentiating the causal role of a renal cyst in a patient with hypertension. The management of a cystic renal mass depends on the underlying disease.