[Hyperdense renal cyst].
OBJECTIVE: We update the diagnostic criteria for renal cystic masses, emphasising in the clinical entity known as hyperdense renal cyst. METHODS: We report the case of a male patient who presented with an atypical left renal cyst. Radiological examinations (US and CT) were performed. A description of renal cyst classification is made. We review the diagnostic criteria for hyperdense renal cyst using the iconography from this case and also its therapeutic approach. RESULTS: An image compatible with left simple renal cyst was found on ultrasound. A CT scan study showed an homogeneous mass with a high attenuation value, non vascular in nature, which complies with all diagnostic criteria for hyperdense renal cyst. CONCLUSIONS: Hyperdense renal cyst is a simple cyst which has suffered bleeding or infection. Diagnosis is made by CT scan and it does not require treatment.