The aim of this study was to show additional diagnostic criteria of computed tomography (CT) scan to diagnose and predict the detection and recurrence of cystic renal cell carcinoma in the patients with complicated renal cysts. Furthermore, we would demonstrate the relationship between complicated renal cysts diagnosed by Bosniak system and some parameters of pathological results. The analysis about detection time of renal malignancy would help determine the practical guidelines of follow-up plan for complicated renal cysts.

Even though there have been many trials and errors to enhance the diagnostic accuracy of CT scans for complicated cysts, the trial to obtain the enhanced accuracy using CT scan would be still valuable, when we consider its widespread use. A previous study demonstrated that the enhancement of HU with intravenous administration of contrast material on CT scan by 15 HU would be "almost always indicative of a pathologic process although not always a malignancy", another study showed the cut-off as 42 or 47 HU gap would be helpful in the prediction of renal malignancy.

Inclusion Criteria:

• All patients who were diagnosed as renal cysts
• available serial follow-up data of CT scan
• all CT imaging included non-enhanced (NEP), corticomedullary (CMP), and early excretory phase (EEP) scans. The scan delay times should range from 30 to 40 seconds for CMP scans and from 120 to 180 seconds for EEP scans.

Exclusion Criteria:

• cases diagnosed by only US/MR
• no serial CT images
• cysts of autosomal dominant adult polycystic kidney disease
• cysts less than 1cm in diameter (difficult to evaluate accurately)
• follow-up period less than 1 yr in the patients who had no surgery

All 2,992 patients who were diagnosed as renal cysts in this institute