saline groups for the median volume of the simple renal cysts (165 [52 480] vs. 178 [42 520] cm3, respectively, p = 0.995). Figure 3 displays the number of patients in the ethanol and hypertonic saline groups with complete and partial regression, and those with failure at the follow-up six months after sclerotherapy. The number of patients of the ethanol and hypertonic saline groups with complete regres- sion were 34 and 26, respectively. The complete regression ratio of the ethanol group was significantly higher (94% vs. 72%, respectively) than that of the hypertonic saline group (p = 0.024). There was one patient each with partial regression in both the ethanol and hypertonic saline groups. The partial regression ratios of the ethanol and hypertonic saline groups were similar (3% vs. 3%, respec- tively). The number of failures of the ethanol and hypertonic saline groups was one and nine, respectively. The failure ratio of the ethanol group was significantly lower (3% vs. 25%, respectively) than that of the hypertonic saline group (p = 0.014). Fig. 3. The number of patients, with complete and partial regres- sion and failure at six months follow-up after sclerotherapy, in the ethanol and hypertonic saline groups. Their percentages are also presented. aP = 0.024 vs. the complete regression ratio of the hypertonic saline group with using Fisher’s exact test. bP = 0.014 vs. the failure ratio of the hypertonic saline group with using Fisher’s exact test. 516 Egilmez et al. After failure of the sclerotherapy, the procedure was repeated with the same sclerosant because of persistent flank pain. The procedure was repeated one more time in one patient in the ethanol group and one more time in five patient, two more times in two patient and three more times in two patient in the hypertonic saline group. At the end of the study, the flank pain was controlled in all the patients with repeated sclerotherapies. Complete regres- sion was obtained for the repeatedly treated patient in the ethanol group and for the seven repeatedly treated patients in the hypertonic saline group. Partial regression was obtained in two of the nine patients who required repeated sclerotherapy in the hypertonic saline group. There were no other serious complications after therapy in the study groups. During the sclerotheraphy, ten patients in the ethanol group developed mild flank pain that required medical management with an oral nonsteroidal anti-inflammatory drug during the filling of the cystic cavity with the sclerosant. There was no pain during the filling of sclerosant in the hypertonic saline group. DISCUSSION Simple renal cysts are by definition unilocular, they do not communicate with the collecting system, they occur in a kidney that is otherwise normal and they have an epithe- lial lining that contains no renal elements. The vast majority of simple cysts encountered in clinical practice develop in otherwise normal kidneys and these cysts are now considered to be acquired lesion, and the age- dependence of cysts has been detected in several studies as evidence in favor of this concept (26). These occur as multiple or single, usually cortical, cystic spaces that vary widely in diameter. They are commonly 1 to 5 cm, but they may reach 10 cm or more in size. Although the vast majority of simple renal cysts are entirely asymptomatic and do not require any treatment, intervention is needed when they are symptomatic and cause obstruction of the urinary tract. Simple renal cyst that develop adjacent to the renal hilum can cause flank pain, abdominal pain, hematuria, recurrent urinary infections, hypertension, polycythemia and/or obstructive uropathy (6, 27). Spontaneous, iatrogenic or traumatic rupture of a large renal cyst will also cause hematuria or pain. The first line of therapy for pain secondary to benign renal cysts is medical management with nonsteroidal anti- inflammatory agents or narcotics. When this therapy is insufficient or other symptoms occur, then decompression may be indicated. The treatment options include percuta- neous aspiration with or without sclerosis, percutaneous Korean J Radiol 8(6), December 2007