CT-Guided Sclerotherapy for Simple Renal Cysts Using 95% Ethanol and 20% Hypertonic Saline resection and fulguration or marsupialization, uretero- scopic cyst marsupialization, laparoscopic or retroperito- neoscopic resection, or open surgical resection (28). Should medical management fail for symptomatic peripheral renal cysts, then aspiration and sclerotherapy are preferred as the initial therapy unless these procedures are contraindi- cated by the cyst size or complexity due to the risk of obstructing the collecting system (29). With modern imaging methods, most renal cysts are aspirated as part of the therapeutic process in symptomatic patients. To improve the efficacy, several sclerosant agents are currently used to injure the cyst wall cells, which are responsible for the fluid dynamics of the cyst (6). The inflammation induced by the sclerosant leads to adhesion of the walls and reduction or resolution of the renal cyst. Ethanol is the most widely used among the available sclerosant agents (7, 8, 13). Ethanol might destroy the epithelial wall of the cyst without damaging the adjacent renal parenchyma because its penetration through the fibrous capsule only occurs after 4 12 hr (30). There are published studies related to the successful use of hypertonic saline sclerotherapy in patients with hydatid liver cysts as a primary treatment (31, 32). Kabaalioglu et al. (33) reported a case of 6-year-old girl with a sympto- matic renal cyst, and she underwent successful percuta- neous aspiration and sclerotherapy with hypertonic saline under US guidance. They suggested that US- or CT-guided percutaneous sclerotherapy should always be considered before surgery. Ethanol sclerotherapy has been reported to be successful via performing multi-session treatment with placement of a pigtail catheter inside the cyst for repeated instillation and removal of the alcohol (10). Chung et al. (8) reported that multiple sessions of sclerotherapy are better than a single injection of sclerosant for reducing the recurrence of simple renal cysts. Falci-Junior et al. (12) suggested that the complete disappearance of the cyst might take as long as six months; therefore, an abdominal US examination that revealed the residual cyst during this period did not signify failure or recurrence. They also reported that six months after single-session sclerotherapy, the procedure might be safely repeated to treat any symptomatic cyst that has recurred. Akinci et al. (14) assessed the efficacy and long- term results of single-session ethanol sclerotherapy for treating simple renal cysts. They performed the sclerother- apy procedures with the guidance via fluoroscopy and US for 98 simple renal cysts. In that study, the average reduction of the cyst volume was 93% at the end of the first year and the cysts disappeared completely in 17 (17.5%) patients. After the procedure, improvement of the flank pain was noted in 67 (90%) patients. Sixty-one Korean J Radiol 8(6), December 2007 (82%) patients were free of pain and the pain decreased in six (8%) of them. Second intervention was required in two patients (2%) due to recurrence of cysts and the related symptoms. One (1%) patient had a small retroperitoneal hematoma that resolved spontaneously and in another patient (1%), spontaneous hemorrhage was detected in the cyst one year after the procedure. In this study, single-session percutaneous sclerotherapy was preferred since it was a good option for treating symptomatic renal cysts and it was a highly effective procedure that offered the benefits of a less-invasive approach. Multi-session sclerotherapy is a more time consuming procedure than single-session sclerotherapy; therefore, its morbidity rate may be high because of repeated procedures (13). CT and US are alternative image-guidance systems that are used during percutaneous sclerotherapy for simple renal cyst. We preferred CT- guidance during sclerotherapy because of its advantages for determining the presence of a communication between the simple renal cyst and the pelvicalyceal collecting system after filling the cyst with contrast medium, for exclusion of any leakage from the puncture site into the retroperitoneal cavity and for determining the presence of extravasation. Okeke et al. (6) reported that laparoscopic de-roofing of the cyst is a more effective treatment than single-session sclerotherapy when a symptomatic cyst is established and when definitive treatment of a cyst is indicated. On the long term follow up (mean: 17 months, range: 12 23 months), pain recurred in all five patients who presented with pain and who also underwent sclerotherapy. The high recurrence rate for sclerotherapy might be due to the lower ethanol volume, which was a maximum of 75 ml and 20% of the cyst volume. Lin et al. (34) compared the therapeutic results of the 2- and 4-hr retention techniques during ethanol sclerotherapy with a single-session single- injection technique for treating simple renal cysts. In that study after complete aspiration of the cystic fluid, 95% ethanol was injected into the cyst and it was retained for 4 hr in 14 cysts and for 2 hr in 22 cysts. They found that the average maximal diameter and aspirated volume of the cysts were 8.3 cm and 223 ml in the 2-hr retention group and 7.9 cm and 167 ml in the 4-hr retention group, respec- tively. They regularly followed up the patients by perform- ing US, CT or both at 3-month to 6-month intervals for at least one year. They concluded that the single-session, prolonged ethanol-retention technique is safe and effica- cious for the treatment of renal cysts and there was no difference in therapeutic efficacy between the 2- and 4-hr ethanol-retention techniques. Gasparini et al. (16) evaluated the efficacy of pure 517