Flexible ureteroscope with ultrasound guidance for treatment of parapelvic renal cysts: A complementary approach to locate the cystic wall

The main treatment of parapelvic cysts is exible ureteroscope currently. Considering the intraoperative localization of the cyst may fail with exible ureteroscope, we tend to use an innovative method by ultrasound-guided for easily locating cystic wall during exible ureteroscopic surgery We retrospectively reviewed 17 consecutive cases of parapelvic renal cysts treated by ultrasound-guided exible ureteroscope between March 2017 and May 2020. The differences of simple exible ureteroscopic technique and ultrasound-guided exible ureteroscopic technique were compared. The surgical procedures, postoperative complications, results and patients’ follow-ups were evaluated.


Introduction
Parapelvic renal cysts are the special type of renal cystic disease. The prevalence of parapelvic renal cysts is 1-3% among all cases of renal cystic disease [1], and their diameter increases with aging, especially in the 50-70 year-old individuals. Other studies reported the occurrence rate is equally common in males and females [2]. Parapelvic renal cysts easily become symptomatic caused by compression of the renal collecting system or the renal pedicle vessels, which may result in pyelocaliceal junction obstruction, ank pain, infection, and complicated stone formation in some cases. Diagnosing a parapelvic renal cyst by Computed tomography (CT) scan and enhancement have an accuracy rate of 80-95% [3]. Meanwhile, CT-scan criteria is used for differentiating benign cysts (Type I-II) from malignant cysts (Type III-IV) according to Bosniak classi cation [4].
Several techniques are used to treatment parapelvic renal cysts disease. Currently available management options for parapelvic cysts include from percutaneous nephroscopic ablation and laparoscopic cyst decortication to exible ureteroscope [5]. In comparison with the other options, the exible ureteroscope approach has the advantage of minimally invasive nature, low complication rate and a short hospital stay [6]. Since 2009, Basiri et al. reported the rst intra-renal cyst incision and drainage [7]. The clinical feasibility of exible ureteroscopic management for parapelvic renal cyst have been con rmed in a larger number of patients, but few studies have investigated the localization of parapelvic cysts during endoscopic surgery. As far as we know, more challenging procedures may be performed if the parapelvic cyst wall is not found during surgery, especially if the cyst wall does not normally bulge into the collection system or the tissue thickness between the collection system and the cyst.
To locate an endoscopic cyst and thereby decrease complicated surgical interventions when our initial attempt to nd the cyst wall by direct observation failed, we tended to perform a study using ultrasoundguided exible ureteroscope in the treatment of parapelvic cyst. We describe the process of localizing parapelvic cysts in dealing and summarize our initial clinical experience.

Patient selection and evaluation
From March 2017 to May 2020, 17 patients with parapelvic renal cysts were admitted to Handan First Hospital. This study retrospectively analyzed clinical data from ultrasound-guided exible ureteroscope in the treatment of parapelvic cyst procedures. The informed consent was obtained throughout the process.
All of the patients received Imaging evaluations included plain lms of the kidneys, ureters and bladder (KUB), renal ultrasonography and CT scanning and computed tomography urography (CTU) to de ne the collecting system anatomy.
The standard of inclusion criteria and exclusion criteria was followed The inclusion criteria were as follows: (1) patients with a Bosniak classi cation of CT imaging were grade I and II;(2) presence of parapelvic cyst larger than 3 cm in size; (3) urinary obstruction and hydronephrosis caused by parapelvic cyst compressing the renal calyx or renal pelvis;(4) ank pain, hemorrhage and some other complications caused by parapelvic cyst;(5) secondary renal calculi larger than 5 mm in size.
The exclusion criteria were as follows:(1) patients with a Bosniak classi cation of CT imaging were grade III and IV;(2) suspicion of severe urinary tract infection;(3) ureteral stricture;(4) history of cardiopulmonary insu ciency Surgical technique A 6Fr Double-J stent (Laekna, Shanghai, China) was placed two weeks before surgery for the dilation of ureter. Urine test and urinary culture were routinely done, antibiotics treatment was administered to the patients with urinary tract infection ndings before surgical treatment. The patient was placed in the lithotomy position and the pre-placed 6Fr Double-J stenting was removed after general anesthesia. Operator cannulated the ureteral ori ce with a hydrophilic guidewire (Cook® Medical, Bloomington, IN, USA) into the renal pelvis. Con rming guidewire placement in the renal pelvis by ultrasound, then the rigid ureteroscope (Richard Wolf, Germany) was used to examine the relevant ureter routinely. A ureteral access sheath (Cook® Medical, Bloomington, IN, USA) was inserted into the ureteropelvic junction to facilitate exible ureteroscopy. The operator surveyed the renal pelvis and calyces sequentially with using exible ureteroscope (Olympus, Tokyo, Japan) to locate parapelvic cysts wall. In addition, handling the renal stones rst if the cyst combined with calculus, the renal stones were fragmented to less than 3 mm with holmium laser (Raykeen, Shanghai, China). The large fragments were removed by a stone basket (Bard, Georgia, USA) to prevent the fragments entering the cystic cavity after the wall was opened.
Generally, the parapelvic cyst appeared transparent with blue areas in ureteroscope vision when we tried to search the cyst wall by direct visualization initially. To avoiding renal pedicle injury, the renal calyces were chosen as the best incision point, and then renal pelvis was the second choice. The holmium laser was used to cut the cyst wall about 2 cm to enable communication with the collecting system.
If the typical blue wall was not found, searching a suspicious wall which protruded into the renal pelvis, the exible ureteroscope was guided close to the suspicious wall in real time by using ultrasound (SIUI, Guangzhou, China). Before the holmium laser was triggered for drainage, the operator Con rmed that the exible ureteroscope was pushing against the cyst wall under the ultrasound imaging (Video 1). The incision was performed on an appropriate drainage site and the typical smoking sign was observed in ultrasound ( Figure 1). For drainage, the proximal double-J stent was coiled in the cyst cavity which was removed 1-3 months later.
All patients were followed-up 3, 6 and 12 months later in our outpatient department. Ultrasonography or CT examinations were used to detect the recurrence of parapelvic cyst and residual stones, patients with cyst shrinks to half of its original size by imaging examination on 6 months were considered as effective therapy. In addition, clinically insigni cant residual stone was de ned as less than 4 mm in largest diameter.
Statistical analysis SPSS 26.0 software was used to analyse the extracted data. T-test was used for comparing quantitative value and χ2 test was used for qualitative values. p < 0.05 was de ned as a statistically signi cant difference.

Results
A total of 17 patients with parapelvic renal cysts, composed of 8 males and 9 females, received endoscopic management by exible ureteroscopy. All operations were conducted successfully and no patients were received open management in surgery. The mean patient age was 52.8 ± 15.1 years (range 45-79 years). There were 6 cases of simple parapelvic cysts and 11 cases of parapelvic cysts with ipsilateral renal calculi. The mean size of cyst and stone were 53.6 ± 7.8 mm (range 40-65 mm) and 10.1 ± 1.7 mm (range 8-12 mm) on preoperative CT scan, respectively (Table 1).
During marsupialization, 10 patients underwent endoscopic management by simple exible ureteroscopy, 7 patients transformed to ultrasound-guided exible ureteroscopy because of locating the cyst wall di cultly. The mean operative times of simple exible ureteroscopy and ultrasound-guided exible ureteroscopy were 25.9 ± 8.7 minutes and 37.1 ± 10.1 minutes, respectively. No severe postoperative complications (such as massive hemorrhage or renal perforation). Postoperative fever( 38.5℃) occurred in 2 cases, backache in 4 cases, the clinical symptomswere alleviated 3-5 days after surgery. The followup for 12 months showed 12 cysts became undetectable, while 5 cysts decreased in size by at least half (Table 2).

Discussion
Renal cyst is a common cyst disease and it occur 5% of the cysts in the general population, most of them do not require any treatment [8]. Parapelvic renal cysts are rare entities of renal cysts which adjacent to the collecting system and the vessels of renal hilum. The ratio of men to women is similar, most patients are older than 50 and the age is directly related to the increase of cyst diameter [9]. However, parapelvic cysts may cause clinical symptoms earlier than simple renal cysts and are more frequently associated with pain, hematuria, infection, hypertension, hydronephrosis and stone formation [10,11,12]. Thus earlier surgical intervention is required than simple renal cysts.
To date, some studies have reported exible ureteroscopic treatment of this disease and have been proven to be feasible and safe in patients which was selected. Comparing with percutaneous resection or ablation, the work access sites associated with percutaneous nephrostomy (PCN) inevitably cause renal injury, such as severe perinephritis, retroperitoneal abscess and secondary ureteropelvic junction obstruction. The complications often emerge with ranging from 29% to 83% [13,14]. Comparing with the laparoscopic unroo ng, the latter has a high risk of injury to the renal cortex and renal pedicle since the parapelvic cysts are usually surrounded by renal parenchyma [7,15]. The retrograde approach may be less invasive for entirely endophytic cysts. exible ureteroscopic technique has lowered the risk of serious complications [16].
The location of the renal cyst wall is a crucial step of marsupialization for treatment of parapelvic cysts. Liaconis et al reported that in ureteroscope vision, the light blue color of cystic wall was helpful for location of cyst [17]. We also found that some case of typical cystic in our study, however, these features were not discovered if the cyst wall was relatively thick. Another study by Zhixian Wang et al reported methylene blue injection via percutaneous renal cyst puncture to identify the parapelvic cyst, this method successfully located the cystic wall in their research [18]. But in previous studies [15], we found that the blue cyst wall which was injected with methylene blue was also identi ed di culty If the typical capsular wall was not found during surgery. The cystic wall has the same color as other parts of the renal pelvis because of relatively thick, it is a challenging for the operator to locate the cystic wall and to choose the area for incision.
The primary aim of this study was to present a method for locating cystic wall during routine exible ureteroscopy failed to search for parapelvic cysts. Intraoperative ultrasound has been used increasingly in recent years. Ultrasound has the advantages of real-time monitoring of cysts and guided exible ureteroscope, which can help us to nd cystic wall and adjust the incision direction. Kang N et al have reported the experience of exible ureteroscope combined ultrasound to help search for parapelvic cysts, the holmium laser can be presented linear high-echo and cysts can be presented low-echo under ultrasound image [19]. Meanwhile, the adjacent relationship between exible ureteroscope and cyst can be showed under ultrasound image, to choose the best area for incision and inner drainage. In our study, more than half cysts could be found under ureteroscopic vision, as we demonstrated successfully in 10 patients in this study. In cases where the cyst wall had the same color as other parts of the renal pelvis, the ultrasound had been employed. We found this technique can eliminate the methylene blue injection via percutaneous renal cyst puncture and reduce the patient's pain without prolonging the operation time.
During a mean follow-up period of 14 months (range 12-18 months) with ultrasound and CT showed no cyst recurrence. The results suggest that our techniques prevent further compression on the collecting system and promote complete drainage of cystic uid. We provide an alternative method which can be selected for patients with parapelvic cysts.
Our research has limitations of small patient sample, since the parapelvic cysts are not relatively common. Meanwhile the inherent defects of retrospective study and lack of long-term follow-up led to aws in the study. The number of patients who required ultrasound-guided exible ureteroscopy was not many. In this situation, designing and conducting a randomized controlled trial was di cult, we chose to perform a retrospective research instead, which could explain there was no control group.

Conclusion
Ultrasound guidance as a modi ed method for the treatment of parapelvic cysts by exible ureteroscopy. According to our research results, this procedure is a feasible, safe, and effective approach to parapelvic cysts. Further studies with large samples and longer follow-ups need to be assessed for long-term e cacy. 14.5 ± 3.2 8.9 ± 2.6 .005 The expression of continuous variables and categorical variables were mean ± standard deviation and n (%), respectively. .540