Comparison of anatomical changes in computed tomography (CT) scan in supine position and prone position with respect to percutaneous nephrolithotomy (PCNL)

Annals of Urology (ISSN 2767-2271) Comparison of anatomical changes in computed tomography (CT) scan in supine position and prone position with respect to percutaneous nephrolithotomy (PCNL). Dr. Kutumba Chandra Yella 1 , Dr. Ketan Vartak 2 , Dr. Dhaval A Rasal 3 , Dr. Shams Abdulkadir Iqbal 4 , Dr. Devendra Kumar Jain 5 , Dr. Isha Sandip shah 6 , Dr. Shashank Patil 7 , Dr. Sanjay P Dhangar 8 , Dr. Hrishikesh Satish Deshmukh 9 , Dr. Pawan Rahangdale 10 Corresponding author Dr Shams Abdulkadir Iqbal, Associate professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Email : [email protected] Received Date : July 03, 2024 Accepted Date : July 04, 2024 Published Date : August 05, 2024 ABSTRACT Objective: To compare the anatomical organ positional changes, renal access tract length and maximum renal access angle in relation to the kidney in supine and prone positions through CT scan images. Methods: CT Urography was performed in 52 patients with various urological complaints in supine and delayed images in prone position. A comparison in both supine and prone position was done to analyse the organ interposition, pleural interposition, mean access tract length, maximum renal access angle for PCNL. Results: The difference in the organ interposition was not statistically significant whereas Pleural interposition was more common in the prone position compared to supine position on both the right (9 vs 2, p = 0.03) and left (3 vs 0, p = 0.24). Mean access tract length was shorter in prone position on both the right (69.93mm vs 61.74mm, p <0.001) and left (69.78mm vs 63.57mm, p <0.001) sides. Maximum renal access angle was greater in the supine position on both the right (73.570 vs 69.030, p = 0.4) and left (73.780 vs 64.700, p = 0.025) sides with statistical significance on the left side. Conclusion: PCNL in prone position has an advantage of having shorter access tract length compared to supine position. PCNL in supine position has an advantage of having a wider access angle compared to prone position. Upper calyx puncture for PCNL in prone position has a high chance of pleural interposition. Keywords: organ interposition, pleural interposition, maximum renal access angle, renal access tract length, ct scan prone vs supine, pcnl. INTRODUCTION Percutaneous nephrolithotomy (PCNL) is a commonly performed endourological procedure and a gold standard for renal stones >2cm. Organ interposition, renal access tract length and renal access angle are important parameters for planning the procedure of percutaneous nephrolithotomy (PCNL). We have come a long way since 1941 when Rupel and Brown performed the first nephroscopy. A rigid cystoscope was passed into the kidney following open surgery [1]. In 1978, it was Arthur Smith, along with Kurt Amplatz who took PCNL to the heights that it stands today [2,3,4]. The prone position was presumed to be the standard of PCNL and the safest approach in preventing colonic perforation. Valdivia-Uria was the first person who showed that supine PCNL could be done with equal complication rates and success rates and has the advantage in terms of patient positioning and management during anaesthesia [5,6]. A lot of new enthusiasm is being generated among the urologists all over the world to convert to supine PCNL from the prone PCNL. There are two groups claiming the superiority of supine over prone PCNL or prone over supine PCNL [9]. Traditionally computed tomography (CT) scan is done in supine position and the PCNL is being done in prone position. Although there are substantial number of publications available to take care of this discussion [10,11,12], there is a very scanty literature available on the actual anatomical variations of surrounding structures like colon, liver, and the spleen in relation to the kidney in both prone and supine positions. Our present study aims to compare the anatomical organ positional changes in relation to the kidney in supine Original Research Article 1www.directivepublications.org

Annals of Urology (ISSN 2767-2271) and prone positions through CT scan images and to study the differences in the renal access tract length and maximum renal access angle in supine and prone positions through CT scan images and its likely implications [1,4,8,10,11,12] on performing PCNL. MATERIALS & METHODS The patients enrolled in this study were informed about the study and a verbal and a signed informed consent was taken to participate in this study. Approval of the ethical committee of institute xxxx was taken (REF: BVDUMC/IEC/15). 52 patients who underwent CT urography as a part of their evaluation for various urological complaints were included in this study. These patients were imaged in both supine and prone positions. The non-contrast and nephrogenic images were obtained in supine position and the delayed excretory images were obtained in prone position. None of the patients were exposed to increased radiation. Inclusion criteria Patients above 18 years of age with creatinine values within the reference range (adult male: 0.73 -1.18 mg/dl, adult female: 0.55 – 1.02 mg/dl) were included in this study for CT scan to be done in plain and contrast phases. Exclusion criteria Patients below 18 years of age, patients with anatomical and renal anomalies, patients with high creatinine values (beyond the reference range), and patients with a history of renal surgeries were excluded from this study. Organ interposition, renal access tract length and maximum renal access angle were calculated using supine and prone CT scan images. Organ interposition was seen as presence of any organ (liver, spleen, or colon) along the line from the posterior most calyx to the posterior axillary line in the upper, middle, and lower poles of both the right and the left kidney. If there was presence of organ interposition along the above-mentioned path, it was noted as “yes” and if there was no organ interposition, it was noted as “no” (figure 1-4). Figure 1. Shows presence of organ (liver) interposition in supine position. Original Research Article 2www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Figure 2. Shows no organ interposition in supine position. Figure 3. Shows presence of organ (liver) interposition in prone position. Original Research Article 3www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Figure 4. Shows no organ interposition in prone position. We have done multiple pilot studies to mark the posterior axillary line to visualize that mark on the CT scan image. We first used a metallic wire, but it led to artefacts. We then used a 9 fr infant feeding tube and it was not clearly visible. We then used a 6 fr ureteric catheter to mark the posterior axillary line by affixing with a tape over the posterior axillary line in standing position. It showed no artefacts and it was clearly visible on CT scan images. The renal access tract length was calculated from the posterior axillary line on the surface of the skin to the posterior most calyx in the middle and lower poles, and the posterior most aspect of the lateral calyx in the upper pole (figure 5,6). This technique was used to measure the access tract lengths of upper, middle, and lower pole. Maximum renal access angle was measured or defined as angle between the lateral margin of paraspinous muscle to the posterior most border of either the liver, spleen, or colon (figure 7,8). We have also seen for the proportion of pleural interposition along the path from the posterior axillary line to upper calyx in both supine and prone positions on the right and left sides. If there was presence of pleural interposition along the above- mentioned path, it was noted as “yes” and if there was no pleural interposition, it was noted as “no” (figure 9,10). Proportion of organ interposition, mean access tract lengths and maximum renal access angle were calculated and tabulated using the same calyx in supine and prone images for upper, middle, and lower poles for right and left kidneys and statistical significance was calculated. Statistical analysis was performed using Microsoft excel. To compare the measurements, student’s t-test was used. Original Research Article 4www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Figure 5. Shows access tract length in Supine Position. Figure 6. Shows access tract length in prone position. Original Research Article 5www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Figure 7. Shows maximum renal access angle in supine position. Figure 8. Shows maximum renal access angle in prone position. Original Research Article 6www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Figure 9. Shows presence of pleural interposition in prone position. Figure 10. Shows no pleural interposition in supine position. Original Research Article 7www.directivepublications.org

Annals of Urology (ISSN 2767-2271) RESULTS 52 patients were included in this study. There were 23 males and 29 females ranging in age from 22 years to 70 years (mean: 44.17). Organ interposition The results are summarized in table 1. The proportion of organ interposition for the upper, middle, and lower pole of the kidneys were compared in supine and prone positions on both the right and the left side. The difference in the organ interposition between the supine and the prone positions was not statistically significant. Table 1 ORGAN INTERPOSITION (n = 52) RIGHT KIDNEY YES NO p-value UPPER POLE Supine 33 19 0.42 Prone 29 23 MID POLESupine 6 46 0.51 Prone 4 48 LOWER POLE Supine 1 51 0.99 Prone 2 50 LEFT KIDNEY YES NO p-value UPPER POLE Supine 32 20 0.12 Prone 24 28 MIDDLE POLE Supine 3 49 0.49 Prone 6 46 LOWER POLE Supine 2 50 0.27 Prone 6 46

Pleural interposition The results of pleural interposition are summarized in table 2. On the right side, 2 patients had pleural interposition in supine position, while 9 patients had pleural interposition in prone position (p = 0.03). On the left side, no patient had pleural interposition in supine position, while 3 patients had pleural interposition on prone position (p = 0.24). These differences were statistically significant on right side but not on the left side. Table 2 PLEURAL INTERPOSITION (n=52) YES NO p-value RIGHT SIDE Supine 2 50 0.03 Prone 9 43 LEFT SIDE Supine 0 52 0.24 Prone 3 49 Renal access tract length The results are summarized in table 3. The mean right sided supine tract length was 69.93 mm vs 61.74 mm in the prone position (p = <0.001). The mean left sided supine tract length was 69.78 mm vs 63.51 mm in prone position (p = <0.001). The access tract length was less in the prone position compared to supine position on both the right and left sides. The differences between supine and the prone positions were statistically significant. Table 3 ACCESS TRACT LENGTH VALUES (n=52) RIGHT KIDNEY Mean p-value UPPER POLE Supine 66.17 0.015 Prone 61.77 MID POLE Supine 67.78 0.008 Prone 60.95 LOWER POLE Supine 76.27 <0.001 Prone 64.68 LEFT KIDNEY Mean p-value UPPER POLE Supine 66.18 0.03 Prone 61.77 MIDDLE POLE Supine 67.28 0.02 Prone 61.23 LOWER POLE Supine 75.88 0.008 Prone 67.71 ACCESS TRACT LENGTH OVERALL VALUES Mean p-value RIGHT KIDNEY Supine 69.93 <0.001 Prone 61.74 LEFT KIDNEY Supine 69.78 <0.001 Prone 63.57 Original Research Article 8www.directivepublications.org

Annals of Urology (ISSN 2767-2271) Maximum renal access angle The results are summarized in table 4. The mean right sided supine access angle was 73.570 vs 69.030 in the prone position (p = 0.4). The mean left sided supine access angle was 73.780 vs 64.700 in the prone position (p-value = 0.025). The maximum renal access angle was greater in the supine position compared to the prone positions and the differences between the supine and the prone positions were statistically significant on the left side but not on the right side. Despite the differences between supine and prone positions were not statistically significant for the right side, the differences were statistically significant for the right lower pole. Table 4 ACCESS ANGLE VALUES (n=52) RIGHT KIDNEY Mean p-value UPPER POLE Supine 30.43 0.81 Prone 32.13 MID POLE Supine 82.30 0.87 Prone 81.07 LOWER POLE Supine 107.98 0.02 Prone 93.88 LEFT KIDNEY Mean p-value UPPER POLE Supine 30.43 0.61 Prone 32.12 MIDDLE POLE Supine 90.32 0.04 Prone 76.29 LOWER POLE Supine 96.85 0.01 Prone 80.15 ACCESS ANGLE OVERALL VALUES Mean p-value RIGHT KIDNEY Supine 73.57 0.4 Prone 69.03 LEFT KIDNEY Supine 73.78 0.025 Prone 64.70 DISCUSSION Percutaneous entry into the kidney was initially started with the prone position and now it is also being done in supine position. The reason for preferring the prone position over supine position was regarding the presumed decreased risk of visceral injury in prone position. The measurements were calculated using axial images as like all the prior studies done to evaluate anatomical changes between patient’s position were done using axial images [7,8,9]. The access tract length is important for many reasons. The access sheath within the lumbar fascia and parietal muscles acts as a fulcrum [9]. As a result, the farther this is from the skin towards the collecting system, the lesser is the manoeuvrability of the sheath within the collecting system leading to lesser stone free rates. This leads to more torque being applied and high chances of bleeding. As the access tract length increases, longer access sheaths are required. In our current study, the mean access tract length was significantly shorter in prone position compared to supine on both the right and left sides. The right side was shorter by 8.19 mm (p <0.001) and the left side was shorter by 6.21 mm (p <0.001). Our findings were similar and supported by the study published by Duty et al [9]. The access angle represents the area for all the potential points of entry for access tracts. Therefore, a wider access angle gives a larger safety margin for entry into the collecting system, thereby facilitating higher stone free rates. In our study, it was found that the mean access angle in the supine position on the right side is 73.570 vs 69.030 in the prone position (p = 0.4). The mean left sided access angle in the supine position was 73.780 vs 64.700 in the prone position (p = 0.025). The differences between the supine and the prone positions were statistical significance on the left side but not on the right side. Our findings were contrary to the study published by Duty et al [9], which described a wider access angle in the prone position. Our study has a few limitations 1. The study was conducted only through CT scan images without any clinical correlations. We thought that correlating with clinical findings during PCNL procedure will have surgeon’s bias as well as case bias. 2. We have used a fixed mark of entry into the collecting system (which is the posterior axillary line) to compare the organ interposition in prone position as compared to supine. As a result, our studies showed a higher organ interposition. Whereas in clinical scenario, the surgeon will change the entry point into the calyx as per the convenient entry into the desired calyx. 3. Due to increased risk of radiation, we have taken plain and nephrogenic phases of CT scan in supine position, and excretory phase in prone position. Had the plain nephrogenic and excretory phase been done in both the prone position and supine position individually, the amount of radiation would have increased. But this did not change the outcome of our study.” Original Research Article 9www.directivepublications.org

Annals of Urology (ISSN 2767-2271) CONCLUSION Puncture for PCNL attempted in prone position could have an advantage of having a shorter access tract length compared to supine position, thereby giving more manoeuvrability for the access sheath within the collecting system. Puncture for PCNL attempted in supine position (especially for middle and lower calyx) could have an advantage of having a wider access angle compared to prone position, thereby giving wider access to puncture a targeted calyx. Upper calyceal puncture for PCNL attempted in prone position has a high chance of pleural interposition compared to supine position, with the right sided upper calyceal puncture having a higher chance of pleural interposition (statistically significant). Organ interposition, though not statistically significant, puncture of upper calyx has a higher chance of organ interposition in supine position compared to prone position. Therefore, if an upper calyceal puncture is attempted in prone position, it could have a less likelihood of having an organ interposition, but could have a high likelihood of pleural interposition compared to supine position. But this study is based on the interpretation of findings of the CT scan images and need clinical correlation. Author names and affiliations Author 1: Dr. Kutumba Chandra Yella, Senior Resident, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 2: Dr. Ketan Vartak, Professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 3: Dr. Dhaval A Rasal, Assistant professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 4: Dr. Shams Abdulkadir Iqbal, Associate professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 5: Dr. Devendra Kumar Jain, Professor and Head, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 6: Dr. Isha Sandip shah, Junior resident, department of Radiology, Bharati Vidyapeeth (Deemed to be University). Author 7: Dr. Shashank Patil, assistant professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 8: Dr. Sanjay P Dhangar, assistant professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 9: Dr. Hrishikesh Satish Deshmukh, Associate professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). Author 10: Dr. Pawan Rahangdale, Assistant professor, Department of Urology, Bharati Vidyapeeth (Deemed to be University). DECLARATIONS Ethics Committee Approval Ethical approval for this study was obtained from INSTITUTIONAL REVIEW BOARD (BVDUMC/IEC/15) Consent for publication Written informed consent was obtained from all subjects before the study. Availability of data and material The datasets used and/or analysed during the current study are available from the corresponding author on request. Competing interests The author(s) declare(s) that they have no competing interests. Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors Acknowledgements: None Conflicting interests The Authors declare that there is no conflict of interest. REFERENCES 1. Rupel E, Brown R. Nephroscopy with removal of stone following nephrostomy for obstructive calculus anuria. J Urol 1941;46:177-82. 2. Smith AD, Lange PH, Miller RP, Reinke DB. Introduction of the Gibbons ureteral stent facilitated by antecedent percutaneous nephrostomy. J Urol 1978;120:543-544. 3. Smith AD. A personal perspective on the origins of endourology and the endourological society. J Endourol 2002;16:705-8. 4. Castaneda-Zuniga WR, Clayman R, Smith A, Rusnak B, Herrera M, Amplatz K. Nephrostolithotomy: Percutaneous techniques for urinary calculus removal. J Urol 2002;167:849-853. 5. Valdivia-Uria JG, Lanchares E, Villarroya S, Taberner J, Abril G, Aranda JM. Nefrolitectomia percutanea: Tecnica simplificada (nota previa). [Percutaneous nephrolithotomy: simplified technique (preliminary report)] Arch Esp Urol 1987;40:177-180. 6. Valdivia Uria JG, Valle Gerhold J, López López JA, et al. Technique and complications of percutaneous nephroscopy: experience with 557 patients in the supine position. J Urol. 1998;160:1975-1978. 7. Ray AA, Chung DG, Honey RJ. Percutaneous nephrolithotomy in the prone and prone-flexed Original Research Article 10www.directivepublications.org

Annals of Urology (ISSN 2767-2271) positions: anatomic considerations. J Endourol. 2009;23:1607-1614. 8. Tuttle DN, Yeh BM, Meng MV, et al. Risk of injury to adjacent organs with lower-pole fluoroscopically guided percutaneous nephrostomy: evaluation with prone, supine, and multiplanar reformatted CT. J Vasc Interv Radiol. 2005;16:1489-1492. 9. Brian Duty, Arthur Smith, et al. Anatomical Variation Between the Prone, Supine, and Supine Oblique Positions on Computed Tomography: Implications for Percutaneous Nephrolithotomy Access. Urology. 2012 Jan;79(1):67-71. 10. Mulay A, Mane D, Mhaske S, Shah AS, Krishnappa D, Sabale V. Supine versus prone percutaneous nephrolithotomy for renal calculi: Our experience. Curr Urol 2022;16 (1):25-29. 11. Hopper KD, Sherman JL, Luethke JM, Ghaed N. The retrorenal colon in the supine and prone patient. Radiology. 1987 Feb;162(2):443-6 12. Kannan D, Quadri M, Sekaran P G, et al. (July 16, 2023) Supine Versus Prone Percutaneous Nephrolithotomy (PCNL): A Single Surgeon’s Experience. Cureus 15(7): e41944. Original Research Article 11www.directivepublications.org

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