Accurately predicting and managing the surgical duration is important in reducing perioperative complications and hospital costs [12–14]. Although some factors associated with prolonged operative time during RALP have been reported, no study has evaluated the relationship between prostate shape and surgical duration. To the best of our knowledge, this is the first report to demonstrate that the shape of the prostate affects the difficulty of RALP.
"Roundness" was used as an index to evaluate the roundness of the prostate in this study. Roundness is the measure of how close the shape of an object approaches a mathematical circle, which is calculated by a ratio of the radii of the inscribed circle and circumcircle that share the same center. We evaluated prostate sphericity by measuring the roundness of the prostate at the largest axial slice by MRI (Fig. 1). The console time was adopted as an objective indicator for assessing surgical difficulty. A scatter plot was created to assess the relationship between console time and roundness. In the whole cohort analysis, the console time increased with increased roundness. Furthermore, in subgroup analysis of patients with a large prostate volume (≥ 40 cc), prostate roundness was strongly correlated with the console time. Our results indicated that RALP for large and spherical prostates requires advanced surgical techniques. RALP is now widely employed and young urologists are expected to perform more RALP procedures in the future. This study may help in selecting cases for a novice surgeon.
The following are possible reasons why surgery for a spherical prostate is difficult: (1) When the bladder neck is divided, it is difficult to imagine the anatomical boundary three-dimensionally because the cross-section is not flat (Fig. 4a). (2) When dividing the lateral pedicle, protrusion of a spherical prostate to the posterior side shortens the distance of the pedicle (Fig. 4b). (3) Lastly, when treating the apex side of the prostate, the space between the apex and endopelvic fascia and/or pubic bone is narrowed (Fig. 4c).
A strength of our study is that assessing the difficulty of surgery based on roundness is clinically practical because it is simple and does not require additional costs. Most patients undergoing radical prostatectomy inevitably undergo preoperative MRI. It is simple to draw the inscribed and circumscribed circles of the prostate on MRI, and measure the radius of each. However, this study has some limitations. Our results were based on two surgeons at a single institution, which may have limited the validity of our findings. Each performed more than 50 RALP procedures by the starting point of this study, but favorable operative outcomes were reported to be achievable after a longer learning period . No patients in our study cohort received "extended" lymphadenectomy, which is recommended in cases with an estimated risk of node positive > 5% . Therefore, the difference in the skills of the surgeons and operative procedures may affect the operation time and the impact of prostate shape. In addition, the shape of the prostate was evaluated using single MR images. Evaluation of prostatic sphericity may be more accurate by adding MR images of coronary and sagittal sections.
In conclusion, roundness was significantly correlated with console time. The spherical shape of the prostate affects the difficulty of RALP, especially in patients with a large prostate volume. Thus, measuring the roundness of the prostate before surgery can lead to better estimates of the operative time, which may help determine the risk status of patients or identify cases appropriate for novice urologists.