Introduction
Surgery is the cornerstone of treatment for rectal cancer [
1]. Several randomized controlled trials have ascertained comparable oncological outcomes of laparoscopic rectal cancer surgery in comparison to open surgery, along with the short-term advantages in terms of postoperative pain, bowel function, and postoperative hospitalization [
2‐
5]. Despite the increased application of laparoscopic procedures, laparoscopic total mesorectal excision (LaTME) for mid/low rectal cancers can be technically demanding, particularly in obese male patients with a narrow pelvis. Currently, neoadjuvant chemoradiotherapy (NCRT) followed by total mesorectal excision (TME) is accepted as the standard treatment for patients with locally advanced rectal cancer (LARC) [
6,
7]. However, tissue inflammation, edema, or fibrosis following NCRT can impede vision and hamper dissection maneuvers, thereby adding to the surgical difficulty of laparoscopic surgery for rectal cancer after NCRT. Considering the technical and ergonomic advantages, robotic TME might help to overcome the limitations of LaTME in the confines of the pelvis [
8]. Additionally, a new down-to-up approach to rectal cancer surgery, transanal TME (TaTME), appears to be an alternative surgical option for rectal cancers, especially in individuals with a narrow pelvis [
9]. Therefore, the preoperative evaluation of surgical difficulty could help to plan the optimal surgical approach.
Besides surgical skills, there are several well-established factors associated with the increased surgical difficulty of LaTME, including male sex, high body mass index (BMI), prior abdominal surgery, a low-lying tumor, and advanced tumor stage [
10,
11]. The pelvic anatomy can also influence the operative difficulties of LaTME, including—but not limited to—a prominent sacral promontory, an acutely curved sacrum, or a narrow pelvic outlet. Recently, magnetic resonance imaging (MRI)-based pelvimetry, including the pelvic dimensions and angles, has been proposed as a useful tool for evaluating the surgical difficulties of LaTME [
12‐
14]. As expected, LaTME in a narrow pelvis can be more difficult to perform due to radiation-induced tissue inflammation, edema, or fibrosis. Besides, male patients with rectal cancer usually represent more challenging cases to surgeons, given that the female pelvis is generally more accessible than the male pelvis during pelvic surgery. Thus, performing LaTME in male patients after NCRT is expected to be more technically challenging.
However, the surgical difficulties of LaTME in male rectal cancer patients following NCRT have not been robustly explored [
13,
15]. To address the gap in the literature, we aimed to investigate the clinical and pelvimetric factors that predict surgical difficulties of LaTME after NCRT and to develop a predictive nomogram to assist in the selection of the optimal surgical approach for mid/low rectal cancer after NCRT.
Discussion
Currently, studies focused on the surgical difficulty of LaTME after NCRT for male rectal cancer patients are limited [
13,
15]. The present study demonstrated that higher BMI, shorter tumor distance from the anal verge, larger tumor diameter, shorter interspinous distance, and smaller angle
α could help predict the surgical difficulty of LaTME after NCRT. We then constructed a nomogram predicting the surgical difficulty of LaTME after NCRT, which may be helpful when selecting the surgical approach preoperatively.
BMI, an easily obtainable parameter of obesity, is also useful in predicting surgical difficulty[
10]. We found that higher BMI values were associated with higher degree of surgical difficulty when performing LaTME in male patients following NCRT, which was consistent with previous findings. A larger tumor diameter usually indicates a larger tumor volume, which may restrict the pelvic working space, and thus increases the surgical difficulty of LaTME [
19]. The pelvic space becomes narrower as rectal cancers approach closer to the anal verge when performing rectal dissection, transection, and anastomosis; thus, the surgical difficulty may increase as well [
10]. Consistent with previous studies, the present study demonstrated that a larger tumor diameter and shorter tumor distance from the anal verge were independent predictors of the surgical difficulty of LaTME after NCRT.
Tumor downsizing may reduce the surgical difficulty of rectal cancer surgery. In our daily clinical practice, we have found that tumor downsizing in good responders to NCRT may facilitate surgical dissection. In the present study, we found that the tumor diameter independently predicted high surgical difficulty in laparoscopic TME in rectal cancer surgery (univariate
P < 0.001, multivariate
P = 0.004). While NCRT could induce tumor downsizing and downstaging, dissection of the mesorectum is often hindered by edema, mist, and exudates induced by NCRT, and thus adds to the surgical difficulty. Several surrogate markers have been utilized to estimate the surgical difficulty of TME, including the operative time, blood loss, conversion, circumferential resection margin (CRM) status, and postoperative complications [
11,
20]. Considering that impaired surgical quality and an eventful postoperative course might compromise the oncological outcome and survival [
21], we herein applied both intraoperative and postoperative parameters to better define surgical difficulty by modifying the definition previously proposed by Escal et al. [
12].
Indeed, surgical expertise is one of the most important factors influencing the surgical difficulty of LaTME. In our study, surgeries were performed by a group of highly experienced surgeons. Among these cases, LaTME after NCRT was performed with a very low conversion rate (2%) and a low incidence of postoperative morbidity (15.6%); in 12.2% of the cases, LaTME after NCRT was considered to be associated with a high degree of surgical difficulty, which was similar to the rate reported by Escal et al. (12.8%) [
12].
In general, male patients have a narrower and deeper pelvis than female patients, which may result in more challenging LaTME [
22]. Pelvic anatomical factors, such as a narrow pelvis, a prominent sacral promontory, an acutely curved sacrum, and a shallow sacral angle represent anatomical bottlenecks of the pelvis and add to the surgical difficulty of LaTME for rectal cancer [
15,
23]. In addition, these limitations cannot be completely overcome by surgical expertise. To date, there is increasing interest in MR-based pelvimetry to predict the surgical difficulty of LaTME [
10,
11,
20]. However, the optimal pelvimetric parameters influencing surgical difficulty remain inconsistent in the literature. In this study, we used 14 pelvimetric parameters based on MRI, including 7 dimensions, 4 angles, and 3 areas of the pelvis. The univariate analyses demonstrated that shorter interspinous distance, smaller angle
α, larger angle
δ, larger mesorectal area, and larger mesorectal fat area were associated with high surgical difficulty in LaTME after NCRT. The multivariate analysis demonstrated that a shorter interspinous distance and smaller angle
α were independently associated with a high degree of surgical difficulty, which was in good accordance with previous findings [
12,
14]. A smaller angle
α may limit the maneuverable space, and make for unsatisfying counter traction turns, thereby increasing the surgical difficulty of LaTME. Not surprisingly, our study also found that a shorter tumor distance from the anal verge was independently associated with high surgical difficulty of LaTME following NCRT. In addition, a larger tumor within the bony pelvis could increase the operative difficulty [
24]. Similarly, our results reaffirmed that a larger tumor diameter was an independent predictor of high surgical difficulty in LaTME following NCRT.
Great efforts have been devoted to building scoring systems that predict the surgical difficulty of LaTME for rectal cancer [
12,
14]. By incorporating both clinical and pelvimetric parameters, the present study developed a nomogram predicting cases in which LaTME after NCRT would be associated with high surgical difficulty; this nomogram showed good discriminative power. Using this nomogram, early surgical trainees can select appropriate cases to minimize adverse outcomes and reduce the impact of inexperience. Besides, patients could be informed of surgical difficulty as well as perioperative risks and complications. Currently, robotic rectal cancer surgery is gaining acceptance due to several advantages over laparoscopic surgery [
25]. TaTME is a promising technique that could overcome the limitations of LaTME, especially in obese patients [
26]. Our nomogram might assist in the preoperative selection of an appropriate surgical approach for LARC patients after NCRT (e.g., open, laparoscopic, robotic, or transanal).
Robotic TME might help to overcome the limitations of LaTME in the confines of the pelvis. As reported previously [
8], high BMI, use of NCRT, and lower tumor levels were significantly associated with a longer operation time, which was in line with our findings. Different from our results, pelvimetric parameters were not associated with a longer operation time in patients undergoing robotic TME. One potential explanation could be the ergonomic advantages and improved dexterity of robotic TME. TaTME, which is TME with a down-to-up approach, is a promising alternative for rectal cancers with a narrow pelvis. Ferko et al. [
27] found a correlation between TME quality and pelvimetric parameters, and suggested that it could be used as a tool for selecting candidates for TaTME.
The present study was associated with several limitations. First, this study was a monocentric study based on a retrospective analysis. Second, the sample size was relatively small. Third, higher surgical difficulty may potentially affect the quality of TME or pathological CRM and thus impairs the oncological outcome and survival [
21]. Since the present study aimed to identify predictors of surgical difficulty of LaTME in male patients after NCRT, we did not evaluate oncological factors, which could be a limitation of our study. Fourth, our predictive nomogram required further validation in other independent patient cohorts. Despite these limitations, the present study might add to the understanding of the predictive value of MRI-based pelvimetry when estimating the surgical difficulty of LaTME in male LARC patients after NCRT.
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