The impact of pelvimetry data on rectal cancer surgery—a systematic review

Introduction

The management of rectal cancer is changing rapidly secondary to the adoption of total neoadjuvant therapy (TNT) in locally advanced cases and possibly a wait-and-watch approach in cases with complete clinical response. A large proportion of patients will have incomplete response and will require operative intervention, i.e., total mesorectal excision (TME) for the treatment of middle to low-rectal cancers. Various prognostic factors such as T- and N-stage, lymphovascular and perineural invasions, extramural invasion, circumferential resection margin and distal resection margins have been implicated for the long-term survival outcomes of rectal cancer patients (1,2). Amongst them, the quality of TME has significant impact on disease-free and overall survival (3).

Despite the better understanding of pelvic anatomy, achieving complete TME can be technically demanding. Professor Heald in the 1980s demonstrated the Basingstoke experience that complete TME itself drastically reduced the local recurrence rates (4). The recent randomized controlled trials demonstrated at least non-inferiority of laparoscopic TME when compared to open surgery, in experienced laparoscopic surgeons (5-7). It continues to be a challenge to colorectal surgeons when confronted with a “difficult pelvis”. The “difficult pelvis” is normally described and observed in males, obese patients, large and locally advanced rectal cancers, and those post-neoadjuvant radiotherapy. Due to these factors, the quality of TME can be compromised.

Unfortunately, there is no widely accepted definition for the “difficult pelvis”. Several studies have described the use of pelvic dimensions such as mesorectal fat area (MFA), interspinous distance (IS), pelvic inlet (PI) and intertuberous distance (IT) to objectively define surgical difficulty when operating within the constraints of the pelvis. The aim of this systematic review is to evaluate the usefulness of pelvimetric data in assessing surgical difficulty for rectal cancer and correlation with outcomes. We present this article in accordance with the PRISMA reporting checklist (available at https://ales.amegroups.com/article/view/10.21037/ales-24-12/rc).

Methods

Search strategy

A literature search was performed using major PubMed, Embase, and Cochrane Library databases independently by two reviewers (M.F.B.A.R. and Z.Q.N.). A third reviewer (M.T.) was available to resolve any discrepancy. The search was performed with a combination of the terms “rectal cancer”, “rectal neoplasm” and “pelvimetry”. The final search was completed in January 2024. Further studies were identified by cross-checking the references of the above studies. This systematic review was registered with PROSPERO ID: CRD42023446110.

Eligibility criteria

Studies reporting the use of image-based pelvimetry—computed tomography (CT) or magnetic resonance imaging (MRI) to determine surgical difficulty were included. Surgical difficulty was the primary outcome measured. The surgical difficulty was assessed using a combination of surrogate markers (operative time, longer pelvic dissection time, involved resection margins, conversion to open surgery, quality of TME, operative blood loss and anastomotic leak.

Studies that investigated either soft tissue data, bony data, or both were included.

Studies that did not include pelvimetric measurements were excluded from the review. Furthermore, studies that did not assess surgical difficulty were excluded from the analysis. Only studies published in English were included.

After removing duplicate articles, abstracts were reviewed for eligibility. Full texts of eligible articles were then screened using the inclusion criteria.

The search strategy has been summarized according to the PRISMA flowchart (Figure 1).

Figure 1 PRISMA flowchart of the search strategy.

Results

Thirty-seven studies were included in the analysis with a total of 5,028 patients identified. These studies were published from 2005, 2007–2011, 2014–2015, 2017–2023. Twenty-three papers were published in Asia, 11 were published in Europe, 2 in North America and 1 in Australia.

A majority of the patients underwent anterior resection (89%) for middle or low rectal cancers: open (25.8%), laparoscopic (61.3%) and robot-assisted (12.9%) procedures. Of these patients, 91% underwent low anterior resections and 9% underwent ultralow anterior resections. Other procedures performed include: Hartmann’s procedure (0.05%), abdominoperineal resection (APR) (4%), and intersphincteric resection (ISR) (6%).

Twenty-five studies performed pelvimetric assessments based on bony measurements alone (8-32). One study looked at only soft tissue pelvic measurements (33) and 11 studies assessed both bony and soft tissue measurements (34-44).

The surgical difficulty was measured using surrogate indicators of difficulty. The most commonly used indicators were operative time, used in 21 studies (8,11,12,18-22,24,25,27,29,31,34,37,38,40-44). Intra-operative blood loss, used in 11 studies (11,21,24,25,27,29,31,34,37,38,42). Involvement of surgical resection margins in 9 studies (11,13-15,17,21,23,33,39). TME quality was used in 7 studies (13,15-17,27,32,39). Length of post-operative stay was used in 7 studies (25,27,29,34,37,38,42). Anastomotic leak was used in 5 studies (8,11,26,28,32). Conversion to open surgery was in 5 studies (25,27,34,37,38).

Surgical difficulty scoring

Escal et al. described a conjugate score to assess surgical difficulty (38). Six variables were used: duration of surgery >300 min; conversion to open procedure; use of transanal dissection; post-operative stay >15 days; blood loss >200 mL; morbidity defined by (Clavien-Dindo grade II and III) (45). These variables were given points with a surgical difficulty grade ranging from 0–12 points (a score of ≥6 was defined as high risk of surgical difficulty).

Several other studies have used a modified version of the Escal criteria to define surgical difficulty in their studies (25,27,34,37).

IS

A smaller IS was defined as the narrowest distance between the ischial spines (Figure 2) and was found to be associated with higher difficulty in eight studies (13,14,20,21,25,28,34,37) (Table 1).

Figure 2 Axial CT of male patient (A) and female patient (B) with green arrows showing measured interspinous distance. CT, computed tomography.

Boyle and colleagues found that in female patients predicted to have a negative CRM pre-operatively, but had positive CRM post-operatively, they had a smaller IS distance (97.3 vs. 110.4 mm, P=0.031) (14).

Baik et al. reported that a shorter IS was related to an incomplete TME [relative risk (RR) 0.502; 95% confidence interval (CI): 0.269–0.936] (13).

Lee et al. found a smaller IS (<90 vs. ≥90 mm, P=0.002) to be associated with longer pelvic dissection times in 90 patients undergoing laparoscopic low anterior resection (20).

de’Angelis et al. demonstrated a relationship between a smaller IS distance and conversion to open surgery in 170 patients who underwent laparoscopic TME after neoadjuvant chemoradiotherapy [odds ratio (OR) 0.85, 95% CI: 0.74–0.97, P=0.018] (37).

In a cohort of 1,058 patients with rectal cancer who underwent both open and laparoscopic (87.2%) anterior resections, a smaller IS distance was associated with an increased risk of anastomotic leak (OR 0.96, 95% CI: 0.94–0.97, P=0.001) (28).

A shorter IS was reported to be associated with increased surgical difficulty in laparoscopic TME in three studies (21,25,34).

MFA

Five papers found an association between a higher MFA and increased surgical difficulty (34,35,38,40,44) (Table 2). The definitions of MFA varied in the studies. MFA was as the area of mesorectal fat at the level of the tip of the S5 on T2 MRI (38,40) (Figure 3) or the area of the mesorectal fat at the level of the tip of the ischial spines (34,35,44).

Figure 3 T2 axial MRI slices showing mesorectal fat area (shaded in blue) of a female patient (A) and male patient (B), measured at the level of S5. MRI, magnetic resonance imaging.

Three of the five papers associated a larger MFA with longer operative time. Yamaoka et al. found that a larger MFA (≥26.0 cm²) was associated with a significantly longer operative time of the pelvic phase in robotic-assisted laparoscopic TME (44). Huang et al. also found a relationship between larger MFA and longer surgical duration for robotic-assisted TME (β=0.331, P=0.003) in multivariate analysis (40). Nagai and colleagues (35) also found a larger MFA to be associated with longer operative time for robot assisted TME (P=0.045).

A larger MFA was found to be statistically associated with increased surgical difficulty in two studies (34,38).

PI

The PI measured in the anterior-posterior (AP) plane was defined as the distance between the superior aspect of the pubic symphysis to the sacral promontory measured in the midsagittal section (Figure 4).

Figure 4 Sagittal CT of female patient (A) and male patient (B) with green arrows showing measurement of pelvic inlet. CT, computed tomography.

A smaller PI was related to increased surgical difficulty in 9 studies (10,11,13,14,24,26,28,31,32) (Table 3).

Boyle and colleagues demonstrated that female patients predicted to have a negative CRM pre-operatively, but had positive CRM on pathology had a shorter PI (107 vs. 116.1 mm, P=0.017) (14).

Zhou et al. identified that a shorter AP PI was significantly associated with longer operative time in 60 patients who underwent open surgery anterior resection or APR for middle-low rectal cancers (31). Teng et al. (10) found that a smaller PI <11.0 cm was independently associated (OR 0.439, 95% CI: 0.240–0.804, P=0.008) with longer operative times in 214 patients who underwent laparoscopic anterior resections for middle and low rectal cancers.

Shimada et al. showed that the shape of the PI-measured using the ratio of the AP diameter and the transverse (T) diameter AP/T was an independent risk factor for extended operative time (P=0.036) (24).

Atasoy et al. demonstrated that a smaller PI was an independent risk factor for intraoperative blood loss in 125 patients who underwent open TME for middle and low rectal cancers (P=0.004) (11).

In a cohort of 117 patients who underwent an ISR, it was found that a smaller PI plane area was associated with an increased risk of anastomotic leak (OR 0.998, 95% CI: 0.997–0.999, P=0.012). They suggested that a narrow PI area (≤10,074 mm²) could predict anastomotic leakage with a sensitivity of 90% and specificity of 85.9% (26). Similarly, this was observed in another cohort of 1,058 anterior resections (28).

Finally, a smaller PI was shown to be associated with poorer quality TME specimens (13,32).

IT

IT (Figure 5) was defined as the widest distance between the ischial tuberosities (19,28,38).

Figure 5 Axial CT of female patient (A) and male patient (B) with green arrows showing measurement of IT distance. CT, computed tomography; IT, intertuberous.

Three studies associated a narrower IT with increased surgical difficulty (19,28,38) (Table 4).

Yu et al. (28) identified a narrower IT to be an independent risk factor (OR 0.97; 95% CI: 0.95–0.99) for anastomotic leak.

A narrower IT was reported to be associated with increased pelvic dissection time in laparoscopic TME (19).

Discussion

This systematic review has found that there is no standardized definition of “difficult pelvis” in rectal cancer resections. Various pelvimetry data such as a smaller IS distance, larger MFA, smaller PI and a narrow IT distance have been associated with an increased difficulty in TME surgery.

The pelvimetry data is paramount as the incidence of rectal cancers is expected to increase coupled with an increasing obesity endemic (46). The increased utility of TNT is likely to achieve complete clinical response in up to 30% of patients with locally advanced rectal cancer, but the remaining incomplete responders will eventually require TME (47). With these factors, pre-operative pelvimetric data from the staging imaging can be used to assess the surgical difficulty with no extra cost. In the era of TNT, there is potential to encounter more fibrosis in the TME dissection planes. The surgical approach can be planned accordingly. For example, in cases deemed difficult based on pelvimetric data, a combined laparoscopic and trans-anal TME can be utilized (48,49). These pelvimetric data can also be used for more selective robotic platform usage as currently the access to a robot remains limited in most centres.

A higher predicted risk of anastomotic leak from the pelvimetric data could assist in counselling patients pre-operatively of the need for a diverting ostomy. In cases predicted to have either a positive CRM or distant resection margin, the pelvimetric data may engender consideration of TNT over long-course chemoradiotherapy to potentially further downsize the tumour. Furthermore, in distal lower third rectal tumour, a decision can be made upfront for APR over ultralow anterior resection to reduce the risk of positive margins.

As the watch-and-wait approach has been incorporated into the clinical practice, the learning curve for rectal cancer resections becomes steeper due to reducing caseloads (50). Pelvimetry data can help to determine appropriate training cases for surgeons subspecializing in colorectal surgery. Depending on the anticipated difficulty of the case, the trainer can decide on the level of supervision (51,52). This can be translated into centres with dual-console robotic platforms where further supervision can be provided (53).

The surgical difficulty is often difficult to define even with a conjugate measure (38). This limits effective comparison between the studies. The most frequently used indicator of difficulty was operative time, used in 21 studies. Total operative time may not be an accurate surrogate measure of the “difficult pelvis”. Factors such as long adhesiolysis contribute to a longer total operative time while in fact, the pelvic phase of the operation may be significantly shorter. Only two studies specifically qualified the operative time into total time and pelvic dissection time (19,20). While several studies have reported the use of intra-operative blood loss as an indicator of difficulty, the source of the bleeding is not specified. A critique is that reported bleeding could have occurred at sites anatomically distant from the pelvis—i.e., bleeding that is unrelated to the “difficult pelvis”. The cut-off for volume of blood loss is often arbitrary as well. Post-operative indicators such as LOS are influenced by other factors other than surgical difficulty alone. Similarly, for anastomotic leak, it could be secondary to reasons such as the number of stapler firings for transection, the anastomosis configuration, perfusion of the anastomosis, presence of diverting ostomy and pre-operative radiotherapy.

Future studies should use a standardized outcome measure for comparison. The TME grade with CRM and distal resection margin are likely to be the most objective measure for surgical difficulty in rectal cancer resections.

Conclusions

The current literature on various pelvimetric data demonstrated a degree of correlation with the difficulty of surgical rectal dissection. Unfortunately, many of the outcome variables are subject to influence from external factors. The findings of this study call upon prospective studies with standardized outcome measures. Composite scores using objective pelvimetric measurements can be explored further, thereby reducing the reliance on surrogate indicators of difficulty.

Acknowledgments

Funding: None.

Footnote

Reporting Checklist: The authors have completed the PRISMA reporting checklist. Available at https://ales.amegroups.com/article/view/10.21037/ales-24-12/rc

Peer Review File: Available at https://ales.amegroups.com/article/view/10.21037/ales-24-12/prf

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://ales.amegroups.com/article/view/10.21037/ales-24-12/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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