Sequential assessment of bowel function and anorectal physiology after anterior resection for cancer: a prospective cohort study

The aim of this study was to investigate changes in bowel function and anorectal physiology (ARP) after anterior resection for colorectal cancer.


INTRODUC TI ON
Colorectal cancer survival in the UK has more than doubled in the last 40 years from 22% to 57% (10-year age-standardized survival) [1]. Improvements in preoperative imaging, surgical technique and chemoradiotherapy have contributed to this [2][3][4]. Patients expect not only to be cured of bowel cancer but also to have good functional outcome in terms of bowel, bladder and sexual function. Unfortunately, a significant proportion of patients experience unwelcome bowel symptoms that affect their quality of life. This constellation of symptoms has been termed low anterior resection syndrome (LARS) and affects 40% of patients who have sphincter-preserving surgery [5]. A recent international consensus definition describes eight symptoms (e.g. frequency, urgency, incontinence) and consequences (e.g. toilet dependence, preoccupation with bowel function) and recommends that the diagnosis of LARS is dependent on the patient experiencing at least one symptom and one consequence [6]. Importantly, it has been shown that LARS does not only affect patients who have low anterior resection, with more than 20% of patients with sigmoid cancer reporting major LARS after surgery [7]. Risk factors for LARS include neoadjuvant radiotherapy [8,9], low rectal tumour [9][10][11] and a temporary defunctioning stoma [12,13].
The pathophysiology of LARS has not been fully elucidated and is likely to be multifactorial. It is thought that a combination of altered colonic transit [14], neorectal denervation [15] and internal anal sphincter injury [16] may contribute. These pathophysiological processes may manifest as changes in anorectal physiology (ARP).
The objectives of the current study were: (i) to document incontinence and stool frequency after anterior resection for colorectal cancer; (ii) to assess postoperative changes in ARP; (iii) to determine the effect of neoadjuvant radiotherapy, anastomotic height, defunctioning stoma and operative approach; and (iv) to correlate incontinence and stool frequency with ARP.

ME THOD
This study was given ethical approval by the Southampton and Anal incontinence was evaluated using the Cleveland Clinic Incontinence (CCI) score [22] and stool frequency as part of the MSKCC BFI questionnaire [23]. Questionnaires were completed at the following time points: immediately before surgery (T 0 ) and 3 months (T 3 ), 6 months (T 6 ), 9 months (T 9 ) and 12 months (T 12 ) after surgery (or restoration of intestinal continuity).
Anorectal physiology was recorded at T 0 , T 3 and T 12 using a stationary pull-through technique with a four-channel water-perfused Medtronic catheter. A computerized system (Polygam Lower GI, Synectics Medical, Stockholm, Sweden) was used for data acquisition. Resting pressure and squeeze increment were measured from five stations at 1 cm intervals from +6 to +1 cm above the anal verge.
Measurement of pressure (resting and squeeze increment) at each station was an average of the pressure recorded by the four channels in the catheter tip. Maximum tolerable rectal volume was assessed by inflating a balloon with water at body temperature inside the rectum at 5 cm from the anal verge. ARP parameters included maximum resting and squeeze pressures, volume at first urge and maximum tolerable rectal volume.
Anal sphincter dimensions were measured at T 0 and T 12 , using a BK medical endoanal ultrasound (EAS) probe with the patient in the left lateral position.
Baseline (T 0 ) questionnaires, ARP and EAS were completed before commencement of neoadjuvant radiotherapy wherever possible.

Statistics
Graphpad Prism 9 was used for all statistical analyses. Data were tested for normality using the Kolmogorov-Smirnov test.
Nonparametric variables were compared using Wilcoxon (paired) or Mann-Whitney (unpaired) tests, as appropriate. Parametric variables were compared using paired or unpaired t-tests. The strength of correlations was assessed by the Spearman rank method. Categorical variables were compared by 2 × 2 contingency tables (Fisher's exact test). Two-tailed tests were used where applicable, with an alpha significance level of 0.05. Nonparametric data are represented as median ± interquartile range (IQR) and parametric data as mean ± SEM, unless otherwise stated.

What does this paper add to the literature?
This large prospective study documents the link between anorectal physiology and incontinence/stool frequency in the 12 months following anterior resection for colorectal cancer, with subgroup analysis of neoadjuvant radiotherapy, anastomotic height, defunctioning stoma and operative approach.

Incontinence and stool frequency in the first year after anterior resection
There was a significant increase in the proportion of patients with incontinence (CCI > 0) from T 3 onwards ( Table 2). The median CCI score for the entire cohort increased at T 3 (p = 0.0125), T 6 (p = 0.0213) and T 9 (p = 0.0024) compared with baseline but not significantly at T 12 ( Figure 2A). Patients who received neoadjuvant radiotherapy had no difference in baseline CCI score but significantly higher CCI scores at T 3 (p = 0.0212) and T 6 (p = 0.0295). However, these differences were not sustained at T 9 and T 12 ( Figure 2B). Patients with a lower anastomosis (below the peritoneal reflection) had no difference in CCI scores at baseline but significantly higher CCI scores at T 3 (p = 0.0110) although not thereafter ( Figure 2C). Defunctioning stoma ( Figure 2D) and operative approach ( Figure 2E) had no effect on the CCI score at any time point.
There was no change in stool frequency in the entire cohort at any time point ( Figure 3A). Patients who had neoadjuvant radiotherapy had no difference in stool frequency at baseline but an increased number of stools at T 3 (p = 0.0038), T 6 (p = 0.0237) and T 12 (p = 0.0403; Figure 3B). The increase at T 9 did not quite reach significance (p = 0.0615). Patients with a lower anastomosis had no difference in stool frequency at baseline but an increased number of stools at T 3 (p = 0.0129) and T 6 (p = 0.0124), although not thereafter ( Figure 3C). Patients who had a defunctioning stoma had no difference in stool frequency preoperatively but an increased number of stools at T 3 (p = 0.0009), T 6 (p = 0.0155) and T 12 (p = 0.0013; Figure 3D). Patients who had open surgery had a higher number of stools preoperatively (p = 0.0137) and at T 12 (p = 0.0354) but not in the intervening period ( Figure 3E).

ARP in the first year after anterior resection (entire cohort)
To objectively measure changes in bowel function after anterior resection, ARP was conducted at baseline, T 3 and T 12 for the entire cohort. Maximum resting pressure decreased by 13.5 mmHg at T 3 (p < 0.0001) and 16.5 mmHg at T 12 (p < 0.0001), compared with baseline ( Figure 4A). Volume at first urge reduced by 16.4 ml (p = 0.0249) and 15.7 ml (p = 0.0198; Figure 4B). Maximum rectal tolerance reduced by 36.9 ml (p < 0.0001) and 18.9 ml (p = 0.0125; Figure 4C).
Maximum squeeze pressure was not significantly changed at T 3 or T 12 ( Figure 4D) and was, therefore, not examined further.

Effect of neoadjuvant radiotherapy, height of anastomosis, defunctioning stoma and operative approach on ARP
The cohort was then grouped by neoadjuvant radiotherapy

Correlation between anorectal physiology and CCI score
Having documented a change in incontinence/stool frequency and ARP in the 12 months following anterior resection, the association  Figure 6A-F). Selected ARP parameters which changed significantly after anterior resection were plotted against CCI score or stool frequency at 12 months. Resting pressure did not correlate with CCI (p = 0.2560; Figure 6A) or stool frequency (p = 0.5977; Figure 6D).
First urge (p = 0.0756) seemed to be negatively correlated with CCI but did not reach significance ( Figure 6B), whereas it correlated significantly with stool frequency (p = 0.0453; Figure 6E). Maximum tolerance showed a significant negative correlation with CCI at 12 months (p = 0.0297; Figure 6C) and a negative correlation with stool frequency, which did not reach significance (p = 0.0942; Figure 6F).

Changes in anal sphincter dimensions after anterior resection
Endoanal ultrasound was used to measure anal sphincter dimensions in 48 patients (Table 3). Tumour height, neoadjuvant radiotherapy and defunctioning stoma rates in this group were comparable across the entire cohort (Table 3A). The length of the anterior internal anal sphincter reduced by 1.7 mm postoperatively (p = 0.032). There were no significant changes in any of the other parameters (Table 3b).

DISCUSS ION AND CON CLUS IONS
This is the largest prospective study to sequentially document incontinence and stool frequency together with measurements of ARP after anterior resection for colorectal cancer. The key findings were as follows: (i) faecal incontinence increased postoperatively and was greater in patients who had neoadjuvant radiotherapy and a lower anastomosis; (ii) stool frequency did not change postoperatively but was greater in patients who had neoadjuvant radiotherapy, a lower anastomosis and a temporary defunctioning stoma; (iii) resting anal tone, rectal sensation and capacity decreased postoperatively and were negatively influenced by neoadjuvant radiotherapy, lower anastomosis and defunctioning stoma; (iv) rectal capacity correlated with CCI score and rectal sensation with stool frequency; and (v) length of the anterior internal anal sphincter decreased postoperatively.
The present study confirms previous reports that anal incontinence deteriorates after rectal resection but then improves in the first 12 months after surgery [24]. This is relevant because a window and frequency-dominant LARS, with radiotherapy identified as a risk factor for incontinence and low tumours for frequency [25].
Furthermore, the effect of radiotherapy on incontinence in our study was surprisingly short-lived (3 months). This may represent an initial improvement in acute radiation proctitis [26]. However, studies have shown that patients who had radiotherapy can have incontinence that persists for several years after surgery [27]. This is attributed to the establishment of chronic proctitis or radiation-induced fibrosis.
Unfortunately, it was not possible in our study to re-evaluate these patients for longer-term effects of radiotherapy. Equally, the numbers of patients having long-course and short-course radiotherapy were not sufficient to perform subgroup analysis, although it has been shown previously that this does not influence LARS symptoms or quality of life [28][29][30].
Similarly, the effect of lower anastomosis on incontinence was not demonstrated beyond 6 months in the present study. The compliance of the neorectum improves after a period of remodelling [31], which may partly explain this. However, large cross-sectional studies with follow-up for several years after surgery have shown long-lasting effects of low anastomosis on bowel-related quality of life [30].
It should also be mentioned that ARP may be altered, or measurements impaired, by fibrosis and scar tissue following a rectal anastomosis, with the balloon not inflating as it would in a surgery-naive patient. This should be considered when interpreting results, as it may influence the relationship between ARP and clinical symptoms.
In keeping with previous studies [17,18,20], we showed a sustained reduction in resting anal tone in the first year after surgery.
This corresponded with a decrease in length of the internal anal sphincter. Damage to sympathetic nerves, which course in the intersphincteric space and supply the internal anal sphincter, may be responsible for LARS symptoms in low anterior resection [32].
However, this mechanism would not necessarily account for the symptoms experienced by patients having high anterior resection [7]. With regard to LARS in patients having a sigmoid resection, Elfeki et al. [33] identified 12 bowel symptoms ('excessive straining, fragmentation, bloating, nocturnal defaecation, bowel false alarm, liquid stool incontinence, incomplete evacuation and sense of outlet obstruction') which include incontinence but not stool frequency, highlighting that patterns of LARS may be different after surgery for sigmoid and rectal cancer. Nonetheless, it has been shown that the internal anal sphincter can be damaged by insertion of the transanal stapling device and this should also be considered in the pathophysiology of LARS in both high and low anterior resection [34]. Of note, all patients in the present study had a stapled transanal anastomosis.
In terms of operative approach, the literature to date is sparse about its impact on LARS. Kang et al. [35] showed that fewer patients having laparoscopic low anterior resection had 'defecatory problems' compared with those having open surgery. However, that study was restricted to patients with mid to low cT3 tumours. In contrast, Andersson et al. [36] showed no difference in health-related quality of life between laparoscopic and open surgery groups in their analysis of the COLOR II trial. In the present study, we showed that at 12-months after surgery, stool frequency but not CCI score was lower in patients having laparoscopic surgery. In fact, stool frequency was lower at baseline in the laparoscopic group, suggesting that more-  Rather unsurprisingly, preoperative ARP predicts postoperative ARP [37]. However, pre-or postoperative ARP does not seem to predict LARS and does not feature in the POLARS nomogram [38].
In this study, not all ARP parameters correlated with CCI score and stool frequency and resting anal pressure did not correlate with either. This may reflect the limitation of using individual LARS symptoms or that multiple continence mechanisms are disrupted after anterior resection.
In terms of generalizability, the findings presented here are from a sample of patients who represent a typical urban Western European population, where management of colorectal cancer meets nationally recommended guidelines [39]. CCI scores, stool frequency and ARP parameters are in line with previous studies [17,19]. However, one of the main limitations is that there has been a significant delay from study completion to data submission. Nonetheless, the sequential recording of ARP measurements after anterior resection, coupled with incontinence and stool frequency data, has not been duplicated in this number of patients. More importantly, there is an ethical duty to the patients who participated and the colorectal research community to present this data, in line with the AllTrials campaign [40]. Nonetheless, our understanding of LARS has changed significantly in this time. In particular, the study pre-dated the LARS score [41]. As such, the present study focuses on faecal incontinence and stool frequency, as two of the most frequent LARS symptoms [42].
Another point for discussion is the measurement of anastomotic height. This was inferred from the histopathological specimen and whether or not it included the peritoneal reflection. Clearly, this method is unable to distinguish between an anastomosis at 3 cm and 6 cm for example, which may result in different functional symptoms and altered rectal sensation and capacity. The original intention was to perform sigmoidoscopy immediately after the anastomosis was fashioned, to determine an accurate anastomotic height, as studies have shown a direct link between the level of anastomosis and functional outcome [12,43]. However, several surgeons involved in the study did not agree to this. An alternative was to use tumour height as a proxy, but distal resection margins vary from procedure to procedure and therefore this was not used. It should also be noted that in this study, which included patients having high and low anterior resections (sigmoid and rectal tumours), radiotherapy, anastomotic height and defunctioning stomas were likely to be confounding factors (as radiation is not used for sigmoid tumours and patients with higher anastomoses are less likely to be defunctioned). Although not our main objective here, future studies aiming to predict LARS based on risk factors should consider stratified or multivariable analyses.
In terms of defunctioning stomas, Vogel and colleagues recently published a systematic review suggesting that increased time to stoma closure was a risk factor for major LARS, with a mean difference of 2.4 months between 'major LARS' and 'no LARS' groups [13]. Time to stoma closure in the present study fell within a narrow range (IQR 3-7 months) but was clearly greater than this threshold, highlighting a potential source of bias.
Questionnaire completion rates ranged between 80% and 100%. At 6 and 9 months, postal questionnaires were used, which explains the lower completion at these time points. ARP rates were 76%-100% and EAS 44%-54%. Considering that ARP and EAS are invasive and do not form part of routine surgical or oncological follow-up, these rates are understandable. However, certain groups of patients may have been more or less likely to attend study follow-up due to the severity of their symptoms, oncological outcome or satisfaction with treatment, which is another potential source of bias.
Another consideration is the use of the CCI/ Wexner score to measure incontinence symptoms. This is a quick, easy-to-complete and easy-to-score tool, which has been validated and used extensively since 1993 [22]. However, it uses vague quantifiers (e.g. 'sometimes'), which means that severity is influenced by patients' personal experience. In addition, incontinence to solid, liquid or gas, use of pads and effect on lifestyle are given equal weighting in determining severity [44]. Nonetheless, it has been shown by Vaizey et al. [45] that CCI score correlates well with the clinical impression of incontinence. A bowel diary could have been used to supplement this for better discrimination of episodes of incontinence per day or week [46].
The primary outcome measures of this study were incontinence/ stool frequency and ARP. However, as already discussed, LARS encompasses a number of symptoms and effects which include, but are not limited to, incontinence and frequency [6]. Quality of life after rectal resection is an equally important set of outcomes and a number of tools have been employed to assess these, including global quality of life assessment tools (e.g. EORTC QLQ C30) and the faecal incontinence quality of life (FIQOL) instrument [30,47]. Quality of life has repeatedly been shown to correlate with LARS symptoms [48,49] and future studies should include quality of life assessment as standard.
Overall, this study highlights patterns of bowel dysfunction and changes in ARP after anterior resection with respect to specific risk factors (radiotherapy, anastomotic height, stoma and operative approach). Our hope is that these prospectively collected data, from a significant number of patients will add to the body of literature which informs clinicians and patients about the functional effects of major rectal resection.

ACK N OWLED G EM ENTS
RB is an NIHR funded Clinical Lecturer.

CO N FLI C T O F I NTE R E S T S
The authors report no conflicts of interest.

AUTH O R CO NTR I B UTI O N S
KPN and SAP conceptualized the study. SAP collected all data with help from SG. RB, SAP and SH analyzed the data. RB, SAP and KPN wrote the manuscript with critical review by CR, TCD, HY, JSK, ATK, AHM, NEB and PHN.KPN supervised the study.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.