High-resolution anorectal manometry for diagnosing obstructed defecation syndrome associated with moderate rectocele compared to healthy individuals

A rectocele in women is a hernia presenting itself as a bulge in the rectum wall to the side of the vagina, which may result in obstructed defecation syndrome (ODS) [1] due to a defect in the pelvic floor support structure or weakness in the function of the pelvic floor muscle. Consequently, patients have incomplete rectal emptying with or without a reduction in the number of bowel movements per week [2, 3].

Defecography is the first-line diagnostic method for assessing anorectal function and structural morphology [4]. It has revealed typical features of pelvic floor dysfunction, even in some asymptomatic individuals [5]. Our previous study showed differences in age and sex among healthy volunteers using three-dimensional high-resolution anorectal manometry (3D HRAM) [6]. Intrarectal pressure is related to age, body mass index (BMI), and parity [7], and the duration of sustained squeeze is shortened in multiparous females [8]. Age was also negatively correlated with balloon expulsion time (BET), whereas a higher BMI was associated with a higher maximum tolerated volume, longer BET, and greater length of the high-pressure anal zone (HPZ) in males than in females [9]. A study comparing the Eastern and Western literature found that the 3D HRAM parameters of healthy volunteers showed ethnic differences [10].

However, the accuracy of the diagnosis of defecation disorders using 3D HRAM has been questioned. Eighty-seven percent of healthy asymptomatic individuals and patients with dyssynergic defecation share similar 3D HRAM values [11]. The manometric parameters measured with the 3D HRAM probe cannot accurately predict prolonged BET [12], and normal anorectal manometry or BET results can occur in patients with dyssynergic defecation during defecography [13]. HRAM and magnetic resonance imaging explained only 36% of the variance in the bowel evacuation parameters, suggesting that these parameters did not fully capture the dynamic factors of the pelvic floor associated with successful defecation [14]. The clinical significance of normal and abnormal 3D HRAM values is unclear; however, when considering each functional parameter individually, individuals with parameter values outside the normal range may have no clinical symptoms, and patients with clinical problems may exhibit normal values. Given the enormous capacity of functional compensation, isolated dysfunction may not be clinically meaningful. Furthermore, the pathophysiology of most clinical diseases is multifactorial, and symptoms may appear only when multiple parameters are affected [15]. Therefore, no gold-standard diagnostic method exists for ODS [16].

Most studies have focused on the application of 3D HRAM in diagnosing dyssynergic defecation, which accounts for approximately 40% of ODS [17]. Few studies have explored the significance of 3D HRAM values in diagnosing ODS associated with moderate rectocele in women (MRW). Previous studies on normal 3D HRAM values in healthy volunteers stratified participants by sex, BMI, and age using different methods, and some studies did not stratify patients based on disease severity, which may have led to biased or opposite results [6, 9, 14]. More studies are urgently required to stratify patients according to age and disease severity to properly assess 3D HRAM accuracy in diagnosing ODS.

This study aimed to identify independent risk factors that influence the diagnostic value of the receiver operating characteristic (ROC) curve in the MRW and healthy female individual (HFI) groups by comparing the 3D HRAM parameters, which have practical clinical implications for the accurate diagnosis and stratified treatment of rectoceles.

In this study, 3D HRAM was used to assess the diagnostic value of age and disease severity stratification with respect to HFI and MRW. The biggest advantage of 3D HRAM is that it can be used for two-dimensional (2D) and 3D analysis. The color contour map can be used to understand the pressure curve more intuitively; the 3D map shows the blue low-pressure band of the characteristic areas of rectal defects in patients with MRW (Fig. 4). However, the accuracy of 3D HRAM diagnosis was affected by the technician’s level of operation, and the 3D HRAM operator in this study had 12 years of experience. Therefore, the pressure measurement parameters were normally distributed with a uniform variance, indicating that our parameters were reliable and usable.

In this study, a cutoff point method for age ≥50 years was adopted as in previous studies [8, 10, 24‐26]. Comparing the ≥ 50-year to <50-year subgroup, the maximum squeezing pressure was lower in the HFI group. Multivariate binary logistic regression analysis showed that age was an independent risk factor of MRW. In the HFI group, a negative correlation was found between age, maximum resting pressure, and maximum squeezing pressure, but not in the MRW group. Li et al. reported a negative correlation between age and the maximum resting, mean resting, and maximum squeezing pressures in the HFI group [6]. Noelting et al. reported that age >50 years was associated with lower resting anal pressure in the HFI group; however, age < 50 years was not associated with squeezing pressure, and younger females had a more negative rectal pressure differential than older females [23]. Coss-Adame et al. reported a significant reduction in resting and sustained squeeze pressures in women aged > 50 years [25]. The differences in these results may be related to the differences in age, parity, BMI, ethnicity, and grouping methods of the volunteers enrolled in the study.

The difference in these 3D HRAM parameters between the MRW and HFI groups in this study may be related to the prolapse of the rectal mucosa and fecal matter within the rectal thrust-forward congestion of the anus. RAIR sensitivity was lower than that of HFI, resulting in an increase in the maximum resting and mean resting pressures. To facilitate smooth defecation, the residual anal, intrarectal, and rectoanal pressure differential increased; simultaneously, the maximum squeezing pressure was increased to maintain continence. Prichard et al. reported that intrarectal pressure, perineal descent scores during excretion, and dilated anal canals were associated with rectoceles > 3 cm [14]. This is consistent with our findings: age was not associated with MRW. However, this study reported that the age of the HFI group was negatively correlated with the maximum resting and squeezing pressures. Patients with abnormal rectal structure have lower median intrarectal pressure and a negative median rectal gradient during excretion [14]; however, a BET subgroup analysis was not performed. The mean resting pressure is the pressure at which the anorectal resting level reflects the function of the internal anal sphincter, and a high anal resting pressure may indicate smooth or striated muscle spasms [14]. The maximum squeezing pressure and duration of sustained squeeze reflect the function of the external anal sphincter and pelvic floor muscles, while the duration of sustained squeeze is a manifestation of the endurance of the slow muscle, with females squeezing less than males and older people squeezing less than younger people [6‐9, 24, 25]. Coss-Adame et al. reported a significant reduction in rest and duration of sustained contractions in females aged > 50 years [25]. Furthermore, differences in residual anal, intrarectal, and anorectal pressures reflect the propulsive force exerted on the anorectum during simulated defecation.

The RAIR is an essential component of normal defecation and is characterized by decreased intrarectal pressure during rectal balloon distention. RAIR is characterized by relaxation along the anteroposterior axis, length of the canal, and differences with the vector, with the largest changes occurring at the internal anal sphincter level [26], and the magnitude and duration of RAIR depend on the rate and volume of rectal dilation [27]. A non-HRAM study detected RAIR deletions with a diagnostic utility of 91% and a specificity of 94% [28]. Neural pathways and reflex mechanisms in the muscles of the colon, rectum, anal sphincter, and pelvic floor are involved in defecation and continence [29]. The defecation receptor is located in the rectum, and RAIR reflects the sensitivity of the rectal defecation receptor in the brain and the reflex arc of rectal defecation [30]. When RAIR is initiated, a large amount of rectal content enters the lower rectum, and the sympathetically driven defecation reflex begins unless inhibition is consciously felt [31]. Multivariate binary logistic regression analysis showed that age and RAIR were independent factors affecting the disease.

The Youden index, also known as the correct index, refers to the sum of sensitivity and specificity minus one; thus, the range of index values is 0–1, and the larger the Youden index, the better the authenticity. The ROC curve demonstrated that the 3D HRAM parameters exhibited a higher diagnostic value for age, urge to defecate, and rectoanal pressure differential in the MRW group, as evidenced by the superior Youden index. Because the Youden index is low, 3D HRAM cannot be used as the gold standard for diagnosing MRW.

Our study was a prospective non-randomized controlled trial with potential weaknesses, including a small sample size after subgroup analysis. Moreover, we did not have data on the number of patients with hand-assisted bowel movements. The prevalence of sphincter defects was higher in females who delivered vaginally and increased with parity [32]. However, the number of females who delivered vaginally and the normal and abnormal BET for both groups were not statistically recorded. Furthermore, more randomized controlled trials are needed to investigate the effect of the simulated defecation squatting and left lateral decubitus positions on 3D HRAM parameters. A control group for MRI defecography and 3D ultrasound is required to determine the diagnostic value of 3D HRAM for MRW.

In this study, age and RAIR were screened as independent risk factors for MRW using 3D HRAM parameters from binary logistic regression analysis. Compared to the HFI group, the ROC curve of the 3D HRAM parameters suggests that age, urge to defecate, and rectoanal pressure differential in the MRW group have significant diagnostic value. Because the Youden index was lower, 3D HRAM cannot be considered a gold standard for diagnosing MRW. Our findings are of practical interest for the accurate diagnosis and stratified treatment of rectocele.