Rectal intussusception (RI) is often seen in the setting of pelvic relaxation. However, mechanisms are not clear and RI can occur independent of pelvic relaxation. Aging is the biggest risk factor for pelvic relaxation and pelvic organ prolapse. Dynamic MR Defecography (MRD) allows evaluation of functional and structural pelvic floor disorders.
We Hypothesize that there is a correlation between rising grades of rectal intussusception (RI) and grades of uterovaginal and bladder descent associated with increasing pelvic floor relaxation and independent of age. 
The primary aim of our study was to assess the correlation between rising grades of RI with measures of pelvic floor descent in MRD. Our secondary aims were the correlation between severity of RI and 1) symptoms of fecal incontinence and obstructive defecation and 2) anorectal pressure profile from High Resolution Anorectal Manometry (HR-ARM).

We performed a retrospective analysis of a prospectively maintained registry of patients seen at our tertiary referral academic center. Symptoms were assessed using Cleveland Clinic/Wexner Fecal Incontinence questionnaire (CCFI), and the Obstructed Defecation Syndrome (ODS) questionnaire. All patients underwent MRD and HR-ARM as part of their clinical evaluations. Pelvic floor laxity was measured using the pubococcygeal reference line. The H line was drawn from the inferior margin of the pubic symphysis to the posterior aspect of the anorectal junction and M line was drawn perpendicularly from pubococcygeal line to the posterior end of the H line. Bladder and uterovaginal descent were measured based on descent below the pubococcygeal line. Rectal prolapse was graded using the Oxford classification. Patients were grouped based on Oxford grade 0 vs 1-2 vs 3 vs 4-5. Data was analyzed using Fisher exact test or chi- squared test in univariate analysis. Spearman rank correlation was used with partial and semipartial correlation for covariate adjustment.

A total of 238 women were included with 90(38%) no MRD findings of RI, 43(18%) Oxford grade 1-2, 49(20%) Oxford grade 3 and 56(24%) Oxford grade 4-5. There was a significant correlation between age (not BMI) and grades of RI in women, r: 0.140, P: 0.029. Women with higher grades of RI were more likely to have a history of vaginal delivery (P: 0.043) or pelvic surgery (P: 0.035). Despite comparable scores for obstructive defecation (ODS) , severity of fecal incontinence based on CCFI score, correlated with rising grades of RI, r:0.184, P: 0.007. 
HR-ARM showed higher grades of RI correlated with lower anal tone, r: -0.210, P: 0.001 and lower squeeze pressures, r: -0.153, P: 0.018. However these correlations didn’t persist after adjustment for age and BMI. There was no association between RI grades and rectal sensory thresholds. Women with higher RI grades were more likely to pass the rectal balloon within 60 seconds (P:0.005). 
RI grades correlated with measures of MRD pelvic floor relaxation including resting M (r: 0.191, P:0.003 and H (r: 0.210, P:0.001) lines, defecation M (r: 0.397, P:0.000) and H (r: 0.411, P:0.000) lines and only defecation (not resting or Kegel) anorectal angle (r: 0.252, P:0.000). When adjusted for BMI and age correlation remained significant with defecation M (P:0.000) and H (P:0.000) lines and resting H line (P:0.000). Interestingly there was also significant correlation with Kegel (P:0.008) as well as defecation anorectal angle(P:0.000). Correlation between RI grades and levator hiatus width (P:0.047) didn’t remain significant after correction for age and BMI (P:0.466). 
Women with higher grades of RI were more likely to have urethral hypermobility (P: 0.000). The grades of rectocele were comparable among patients with various degrees of RI but retaining rectocele was seen less commonly in women with high grades of RI (P: 0.030). Herniation at the level of sigmoidocele (P:0.004), enterocele (P:0.001), and, peritoneocele (P:0.000) were all significantly more common among women with higher grades of RI. 
MRD showed a significant correlation between rising grades of RI and rising grades of uterovaginal and bladder descent (P:0.000 for both). These correlations were independent of age and BMI.

We show that rising RI grades, observed in MRD in women, correlates with increasing age and is associated with worsening symptoms of fecal incontinence. There is no correlation between severity of obstructive defecation symptoms and RI grades. Also rising RI grades correlated with measures of pelvic floor relaxation including uterovaginal and bladder descent and intestinal herniation, independent of age and BMI.  When correlated with anorectal function, deterioration of anal sphincter function with rising grades of RI appeared to be affected by aging rather than rising grades of RI.

The pathophysiology of RI appears to be associated with pelvic floor relaxation and independent of age.

Continence 2S2 (2022) 100374
DOI: 10.1016/j.cont.2022.100374