Study population
This was a retrospective study performed at University Medical Center Groningen (UMCG), the Netherlands. We selected patients who had been referred to the Anorectal Physiology Laboratory Groningen for anorectal physiology tests and who underwent dynamic MR defecography between 2015 and 2021 to assess severe defecation disorders.
Criteria for exclusion were the male sex on account of the well-known anatomic differences between the male and female pelvic floors (n = 2), severe artifacts at MR that hampered adequate image evaluation (n = 1), spina bifida (n = 1), previous pelvic floor surgery (n = 13), sacral nerve stimulation potentially influencing anal function (n = 1), and a time interval between MR and manometry of more than 12 months (n = 10). Information regarding patients’ medical histories was collected from the electronic patient files.
Data collection
We used the Groningen Defecation and Fecal Continence Questionnaire (DeFeC), which was previously validated in a Dutch cohort, to evaluate anorectal symptoms, including constipation and fecal incontinence severity16. This questionnaire contains questions on constipation-related symptoms, including straining, hard stools, defecation blockage, manual defecation, as well as fecal incontinence-related symptoms, including soiling incontinence, liquid incontinence, solid incontinence, and urge incontinence.
We used the questionnaire to diagnose constipation and fecal incontinence based on the Rome IV criteria 16 and quantified their severity by assigning a Agachan constipation score,17 and a Wexner incontinence score18.
This study was performed in accordance with all applicable ethical standards and approved by our local medical ethical committee (METc 2019/252).
Dynamic magnetic resonance defecography
Dynamic MR defecography provides anatomic information on the pelvic floor during each defecation phase. This information can be important in patients with defecation disorders. More specifically, the H and M lines are most important in patients with defecation disorders.
Our dynamic MR defecography protocol was identical to the protocol proposed in the literature15. We performed all MR examinations with a 1.5T scanner (Siemens, Erlangen, Germany).
The H line is defined as the distance between the inferior aspect of the pubic symphysis and the posterior aspect of the anorectal junction15. The M line is the perpendicular distance between the posterior aspect of the anorectal junction and the pubococcygeal line15. The H and M lines were measured during rest, squeezing, and the defecation phases.
Anorectal physiology tests
Anorectal physiology tests provide information on pathophysiological factors underlying defecation disorders.
We performed the anorectal physiology tests using solar gastrointestinal high resolution manometry equipment (Laborie/Medical Measurement Systems, Enschede, the Netherlands, Version 9.6), as described previously19.
To determine anorectal physiology with manometry, we used the anorectal pressure profile, balloon retention (BRT), and defecometry tests. The anorectal pressure profile and BRT tests were described previously by Jonker and colleagues19. The defecometry test was previously described by Meinds and colleagues20.
Briefly, during the anorectal pressure profile test, we insert a Laborie/Unisensor K12981 solid-state (Boston type) circumferential catheter (Laborie, Portsmouth, NH, USA) into the rectum and fix it to the patient’s buttocks. The catheter measured resting and squeezing pressure at the level of the anal sphincter and puborectal muscle, respectively.
The BRT test started with introducing two catheters into the anorectum. A Laborie/Unisensor K12981 catheter was inserted into the rectum to measure anal sphincter pressure and puborectal pressure and fix it to the patient’s buttocks. Subsequently, a second catheter (Laborie/Unisensor K14204) was inserted with a nonlatex balloon at the tip to mimic solid stool into the rectum but this one was not fixed. The balloon at the tip was progressively filled with water at body temperature until the maximal tolerable volume.
The defecometry test began after the rectal balloon was emptied at the end of the balloon retention test. We gradually increased the volume of water until the patient was able to expel the balloon. The pressures at the level of the rectum, the puborectal muscle, and anal sphincter were measured just before defecation. Dyssynergic defecation during the defecometry test was determined based on the criteria proposed by Rao and collegues1.
Anal electrical sensitivity test
We performed the anal canal sensitivity test as described by Roe and collegues21 to reflect the pudendal nerve function14. We measured the anal electrical sensory threshold with a bipolar ring electrode mounted on a Foley catheter with length markings. The electrode was connected to a constant current stimulator that delivers electrical stimulation of 5 Hz with a duration of 100 µs. The intensity was increased gradually from 0 mA with a maximum of 25 mA until the patient felt the electricity2. The catheters could be moved to adjust the position of the electrode to levels of 1 cm from the anal verge.
Statistical analysis
All statistical analyses were performed using IBM SPSS Statistics, Version 23.0 (IBM Corp, Armonk, NY, USA). Continuous variables were reported as means ± standard deviations. Associations between two continuous variables were calculated by Spearman rank correlation or Pearson correlation coefficient depending on the normality of data. Normality was tested using Q-Q plots. A p value of < 0.05 was considered statistically significant. Figures were generated using GraphPad Prism 8.2.0 (GraphPad Software Inc, San Diego, CA, USA).