Hypothesis / aims of study
Fecal incontinence (FI), defined as the complaint of involuntary loss of feces, has two subtypes: fecal urgency incontinence (FUI), the complaint of the loss of feces associated with urgency, and passive fecal leakage (PFL), involuntary soiling of liquid or solid stool without sensation or warning or difficulty wiping clean [1]. Fecal continence is multifactorial, depending on an adequate rectal reservoir, adequate fecal sensation, stool consistency, and a functioning integral sphincter mechanism. Incontinence occurs when one or more of these mechanisms are compromised beyond compensation by any of the other factors. 3D endovaginal and endoanal ultrasound have an established role in evaluation of FI [2]. The current study aimed to compare the shape and function of the pelvic floor, the rectum and the anal sphincter complex detected by pelvic exam and 3D endoluminal and 2D posterior compartment dynamic ultrasound in women with FUI versus PFL.
Study design, materials and methods
This was a retrospective observational study and received approval of the Institutional Review Board. Women who presented for evaluation of FI to our tertiary center, between January 2018 and February 2020, were recruited to the study. The presence of FI symptoms was documented if they answered “yes” to questions 9, 10, or 13 on PFDI-20 questionnaire. During the visit, patients underwent a complete interview including: a detailed review of FI pattern and Bristol stool chart for stool type; pelvic exam including POP-Q and rectal exam; and 3D endovaginal pelvic floor ultrasound, 3D endoanal ultrasound and 2D posterior compartment dynamic ultrasound. The imaging was performed in the office with patient in lithotomy position.
Patients were categorized to three groups: FUI-dominant FI, PFL-dominant FI, and both.
A dominant pattern was established if the patient reported at least twice the frequency of one pattern over the other. The patient was categorized as “both” if neither pattern was dominant.
3D Endovaginal ultrasound measurements: The levator muscle was divided in to three subgroups (3): the puboperinealis/puboanalis (PA), puborectalis (PR), and iliococcygeus (IC). Subgroups were evaluated and were scored (0=no defect, 1=minimal defect with < 50% muscle loss, 2=major defect with >50% muscle loss, 3=total absence of the muscle) on each side based on thickness and detachment from the pubic bone. Each muscle score ranged from 0, indicating no defects, to a maximum score of 3, indicating total muscle absence. Minimal levator hiatus, anorectal angle and rectal area at the level of anorectal junction were measured.
3D endoanal ultrasound measurements: The external anal sphincter (EAS) was visualized and, if present, defects were detected. The appearance of an EAS defect is a break in the circumferential integrity of the mixed hyperechoic band. A defect can have either a hypoechoic or hyperechoic pattern. This corresponds to replacement of the normal striated muscle with granulation tissue and fibrosis.
Defects of the internal anal sphincter (IAS) are easily recognized given the prominent appearance of the IAS in the mid-anal canal. They appear as hyperechoic breaks in the normally hypoechoic ring.
2D dynamic posterior compartment ultrasound: The distance between the posterior cul-de-sac and anorectal junction (“rectovaginal septum length”) was measured both at rest and during Valsalva in the mid-sagittal plane, Figure1. “Compression ratio” was calculated as a means to quantify the relative change in length of the rectovaginal septum (RVS), in other words the degree of hypermobility / sliding rectum, and was expressed as a percentage.
Statistics: Baseline symptoms, physical examination and 3D-pelvic ultrasound were performed and compared using chi-squared, Fisher’s exact test and ANOVA. A sample size of 121 women were needed to detect a 30% difference in pelvic floor defects between the groups with 90% power and p<0.05.
Results
145 patients were included in the analysis; 57 categorized as FUI-dominant FI, 69 PFL-dominant FI, and 19 categorized as “both”. There were not statically significant differences in the demographic values except for age. The urge-predominant patients were significantly younger than the rest predominant (65.58 ± 12.85 vs 70.32 ± 12.71, p 0.040). While comparing bowel habit and symptoms of obstructed defecation, patient with FUI-dominant FI had more frequent bowel movements (15.5 +/- 13.0/week vs. 10.9 +/- 7.6 /week, p=0.039) and were more likely to have loose stools (12.5% vs. 4.3%, p=0.01). The physical exam findings including POP-Q, levator ani muscle tone and anal sphincter rest and squeeze tone were similar among the groups. Table 1 has summarized the comparison of ultrasound parameters and demonstrated the only statistically significant difference being in rectal compression ratio between urge FI and PFL (28.1 +/- 26.6 vs. 16.6 +/- 21.19, p=0.01).
Interpretation of results
Patients with FUI-dominant FI had more frequent bowel movement and a higher prevalence of loose stool compared with patients with PFL-dominant FI. These findings are consistent with existing studies.
Amongst the ultrasound parameters, patients with FUI had higher rectal compression ratio during Valsalva. The higher rectal compression ratio is associated with presence of rectal intussusception, rectal prolapse and enterocele. This suggests that there may be a dynamic anatomic component to the symptom of FUI.