Does perineal body thickness affect fecal incontinence in multiparous patients?
It remains to be established whether obstetric trauma after two or more vaginal deliveries is a risk factor for developing incontinence later in life. Although the risk of new injury and defecatory symptoms occurring in subsequent normal deliveries is small (4%), 42% of asymptomatic women who have a pre-existing occult defect may develop impaired continence following a subsequent vaginal delivery, within 2 months of this delivery.  This impaired continence could be the result of a change in diet and bowel habits, ageing, anorectal surgery, haemorrhoids or irritable bowel syndrome.
Anatomically, in women, the perineal body separates the anal canal from the urogenital diaphragm in the median plane where the deep bulbospongiosus and superficial transverse perineal muscles meet the external anal sphincter (EAS). [3,4] The presence of a considerably bulky, tensile perineal body can be confirmed by the presence of a normal anal sphincter complex. A PBT of [less than or equal to] 10 mm or less is considered abnormal, according to the endosonographic perineal body measurement described by Zetterstrom et al. 
Anal endosonography is the gold standard in imaging the sphincters, and has superseded conventional electromyography mapping in the diagnosis of anal sphincter defects.  Endoanal ultrasound (EAUS) has revolutionised our understanding of the pathophysiology of faecal incontinence. Since its invention by Low and Bartram in 1989,  EAUS has been found to be superior to other diagnostic tools, with 100% sensitivity in detecting sphincter defects.  At the proximal anal canal, in 98% of women the EAS is shorter interiorly compared with the posterior area. [8,9] Where the EAS fibres slope anteriorly, it gives an apparent anterior sphincter defect, which creates the liability of obstetric injury in the internal anal sphincter (IAS). 
In the distal anal canal, the IAS is thin; therefore, we measured the PBT, anterior anal sphincter defect and anal sphincter defect angle at the level of the mid-anal canal, which can be clearly delineated by the presence of the most prominent hypoechoic ring of the IAS. 
The aim of this study was to determine the role of PBT in the assessment of a group of multiparous patients who had undergone deliveries more than once, and had developed obstetric faecal incontinence.
Patients and methods
120 multiparous patients underwent EAUS for evaluation of PBT and faecal incontinence between January and December 2016, in a prospective clinical study at the colorectal subspecialty department in Shahid Faghihi Hospital, Shiraz, Iran.
Only 80 patients met the inclusion criteria (multiparous patients who agreed to take part in the study procedure and filled out the consent form), and were categorised into two groups. Group 1 comprised 44 patients who had already presented with faecal incontinence due to obstetrical injuries. Group 2 included 36 subjects who were asymptomatic. Post-hoc calculation by power analysis on the derived results showed 80% power for this sample size. The exclusion criteria were patients who were nulliparous or primiparous, and those who had had radiation injury, low colorectal anastomosis, diabetes mellitus, ulcerative colitis, Crohn's disease or neurological disease. Also excluded were those with chronic constipation or diarrhoea, hypo- or hyperthyroidism, hypo- or hyperparathyroidism and those having undergone perineal or prolapse surgery such as sphincteroplasty, sphincterotomy, perineoplasty or pelvic floor repair.
Age, obstetric history and degree of incontinence were recorded for each patient. The degree of faecal incontinence was measured using Wexner's incontinence scale (0-20). The patients were placed in the left lateral decubitus position. As a standard protocol, we started our examination with anal manometry, followed by EAUS. In this study, perineal body thickness, anal sphincter maximum squeezing pressure, mean resting pressure (MRP), external anal sphincter defect (EASD) and sphincter angle were evaluated.
For more detailed evaluation, the patients were subdivided into three groups according to the perineal body thickness: PBT <10 mm, 10-12 mm and >12 mm.
This was performed by a special sphinctometer system (Promedico, Germany, Version 1.51); the device allows quick and precise measurements of the anal sphincter muscle tone during relaxation and squeezing condition. The measured value can be read off the device after inserting a specific sensor in the anal canal. The sphinctometer's effective range is between 0 and 300 mmHg.
A two-dimensional EAUS machine using a Bruel and Kajaer medical ultrasound scanner (Herlev, Denmark) Merline Type 1101, with a 2050 model of 360-degree rotating endoprobe transducer. The transducer frequency range was 3.75-20 MHz. EAUS was performed by an endoprobe covered with the middle finger of a disposable latex surgical glove, with ultrasound gel applied to both surfaces and introduced into the rectum. The ultrasound picture was controlled by two buttons in the proximal part of the endoprobe handle in the upward and downward direction through the anal canal, in a panoramic view.
Sonographically, the anal canal is divided into three levels: the upper level, determined by the U-shaped puborectalis muscle sling that opens anteriorly; the middle level, where the IAS is at its greatest thickness; and the lower level, which is determined by maximum thickness of the subcutaneous EAS and thinnest IAS.
A gloved lubricated finger was inserted into the vagina, touching the posterior wall with gentle pressure, while the endoprobe was in the anal canal; during the process, the EASD, external anal sphincter defect angle (EASDA) and PBT were evaluated at the mid-anal canal level [5,10] on a frozen ultrasound picture. No bowel preparation was done before the procedure.
The EASD is a homogenous hypoechoic or mixed echogenicity defect within the external muscle ring.  Scarring is represented by a change in echogenicity, which was not described as a defect. The EASDA is described as the maximum angle of separation of the edge of the defect, and measured from the centre of the probe. [5,10] The PBT is defined as the distance between the sonographic reflection of the gloved index finger and the inner border of the IAS at the midanal canal level. [3,5]
Endoanal manometry was performed by the colorectal nurse specialist, and EAUS was performed by a single operator who was a colorectal surgeon, and the results were evaluated by two experienced endoanal sonographic colorectal surgeons. The study was approved by the ethics committee of Shiraz University of Medical Sciences (ref. no. 10834).
All statistical analyses were performed using Statistical Package for Social Sciences software version 15 (SPSS, USA). Quantitative data were analysed by f-test or analysis of variance. The correlation between groups for the categorised variables was analysed by [chi square] tests and the Pearson or Spearman correlation test. P<0.05 was considered statistically significant.
Eighty multiparous females with a mean age of 46.9 years (range 26-77 years) who had had two or more previous deliveries underwent EAUS and PBT measurement.
PBT and symptoms of faecal incontinence
EAUS showed a PBT of 10 mm or less for 48 (60%) out of 80 patients. Twenty-four (30%) had a PBT of 10-12 mm, and 8 (10%) had a PBT >12 mm. The mean Wexner score was 8.6 (0.7) (range 2-20 in incontinent patients). The mean duration of incontinence was 50.3 (12.1) months. The means of resting pressure and squeezing pressure were significantly different between continent and incontinent patients (Table 1). We also observed a significant correlation (p=0.007) between PBT and age. The duration of incontinence was also significantly correlated with PBT (Table 2). The negative correlation coefficient r showed that with the increase in the PBT, those parameters decreased, while positive r showed that the direct relationship means that with the increase in the PBT, the parameters increased.
Twenty-two patients in the group with PBT <10 mm were incontinent with a sphincter defect, and 8 of the 22 had a Wexner score of 10-20; 6 incontinent patients with PBT 10-12 mm had a sphincter defect, and 3 of these had a Wexner score of 10-20. Three incontinent patients with PBT >12mm had EASD, and 2 of the 3 had a Wexner score of 10-20. There were no significant differences between the three groups of PBT in Wexner score or EASD, and the number of episiotomies in incontinent patients.
PBT and EASDA
A total of 45 patients had EASD, while 35 did not, and PBT was significantly different between them (p=0.015). Furthermore, MRP was significantly different (p=0.008), but squeezing pressure was not significant (p=0.138).
Sphincter defects were seen in EAUS in 56.25% of the patients in the range of 40 - 195[degrees] (mean; 100.8[degrees]), and the patients were separated according to defect into three groups, as follows: 29 out of 48 (60.42%) patients with PBT <10 mm, 12 of 24 (50%) patients with PBT 10 - 12 mm, and 4 of 8 (50%) patients with PBT >12mm. Squeezing pressure was significantly different among the three groups (p=0.004).
There was a history of normal vaginal delivery for 71 (89%) patients (mean 3, range 2-15).
It was found that 90.9% of 45 women with a defective anal sphincter were incontinent.
Fourteen (31%) patients with an angle defect were not clinically incontinent, and there was no significant difference between continent and incontinent patients (p=0.14).
Our study evaluated faecal incontinence in multiparous women, PBT and the EASD. The study demonstrated that in a group of incontinent women, a sonographically 'thin' perineal body (PBT <10 mm) was associated with anal sphincter defects in 73.3% of the cases. This result is in the same line with previously published findings, exclusively obstetric ones. 
Incontinence is a multifactorial condition, including changes in stool consistency and volume, decreased anorectal sensation and angle, lack of a compliant reservoir, disruption of the anal sphincter integrity, pudendal nerve neuropathy and mental function. It is defined by two mechanisms--direct injury (more often during the first delivery; commonly 35% of women develop occult sphincter injury, and sustain their symptoms of urgency and transient incontinence), and traction neuropathy of the pudendal nerves (42% with subsequent vaginal deliveries who have EASD may develop impaired continence). [11-14] It is now established that occult or unrecognised mechanical disruption to the anal sphincter is a major aetiological factor. 
Zetterstrom et al.  measured the PBT (mean 12.2; SE 3.5 mm) in asymptomatic primigravida subjects without EAUS evidence of sphincter injury in their first trimester, and defined this as normal PBT, while PBT of [less than or equal to] 10 mm is considered abnormal, and was found in 93% (39 of 42) of incontinent women with an obstetric trauma to the anal sphincter.
In our results, the PBT was significantly different between continent and incontinent patients. There were significant relationships between PBT and MRP and squeezing pressure, which was not found in a study by Titi et al.  The IAS is responsible for 50%-85% of the resting tone,  and even in the presence of an intact EAS, this relationship may explain the vulnerability of the IAS to obstetric damage.
EASD was shown in 56% of patients during EAUS. Also, we found that there was a significant negative correlation between PBT and EASD, which means that thin perineal body is associated with a large angle of sphincter defect. Thinning of the perineal body is a well-known clinical finding among incontinent women with sphincter defect.
PBT was divided into three groups. PBT <10 mm was found in 60% of multiparous patients, and 30 patients (62.5%) were incontinent in this group. Although this percentage is lower than that found by other studies, [2,5,15] these studies showed that all patients were suffering symptoms of incontinence, while in our current study, 45% of the patients were asymptomatic and multiparous.
It should be noted that the other studies [2,5,15] did not use exclusion criteria such as those in our study, where perineal surgical repair, rectal surgery for prolapse and rectocele, and nulliparous women, were excluded, so the real significance of the PBT effect is yet to be found.
PBT scores that ranged between 10 and 12 mm were found in 30% of patients, 8 (18%) of whom were incontinent, and those with PBT >12 mm comprised 10%, 6 (13.6%) of whom were incontinent. Therefore, the highest level of incontinence with EASD was found in the group with PBT <10 mm, and the lowest in the PBT >12 mm group; this is similar to the findings of other studies. [2,5,15]
The reason for this is probably the fact that the mean number of vaginal deliveries in the Zetterstrom et al.l5] study was 2.3 (range 1 -6), and in Titi et al.  it was 2 (range 1-3), as against the mean of 3 (range 2-15) in our study; in addition, some patients had undergone one or more prior episiotomies during delivery, or had a history of abortion, previous fistula surgery, anal abscess or haemorrhoidectomy one or more times, factors that greatly affect EASD and PBT.
The age of the patients was another factor that was considered, and a significant correlation with PBT was seen. Primary degeneration of the IAS could be the cause of thinning in the sphincter muscles of elderly patients.  In one study,  however, there was no evidence found the sphincter defect in older women with thinner perineal body. In some studies, there was no significant relationship between PBT and Wexner score, i.e. degree of faecal incontinence. [2,5,18] The reasons for this are not clear, as mechanisms that maintain continence are multifactorial.
Faecal incontinence is a common and usually unrecognised medical problem in females, especially after traumatic vaginal delivery. [13,14] In our study, 56% of patients had a sphincter defect demonstrable by EAUS. There was no significant correlation between PBT and Wexner incontinence score. Twenty-two patients in the group with reduced PBT were incontinent with a sphincter defect, and 8 of these had a Wexner score of 10-20. Six incontinent patients with PBT 10-12 mm had a sphincter defect, and 3 of these had a Wexner score of 10-20. Therefore, about two-thirds of women with incontinence had a reduced PBT. Finally, the routine addition of PBT to EAUS during the evaluation of faecal incontinence can be worthwhile.
Acknowledgements. We thank Fahimeh Hajhosseini and Shahla Fereydooni for their assistance with the colorectal procedures.
Author contributions. AMAHA: study design, data gathering, manuscript preparation, final approval. MAA: data gathering, data analysis, final approval. SVH: study design, manuscript preparation, revision, final approval. HK: study design, data analysis, manuscript preparation, revision, final approval. LM: data gathering, data analysis, final approval. SP: data analysis, manuscript preparation, revision, final approval.
Conflicts of interest. None.
Accepted 28 October 2018.
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A M A H Alhurry, (1) MD; M A Akool, (2) MD; S V Hosseini, (3) MD; H Khazraei, (3) PhD; L Moosavi, (3) MS; S Pourahmad, (4) PhD
(1) Department of General Surgery, Al Hussein Teaching Hospital, Kerbala, Iraq
(2) Department of Surgery, Medical College, Jabir Ibn Hayyan Medical University, Najaf, Iraq
(3) Colorectal Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
(4) Department of Biostatistics, Shiraz University of Medical Sciences, Shiraz, Iran
Corresponding author: H Khazraei (firstname.lastname@example.org)
Table 1. Data from patients in clinical continent and incontinent groups shown by mean (SE) Patient characteristic Incontinent (n=44) Age (years) 47.9 (1.8) Squeezing pressure (mmHg) 65.1 (5.1) Mean resting pressure (mmHg) 18.4 (2.0) PBT (mm) 8.78 (0.4) Digital angle degree of anal 104.9 (5.78) sphincter defect ([degrees]) Patient characteristic Continent (n=36) p-value Age (years) 45.7 (1.8) 0.395 Squeezing pressure (mmHg) 91.7 (5.7) 0.001 Mean resting pressure (mmHg) 30.6 (1.9) <0.001 PBT (mm) 9.91 (0.2) 0.035 Digital angle degree of anal 91.64 (5.41) 0.14 sphincter defect ([degrees]) SE = standard error; PBT = perineal body thickness. Table 2. Correlation between PBT measurements and other parameters Parameter PBT (r) P-value MRP 0.336 * 0.001 Squeezing pressure 0.45 * <0.001 Wexner score -0.219 ([dagger]) 0.051 Duration of disorder -0.293 ([dagger]) 0.008 Age 0.297 * 0.009 EASDA -0.30 ([dagger]) 0.045 PBT = perineal body thickness; MRP = mean resting pressure. * Pearson correlation coefficient. ([dagger]) Spearman correlation coefficient. Table 3. Possible aetiological factors for patients with anal sphincter defects, by PBT Factor (n) <10 mm 10--12 mm >12 mm p-value Incontinent 30 8 6 0.031 Episiotomy 30 12 8 0.165 Sphincter defect 29 12 4 0.655 PBT = perineal body thickness.
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|Author:||Alhurry, A.M.A.H.; Akool, M.A.; Hosseini, S.V.; Khazraei, H.; Moosavi, L.; Pourahmad, S.|
|Publication:||South African Journal of Obstetrics and Gynaecology|
|Date:||Sep 1, 2018|
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