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abstract

120 - DOES THE 7TH SLICE MATTER?

120

DOES THE 7TH SLICEMATTER?

N. SUBRAMANIAM, H. DIETZ;
Obstetrics and Gynaecology, Sydney Med. Sch. Nepean, Univ. ofSydney, Penrith, Australia.

Introduction: The classicaldescription of the external anal sphincter (EAS) includessubcutaneous, superficial and deep parts1. Although theEAS is now considered to be a single functional and anatomicalentity, some authors feel that an intact distal sphincter is ofdecisive importance for continence2. On 4D trans-perinealultrasound (TPUS), the caudal slice at the level of the subcutaneousEAS is currently omitted from the diagnostic algorithm.
Objective:We aimed to determine whether inclusion of the subcutaneous EAS,i.e., the '7th slice' on trans-perineal sphincter imaging,improves prediction of anal incontinence (AI).
Methods:This was a retrospective study involving women attending a tertiaryurogynecological unit in 2015. All underwent a standardized interviewincluding St Mark’s incontinence score (SMIS), clinical examinationand 4D TPUS. Volume datasets were obtained on pelvic floor musclecontraction as described previously3. Offline analysis ofarchived sphincter images was performed at a later date by the firstauthor, using proprietary software, blinded against all clinicaldata. Slices 1 to 7 were assessed for EAS defects and rated positiveif the defect angle was at least 30o (Figure 1). Thestrength of association between AI symptoms, bother score and SMISand EAS trauma in slice 7 was tested using non-parametric analysis.ROC statistics were used to compare the predictive value of modelscontaining 6 or 7 slices.


Figure 1: 3D TPUS of analsphincter showing EAS defects in all 7 slices.
Results: 463women were seen during the study period. Ultrasound volumes weremissing in 18 patients and of poor quality in 2, leaving 443 foranalysis. Mean age was 56.5 (20-88) years with mean BMI of 29.3(15.7-64.4) kg/m2. Median parity was 2 (0-8), 88 % (n=390) werevaginally parous and 25% (n=115) had a history of forceps delivery.AI was reported in 56 (13%) patients, with a median St Mark’s scoreof 11 (IQR 2-22). While there was a highly significant associationbetween all measures of AI and significant EAS trauma in slice 7(Table 1), addition of the 7th slice to the existing 6-slice modeldid not improve the predictive value for AI. As most women withsignificant EAS trauma remained asymptomatic of AI, the correspondingAUC values were low but similar for both (Figure 2).

Table1: Odds ratio of significant outcome for diagnosing significantEAS trauma of the 7th slice

Measuresof AI

OR(CI 95%) (p value)

Fi(yes/no)

4.01(1.85-8.91)(p<0.001)

FiBother (0-10)

1.17(1.05-1.30) (p=0.006)

SMIS(0-24)

1.11(1.05-1.18) (p<0.001)



Figure 2: ROC for theassociation between AI and all 6 slices and all 7 slices for EAStrauma. A) 6 slices (blue), AUC 0.62 (CI 0.54-0.71, p=0.003); B) 7slices (green), AUC 0.62 (CI 0.54-0.71, p=0.003); n=443.
Conclusions: Inclusion of the subcutaneous slice ofthe EAS on TPUS does not seem to improve the predictive value of thismethod for AI. Hence, the validated 4/6 slices criterion forsignificant EAS trauma on tomographic ultrasound can remainunchanged.
References:
1. Brit. J. Surg. 1972;9:717-723
2. Dis Colon Rectum 2000; 45:188-193
3.Ultrasound Obstet Gynecol 2015; 46:363-366