Anal Acoustic Reflectometry and EndoFLIPTM in the Assessment of Anal Sphincter Function in Patients with Faecal Incontinence and Rectal Prolapse

Abstract

Introduction Anal acoustic reflectometry (AAR) quantifies anal sphincter function during opening and closing of the anal canal. In assessing resistance to distension, AAR provides unique insights into sphincter function in faecal incontinence (FI). Recently, using AAR we have explored the relationship between internal anal sphincter dysfunction in rectal intussusception (RI) and external rectal prolapse (ERP). However, with a lack of commercial investment, the generalisability of any findings are limited. Therefore, research with EndoFLIP (FLIP), the only commercially available product to measure sphincter distensibility, has been conducted together with AAR. Aims & Methods This thesis includes a series of prospective studies investigating AAR and FLIP alongside established tests of anal sphincter function. The principal aims were to explore the short- and long-term outcomes of RI and ERP through two cohort studies, including the first ever in RI. Both AAR and FLIP were used in healthy volunteers and patients to establish if they were comparable, whilst investigating the reliability of FLIP. The utility of AAR and FLIP in the investigation of FI were then explored alongside high resolution anorectal manometry. Finally, AAR and FLIP were used to explore the effects of sacral nerve stimulation (SNS). Results In a longitudinal study of RI (n = 29), there were no significant changes in symptoms, or development of ERP at long-term follow-up (66 months), despite a trend towards reduction in AAR measurements beyond what would be expected with ageing alone. Following surgical repair of ERP (n = 16), anal sphincter function appeared to improve in the short-term (12 months). In a study of 9 healthy volunteers, and 55 patients, measurements of resting and squeeze function were comparable between AAR and FLIP, although differences exist between them explained by contrasting technologies and data analysis techniques. The repeatability of FLIP was clinically acceptable compared to manometry, however there were differences between the two available FLIP measurement protocols which now requires standardisation. In the investigation of FI in 40 patients, incremental squeeze pressure measured with FLIP demonstrated the strongest correlation with FI symptoms (rs = 0.414; p < 0.001). All three modalities (AAR, FLIP, and HRAM) demonstrated differences between the known FI subtypes (urge, passive, and mixed), however only the FLIP parameter functional sphincter area (FSA) was different in patients with sphincter defects. Following treatment with SNS for one month in 14 patients, increases in squeeze function and FSA were identified with FLIP, which decreased after cessation of SNS for one hour. Conclusions AAR, and now FLIP, continue to provide unique and clinically relevant insights into anal sphincter function in patients with RI, ERP, and FI. Further work is now required to standardise FLIP measurements and identify its role in the investigation and management of anorectal dysfunction.

Date of Award	31 Dec 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	John Mclaughlin (Supervisor), Dipesh Vasant (Supervisor) & Karen Telford (Supervisor)