Perianal fistula: improving diagnosis and understanding
Creators: name: Sahnan, Kapil
Publisher: name: Imperial College London
Year: 2019

description: Perianal sepsis is poorly understood both in the literature and by patients and clinicians. This limits our ability to develop a clinical trial which would help determine best practice in perianal Crohn’s disease. This thesis aims to establish the necessary background for a clinical trial in perianal Crohn’s disease, to develop an improved understanding of the natural history of perianal sepsis and explores the use of novel imaging technology to improve evaluation, understanding and communication as to the nature of perianal fistulas. (A) Epidemiology of perianal sepsis – understanding the origin Perianal abscesses and fistulas are common and represent a significant caseload within the NHS. Current understanding of the relationship between abscess and fistula comes from often old, mostly single institution studies. The same can be said about the natural history of perianal fistulising Crohn’s disease, where once again much of the epidemiological knowledge is derived from (sometimes historic) long-term population cohort studies, which are often single centre studies lacking therefore external validity and often lack the diversity of population. Using Hospital Episode Statistics (HES) and a local hospital database we have established a new estimate for the rate of fistula formation following perianal abscess, using national data over a fifteen-year period, and quantified independent predictors of fistula following abscess which include inflammatory bowel disease, female gender and the location of the anorectal abscess. (B) Assessing outcomes for perianal Crohn’s disease The lack of objective assessment tools for determining outcome following treatment of Crohn’s anal fistula means that investigators often use multiple outcome measures, that these varies between studies, and that new measures are often created. This thesis describes the creation of a core outcome set for fistulising Crohn’s disease. Core outcome sets are groups of outcome measures that have been identified through a systemic review and a Delphi process, and ratified by key stakeholders, which fundamentally includes patients. They are the outcomes which are thought most valuable and should, at the minimum, be reported in every study of that condition. We have developed an eight-domain outcome set for fistulising Crohn’s disease after surveying 187 surgeons, gastroenterologists, nurses, radiologists and patients from across the UK. (C) Creating a novel objective outcome measure There is no standardized, reproducible measure for clinicians to use to assess the effect of medical treatment of Crohn’s anal fistula. Currently the success of treatment is subjectively assessed clinically or radiologically. A local pilot study of specialist GI radiologist review of MRI scans before and after treatment with infliximab demonstrated that the radiologists were only in universal agreement on the status of a fistula around three-quarters of the time. This thesis has created the necessary background information to create a robust activity-based MRI score based on fistula volume calculation. The aim is that it will both serve as an objective adjunct to decisional algorithms, which also include clinical score and fistula anatomy, and to allow the development of predictive factors based on an objective assessment of response to treatment. (D) Improved evaluation, understanding and communication of the nature of perianal fistulas. Perianal Crohn’s fistulas are complex and recurrence/reoperation rates are high. With each surgical intervention, scar tissue forms, distorting anatomy. Whilst conventional 2D pelvic MRI is effective at defining anatomy and guiding surgery, it remains difficult for surgeons to conceptualise complex fistula. Judicious surgery relies on knowledge of exact fistula morphology in relation to the anal sphincter; without this accurate appreciation of the anatomy, injudicious, imprecise or aggressive surgery can result in incontinence and/or recurrence. This thesis describes a variety of different media of 3D reconstruction of the anorectum including the sphincter and the fistula tract(s), including the creation of 3D static images, digital animations, augmented reality platforms and 3D printed models. The 3D reconstructions have been created with the aim of improving conceptualization for trainees, patient understanding and surgical decision-making through the 3D modelling of perianal Crohn’s disease.