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Objective Perianal fistulizing disease is a problem in patients with Crohn’s disease (CD) because they often need repetitive surgeries. Among the various available procedures, none of them proves to be superior. In addition, the long-term outcome of fistula Seton drainage is not well described. The aims of this study were to analyze the long-term healing and recurrence rates of perianal fistulas in CD patients, stratified according to the first procedure performed. Methods Database analysis of a prospective Swiss cohort of patients with perianal CD. Results 365 patients with 576 interventions and a median follow-up of 7.5 years (0 - 12.6) were analyzed. 39.7% of patients required more than one surgery. The first surgical interventions were fistulectomies (58.4%), Seton drainage (26.9%), fistula plugs (2.2%) and combined procedures (9.9%). Fistulectomy patients required no more surgery in 67.6%, one additional surgery in 25.4% and more than one additional surgery in 7.7%. In these 3 groups of patients, after a median follow-up of 12.1 years, perianal fistula closure was achieved in 77.1%, 74.1% and 66.7%, respectively. In patients with Seton drainage as index surgery, 50.3% required no more surgery and over 75% achieved fistula closure after 10 years. 49.7% of patients with Seton required one or more surgeries. At median follow up of 7.5 years, closure rates were 64.2% and 60.5% in patients with one and more than one surgeries, respectively. There was no difference in demographics in Seton patients with closed or not closed fistulas. Non-closure patients had a higher Crohn Disease Activity Index (33 vs. 6) and more frequent anti-TNF medication (57.4% vs. 48.1%). Conclusion First line fistulectomies achieved the highest healing rates in perianal CD but 1/3 of patients require additional surgeries and 1/4 patients will remain with a fistula at 10 years. Initial seton drainage and concurrent medical therapy can achieve fistula closure in 75%. However, in 50% of patients more surgeries are performed with a seton staying in place up to 5 years and fistula closure in only 2/3 patients.

In the present paper, the turbulent mixing and structure of decaying stably stratified flows are investigated using direct numerical simulations (DNS). A key quantity for estimating turbulent diapyncal mixing in stably stratified flows is the flux Richardson number Rf (also commonly referred to as the mixing efficiency) which is a measure of the amount of turbulent kinetic energy that is irreversibly converted to background potential energy. Using simulations with varying strengths of density stratification, it is found that when the buoyancy Reynolds number R e b = ϵ / ( ν N 2 ) (where ϵ is the turbulent kinetic energy dissipation rate, ν is the kinematic viscosity, and N is the Brunt–Vaisala frequency), is less than 10, Rf becomes a property of the fluid as strong buoyancy effects inhibit turbulent mixing and hence Rf is influenced by (molecular) Prandtl number effects. On the other hand, for energetic flows at higher buoyancy Reynolds numbers (i.e. Reb > O(10)), Prandtl number effects diminish, indicating that Rf is a property of the flow. Flow visualization of enstrophy structures show the presence of elongated vortex tubes characteristic of classic isotropic turbulence for weakly stratified flows while ‘pancake-like’ structures emerge for strongly stratified flows.

Background Data of large cohort studies on the fate of perianal fistulizing Crohn’s disease (CD) is scarce. We aimed to evaluate the prevalence and natural history of perianal fistulas in adults with Crohn’s disease (CD). Methods Data from the Swiss IBD cohort study were analysed. The Swiss IBD Cohort study includes since 2006 IBD patients, follow-up questionnaires are completed once a year. Patients were recruited from university centres (80%), regional hospitals (19%), and private practices (1%). Results Among 2163 CD patients, 495 (22.9%) ever had perianal fistulas whereas 1668 (77.1%) did not. Patients with perianal fistulas were characterised by the following features when compared with patients without perianal fistulas: younger age at diagnosis (23.4 vs. 25.3 years, p = 0.001), longer disease duration at enrolment (9.6 vs. 4.9 years, p < 0.001), longer disease duration at latest follow-up (17.4 vs. 11.2 years, p < 0.001), less frequenty isolated ileal disease at diagnosis (15.8% vs. 28.6%, p < 0.001), more frequently rectal disease at enrolment (32.5% vs. 14.8%, p < 0.001) and latest follow-up (24.2% vs. 11.7%, p < 0.001), more frequently acne inversa (1.4% vs. 0.1%, p < 0.001), and more frequently intestinal resection (49.5% vs. 35.3%, p < 0.001). The prevalence of extraintestinal manifestations was not different (59.0% vs. 54.4%, p = 0.073). Compared with patients without perianal fistulas, patients with perianal fistulas were more frequently treated with topical 5-ASA (14.8% vs. 8.0%, p < 0.001), systemic steroids (78.2% vs. 70.1%, p < 0.001), azathioprine (82.6% vs. 77%, p = 0.008), methotrexate (28.3% vs. 22.2%, p = 0.005), infliximab (71.9% vs. 50.8%, p < 0.001), adalimumab (36% vs. 27.9%, p < 0.001), certolizumab pegol (18.6% vs. 11.5%, p < 0.001), and antibiotics (69.1% vs. 41.2%, p < 0.001). Regarding fistula anatomy, 321 patients (64.8%) had a low perianal fistula, 82 (16.6%) a high perianal fistula, and 227 (45.9%) a perineal fistula. The following fistula therapies were ever applied: perianal abscess drainage (45.7%), fistulectomy/fistulotomy (39.6%), seton drainage (28.7%), mucosal sliding flap (2%), fistula plug (1.4%), and fibrin glue instillation (1%). Conclusion In our national cohort roughly one-quarter of CD patients was diagnosed with perianal fistulizing disease. Compared with patients without perianal fistulas, patients with perianal fistulizing disease were characterised by several stigmata of complicated disease course such as a higher frequency of intestinal resections and higher prevalence of treatment with biologic agents.