By Dr. Andrea Braini, SIUCP-ETS National Councilor
Crohn's disease (CD) is a chronic inflammatory bowel disease (IBD) that can affect any part of the digestive system, i.e. from the mouth to the anal region.
At the perianal level the clinical picture can be complex and varied; in most cases it is represented by a fistula or abscess, however there are other common manifestations such as voluminous elephant ears, fissures, stenosis up to the albeit rare cancerization. Finally, the patient with CD may be affected by non-Crohn's-related proctological pathologies (e.g. haemorrhoid prolapse) whose treatment must be as conservative as possible.
About a third of patients with Crohn's disease have a perianal localization which is more frequent the more the disease has a distal localization, affecting up to 90% of patients with involvement of the colon and rectum.
Perianal fistula is often the first manifestation of CD, particularly in the pediatric population and represents a risk factor for a more aggressive disease, significantly influencing the patient's quality of life and increasing the possibility of an intestinal diversion (ileus /colostomy) sometimes definitive.
The pathogenesis of CD fistulas, unlike cryptogenic ones, includes various factors both linked to the disease itself (defects in mucosal repair, immune disorders, inadequate intramacrophage clearance of bacteria, etc.), both to the patient (e.g. cigarette smoking) and to the therapies (corticosteroids, biologics, etc.).
From an anatomic-pathological and classification point of view, CD fistulas are complex in the majority of cases (up to 80%), with multiple external and/or internal orifices even in atypical locations, unlike cryptogenic fistulas.
Anatomically they are distinguished based on the Parks classification (Fig. 1), however it is useful to distinguish them into simple and complex, where by complex fistula (Fig. 2) we mean any fistula that cannot be treated with a simple fistulotomy/fistulectomy for reasons anatomical, for local sepsis or for the risk of incontinence (e.g. anterior fistulas in women).
Clinically they can manifest themselves with an abscess phase (Fig. 3) characterized by perianal swelling, pain and fever or in a fistulous phase (Fig. 4) with perianal secretion, blood loss and pain.
The diagnosis, as well as clinical, must be made with accurate diagnostic imaging. In particular by means of a pelvic CT scan, especially in emergencies when faced with a septic/suppurative condition; with an MRI or transanal ultrasound for a better anatomical definition of the fistula. Diagnostic imaging is able to modify the surgical approach in up to 40% of cases. Fistulography represents a test that has now been supplanted and is not recommended by current guidelines. Finally, the endoscopic study of the colorectum is of fundamental importance, as the rectal localization of the disease is one of the most significant prognostic factors on the progress of the perianal disease.
The treatment of perianal fistulas in CD is based on a multidisciplinary approach, therefore it must be carried out in reference centers where there are different dedicated professionals and an accredited team for the diagnosis and treatment of IBD. In fact, the therapeutic approach is always of an integrated medical-surgical type which allows the patient's clinical outcome and quality of life to be significantly improved.
The first therapeutic step is the control of sepsis in case of perianal suppuration. In this regard, it is advisable to drain the abscess without digging out the cavities but simply by positioning drains; furthermore, if the internal orifice is not easily identifiable, blind positioning of setons should be avoided as they could create false paths, described in up to 30-40% of emergency drained fistulas.
The distinction of the fistula into simple or complex through the diagnostic methods described has a fundamental importance, possibly including the visit under anesthesia (EUA).
The treatment of a simple fistula, particularly if symptomatic and in the absence of proctitis, remains fistulotomy or fistulectomy which leads to recovery in over 90% of patients.
The treatment of complex fistulas must always be of an integrated medical-surgical nature. In such cases the first step, especially if the fistula has collections, is a drainage with a seton (Fig. 5) and subsequent initiation of medical therapy which may initially be based on specific antibiotics (e.g. Ciprofluoxacin, Metronidazole) and subsequently with drugs biological or thiopurines.
The seton must be of the draining type (loosing seton) avoiding putting it in traction (cutting seton) due to the high risk of incontinence (up to 50% of various degrees), in addition to the pain which can affect the patients' quality of life.
Once the seton or setons have been positioned, they must be maintained at least for the induction phase of medical therapy, usually 6-8 weeks and the patient has to be monitored in particular for the development of a recurrence of sepsis which will need to be drained again with possible suspension of immunosuppressive therapy.
Once the suppurative phase has been controlled and immunosuppressant therapy has begun, there are various therapeutic options that will need to be discussed with the patient and in a multidisciplinary context.
The seton can simply be removed with a remission rate of 30-50%, continuing with biological therapy (for at least a year).
Alternatively, particularly in patients with active rectal disease and non-responders to medical therapy, the seton must be kept in place which however will not lead to healing of the fistula in most cases.
In the end, there is the surgical option for the definitive treatment of the fistula. In this regard there are many techniques available, in particular from traditional ones such as the rectal flap or fistulotomy/fistulectomy with cone-like excision to sphincter preserving ones.
The former entail risks of incontinence that reach up to 50% in some cases.
Among the sphincter preserving techniques, the most used are LIFT or intersphincteric ligation of the fistula tract, VAAFT (video-assisted treatment of the fistula), FiLaC (laser treatment of the fistula tract) as well as all the filling techniques with plugs or biological substances. Local injections of anti-TNF drugs have also been proposed which however require multiple sessions.
More recently introduced is the use of both allogeneic and autologous stem cells (Fig. 6-7) which seem to give good results especially in the short term, always in association with immunosuppressive therapy.
In symptomatic cases and non-responders to combined therapy with associated anal stenosis, a temporary diversion is indicated which, however, is only curative in the minority of patients in whom definitive proctectomy is considered.
Lastly the risk of cancerisation, although is very low, should not be underestimated, especially in patients with a long-standing perianal disease, with unexplorable anal stenosis, in the event of the appearance of mucus-blood secretions or intense proctalgia. In suspected cases, serial biopsies should be performed and, if positive, a multidisciplinary oncological therapeutic approach.
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ECCO Guidelines on Therapeutics in Crohn's Disease: Medical Treatment Journal of Crohn's and Colitis, Volume 14, Issue 1, January 2020, Pages 4–22
ECCO Guidelines on Therapeutics in Crohn’s Disease: Surgical Treatment Journal of Crohn's and Colitis, Volume 14, Issue 2, February 2020, Pages 155–168
ECCO-ESCP Consensus on Surgery for Crohn’s Disease Journal of Crohn's and Colitis, Volume 12, Issue 1, January 2018, Pages 1–16
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