Fistulising Crohn’s desease BEN ROMDHANE M H Hopital Avicenne Bobigny France

Fistulas : serious complication of CD High morbidity and mortality Life time risk for developing a fistula in patients with CD: between 20% and 40% Perianal CD in 5–25% of CD, may be the presenting symptom of CD fistulas : one of episodic exacerbation frequently multiple, complex, recurrent Associated with active CD in small bowel (one-third) or colon( half) of the patients

goals that impact patient management: - defining fistula anatomy - Identifying underlying etiology Current imaging of fistulas include: barium fistulography small bowel fluoroscopic enteroclysis abdomino-pelvic CT CT and MR enterography (CTE and MRE) pelvic MRI ( for perianal fistulas)

CTE exploits the high spatial resolution and speed of multidetector CT MRI exploits the high contrast resolution CTE and MRE using large volumes of neutral oral contrast agents to generate exquisite images of the small bowel wall, lumen, and mesentery.

New imaging advantages over barium studies No superimposition of bowel loops No require filling of the fistulous tract fistulas typically involve: perienteric mesentery retroperitoneal space abdominal wall musculature Sinus tracts and abscesses can be readily characterized

Appearance of Crohn’s fistulas 81% appeared as extraenteric tracts. 86% were hyperenhancing compared to adjacent bowel loops hyperenhancement reflects inflammation in the fistulous tract most arose from actively inflamed large or small bowel 14% fistulas were isoenhancing, with half of these being perianal fistulas

Enteroenteric and enterocutaneous fistulas No air or fluid was seen in 68% fistulas Larger fistulas tracts filled with fluid 86% of enteroenteric fistulas and (25%) of enterocutaneous fistulas arose from a bowel segment with signs of active CD CT E able to detect patients with fistulas with an accuracy of 94%

Perianal fistulas usually hyperenhancing extraenteric tracts some perianal and enterovesical fistulas without hyperenhancement perhaps reflecting chronicity contain air 27% fluid 27% Some associated with perianal abscesses Rectovaginal fistula poorly demonstrated at CT MR examination preferred

Enterovesical and enterovaginal fistulas direct fistula tract observed in some cases or detected by secondary inflammatory signs: - thickened bladder or vaginal wall - small air intravesical or intramural at the site of fistula insertion in the bladder or vagina

Abscesses fluid collections with hyperenhancing rims multiple locations: interloop / mesenteric perianal / perirectal subcutaneous abdominal wall retroperitoneal 69% appeared to connect to bowel 89% of these bowel segments demonstrate CT findings of active inflammation

20% of CD demonstrate penetrating CD at CTE Clinical signs and symptoms protean and do not predict penetrating disease : CTE particularly beneficial No clinical suspicion in half cases with fistulas and abscess prior to CTE In those patients CRP normal in 35% of cases 61% underwent a change in medical therapy (initiation or dose escalation) following detection of penetrating CD on CTE 18% underwent surgical or percutaneous radiologic intervention following CTE

Treatment for fistulizing CD depends upon symptoms and occasionally the site and extent Radiologists should: - identify fistula , describe its location (by its proximal and distal connections), its extent (number of tracts) - identify and localize abscesses, enteric involvement by inflammatory - other superimposed conditions important in guiding appropriate management decisions

Complications should also be described abscess formation, small bowel obstruction location proximal to a stricture which may help predict the efficacy of medical or surgical management many enteroenteric, perianal F can be treated successfully with modern medical therapies enterovesical and enterovaginal fistulas often require surgical treatment

Refinements in the surgical approach to perianal complications have led to the concept of sphincter-saving procedures Need exact preoperative diagnosis In known or suspected PCD, diagnostic efforts focused on defining type, location and nature of perianal involvement

protocol Axial and coronal Axial proton density and T2 Coronal T1 spin-echo (SE) or fast spin echo with and without fat suppression Axial , coronal T1 gado fat sat

Although anal canal runs obliquely coronal nonangulated images adequate to diagnose because perianal complications spread commonly dorsal to the subcutaneous tissue More important to cover the subcutaneous tissue overlying the gluteus maximus muscle with coronal images than all parts of ventral abdominal wall

levator ani muscle separates supralevatoric from infralevatoric space some overlap exists between different compartments of the infralevatoric space divided into ischiorectal fossa, para-anal space, and subcutaneous space

Surgical approach depends on location of perianal abscess - intersphincteric abscess is drained into the anal canal - ischiorectal abscess requires a transcutaneous approach

Schematic representation of the four types of perianal fistulas as classified by Parks et al. Essary B . Pediatr Radiol (2007)

Surgical terminology Best communication with use of a common language between the referring physician and the radiologist Because perianal complications of CD were being diagnosed and treated long before MR imaging keeping the well-established surgical terminology (Parks’ classification )

Anatomic classification of perianal fistulas

In contrast to active disease, scar tissue hypointense on T1, proton density, and T2 With the use of fat suppression increased signal intensity may also be seen in scar tissue, most likely at the beginning of the healing process Same topographic approach to the different anatomic types of fistulas, and abscesses

High accuracy of MRI in separating active from inactive perianal complications: - scar tissue markedly hypointense( T1,pd,T2) - active CD hyperintense ( T2 , pd) gadolinium enhancement Combination of the two pulse sequences precludes mistaking hyperintense fatty tissue or bright signals of small blood vessels for collections If only fat-sat sequences used to differentiate scars from active CD,false positive might occur because scar can be slightly hyperintense

Coronal and transverse MRI show well the location of collections witch help surgeon to plan the intervention Differentiation between perianal abscess and fistula can be important in therapeutic decision Surgical drainage mandatory for symptomatic patient with perianal abscess Less aggressive treatment for isolated fistula MRI less sensitive in ano-vaginal fistula

limitation of CT identifying and classifying fistulas and differentiation between active fistulas and scar MRI accuracy in detection of perianal abscesses is almost 100% MRI prefered to CT when available (radiation dose ;young patient) Anal endosonography sensitive method in perianal CD With 10-MHz probes but necessity for general anesthesia, operator dependant

Conclusion 1 CTE detect clinically occult fistulizing C D Detection results in changes in patient management in the majority of cases Fistulas generally hyperenhancing, extraenteric tracts often without internal air or fluid abscesses, sinus tracts are often seen connecting to inflamed bowel loops

Conclusion 2 MRI reliable method for perianal CD: - detecting perianal abscesses and fistulas - classifying these complications according to the surgical terminology - guiding minimally invasive interventional procedures. Common language for radiologists and surgeons permits the greatest benefit for patients with perianal complications of CD