Purpose: Successful fistula surgery depends on accurate preoperative evaluation. It has been reported that endoanal MRI is superior to endoanal sonography in visualisation and classification of perianal fistulas. There are however no studies comparing hydrogen peroxide -enhanced 3D endoanal ultrasonography (3D HPUS) with endoanal MRI (eMRI). The purpose of this study was to compare 3D HPUS with eMRI in the evaluation of surgically proven perianal fistula disease.
Methods and Materials: Between April 2000 and April 2002, 39 patients with clinical symptoms of cryptoglandular fistula disease were referred to the colorectal surgery department of our institution. All patients were invited to undergo 3D HPUS and eMRI before surgery. Selection of patients was based on visible external opening of fistulas to make the introduction of hydrogen peroxide possible. 15 patients were excluded because no external opening was visible (n =11), patients refused either or both imaging techniques (n= 4), no surgical data was available (n=3). The remaining 21 patients ( 18 male, aged 26-71) were included in the study. The eMRI was interpreted by 2 radiologists, the 3D HPUS was performed and interpreted by 2 gastroenterologists and surgery was performed by 1 colorectal surgeon. The observers were blinded for each other's findings. The following characteristics were recorded on a standardized case report form: fistula classification according to Park's, secondary circumferential fistula tracts, secondary linear fistula tracts and location of the internal opening.
Results: Agreement for the primary fistula tract was 81% for 3D HPUS and surgery, 90% for eMRI and surgery as well as for 3D HPUS and eMRI. For secondary fistulatracts agreement for cimcumferential extensions was 67 % for 3D HPUS and surgery, 57 % for eMRI and surgery, and 71% for 3D HPUS and eMRI. For secondary linear tracts agreement was 76 % for 3D HPUS and surgery, 81% for eMRI and surgery and 71 % for 3D HPUS and eMRI . Agreement for the location of the internal opening was 86 % for 3D HPUS and surgery as well as for eMRI and surgery and 90 % for 3D HPUS and eMRI.
Conclusion: For evaluating perianal fistulas 3D hydrogen peroxide enhanced ultrasound, endoanal MRI and surgery have good agreement especially for the classification of the primary fistulatract and the identification of the internal opening. Therefore both imaging techniques can be reliably applied for the preoperative evaluation of perianal fistula disease when an external opening of fistula is seen on physical examination.
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