Clinical Significance of 2 Deep Posterior Perianal Spaces to Complex Cryptoglandular Fistulas

Confusion exists regarding the clinical significance of the deep posterior intersphincteric space and deep postanal space to complex perianal fistulas.The purpose of this study was to assess the clinical significance of the 2 deep posterior perianal spaces and to describe in detail the courses of posterior complex cryptoglandular fistula extensions.This was a retrospective study. MRI-based characteristics of selected perianal fistulas were independently evaluated by examiners who focused on lesions in these 2 spaces and were blinded to each other's findings.This study was conducted in the colorectal surgery and radiology departments of a large university teaching hospital in China.Included in the study were patients who underwent pelvic MRI for posterior perianal fistula between October 2012 and December 2014.The occurrence rates of these 2 deep perianal space lesions in posterior cryptoglandular fistulas were determined.A total of 513 primary posterior cryptoglandular fistulas were identified in 508 patients, including 167 deep posterior intersphincteric space lesions (32.6%) and 23 deep postanal space lesions (4.5%). Of those, 173 fistulas (33.7%) were evaluated as complex. The former and latter spaces were involved in 79.2% (137/173) and 13.3% (23/173) of posterior complex fistulas. Compared with deep postanal space lesions, deep posterior intersphincteric space lesions were more common in cases with high transsphincteric or suprasphincteric fistulas (80.1% vs 15.8%), synchronous multiple transsphincteric fistulas (82.4% vs 20.6%), horseshoe-like fistulas (85.5% vs 14.5%), and supralevator fistulas (93.5% vs 16.1%). Similar incidences were also seen in cases with ischioanal-involved horseshoe-like fistulas (75.0% vs 25.0%).This study was limited by its retrospective nature.The deep posterior intersphincteric space is more likely than the deep postanal space to be involved in complex cryptoglandular fistulas and is likely to play a more important role in the management of complex cryptoglandular fistulas.