The complexity of cryptoglandular fistula-in-ano can be predicted by the distance of the external opening to the anal verge; implications for preoperative imaging?

BACKGROUND

Many surgeons believe that the distance from the external opening to the anal verge (DEOAV) predicts the complexity of a cryptoglandular fistulas-in-ano and, therefore, predicts the need for additional imaging. However, there is no evidence to support this. The primary aim of this study was to determine if DEOAV can predict the complexity of a fistula. Secondary aims were clinical outcome and identification of those patients that might not benefit from preoperative imaging.

METHODS

All patients having surgery for cryptoglandular fistula-in-ano between January 2014 and December 2016 were evaluated. Preoperative imaging was used to classify fistulas as simple or complex. The DEAOV was measured preoperatively and was divided into categories ≤ 1 cm, 1-2 cm, or > 2 cm. The relationship between the DEOAV and complexity of the fistula was investigated. Clinical outcome was recorded and a group of patients that might not benefit from preoperative imaging was identified.

RESULTS

A total of 103 patients [m:f = 65:38, median age 47 (range 19-79) years] were included. Magnetic resonance imaging identified 39 simple and 64 complex fistulas. The percentage of simple fistula was 88% in fistulas with DEAOV ≤ 1 cm, 48% in DEAOV 1-2 cm and 38% in > 2 cm. There was a significant difference between the complexity of the fistula and the distance to the anal verge (p < 0.001). The overall healing rate was 88%.

CONCLUSIONS

The complexity of perianal fistula depends on the DEAOV. We propose that preoperative imaging should be performed in fistulas with external opening > 1 cm from the anal verge.