Do anal fistulas in Crohn's disease behave differently and defy Goodsall's rule more frequently than fistulas that are cryptoglandular in origin?

OBJECTIVES: The complexity of anal fistulas is different in patients with and without Crohn's disease and in men and women. This may affect the localization of the internal orifice. We compared the characteristics of anal fistulas and the accuracy of Goodsall's rule in predicting the position of the internal orifice in male and female Crohn's and non-Crohn's patients.

METHODS: A total of 191 fistula tracks in 182 consecutive patients (110 men and 72 women) were analyzed prospectively. Of the patients, 63 were diagnosed with Crohn's disease. The positions of the orifices were recorded and the accuracy of Goodsall's rule determined.

RESULTS: The distribution of fistula subtypes among Crohn's and non-Crohn's patients differed significantly (p = 0.0471). Fistulas with an anterior external opening occurred more frequently in Crohn's patients (p = 0.0350) and in women (p = 0.0030). Fistulas with a posterior external orifice were observed more frequently in non-Crohn's patients (p = 0.0350) and in men (p = 0.0028). Overall, Goodsall's rule performed less well in women compared with men (p = 0.0633). The accuracy of Goodsall's rule overall was not affected by Crohn's disease. In female non-Crohn's patients, the positive predictive value of a posterior external orifice was lower than in men (p = 0.0406).

CONCLUSIONS: The distribution of fistula subtypes and the ratio of anterior and posterior external openings among Crohn's and non-Crohn's patients differ significantly. Many fistulas defy Goodsall's rule, particularly in women and when applied to fistulas with anterior external orifices. The popular rule, however, falls equally short in Crohn's and non-Crohn's fistulas.