Goodsall's Rule states that
Fistulas can be described as anterior or posterior relating to a line drawn in the coronal plane across the anus, the so-called transverse anal line. Anterior fistulas will have a direct track into the anal canal. Posterior fistulas will have a curved track with their internal opening lying in the posterior midline of the anal canal. An exception to the rule is anterior fistulas lying more than 3 cm. from the anus, which may open in the anterior midline of the anal canal.
Successful treatment of an anal fistula requires correct identification of the internal opening and accurate delineation of the course of the fistula in relation to the anal sphincters.
Goodsall’s rule is of limited use in predicting the site of the internal opening of a fistula. The closer the external opening is to the anal verge, the more likely a fistula conforms to the rule. The further a fistula is away from the anal verge, the more likely it follows a horseshoe course and less likely to conform to Goodsall’s rule.
The predictive accuracy of Goodsall’s rule was found to be 84.6% in the case of a fistula with an anterior external opening. While in the case of a fistula with a posterior external opening this found to be 69.1%. Overall predictive accuracy of Goodsall’s rule is 77%.
Satyendra Dhar MD,
