According to Goodsall's rule, what happens if the external opening of an anal fistula is located below the transverse anal line?

Goodsall's rule is a guideline that helps to predict the internal opening of an anal fistula based on the location of its external opening. When the external opening of an anal fistula is located below the transverse anal line, this indicates that the fistula will typically have a midline posterior course within the anal canal. This is due to the anatomical features and the typical behavior of fistula formation in relation to the anal canal and its surrounding structures.

If the external opening is below the transverse anal line, the internal opening will generally follow a posterior trajectory, centrally located around the anal canal. This rule is significant for planning surgical interventions, as understanding the anatomy helps in achieving complete and effective fistula treatment.

Other options, while related to the anatomy and understanding of anal fistulas, do not accurately reflect Goodsall's rule for openings below the transverse anal line. For instance, an opening into the anal canal in a midline anterior position would not occur under these circumstances, as the posterior trajectory is the defining characteristic when the external opening is low.