Goodsall's rule
Last reviewed 01/2018
Goodsall's rule is applied to the examination of anal fistula. It states that
- if the external opening of a fistula lies posterior to a line drawn from 9 o’clock to 3 o’clock then it tracks around the anus laterally and opens into the midline posteriorly.
- if the external opening lies anterior to this line, then it opens directly into the anal canal
It should be noted that application of this rule is often unreliable in anterior fistulas and those with underlying disease (1).
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