Goodsall’s rule : Mnemonic

Synonym: Goodsall-Salmon’s law

In anal fistula, goodsall’s rule predicts the type of track and location of internal opening.

An anterior external opening is more likely to have a straight track while a psoteriorly placed external opening is more likely to have a curved track.

Mnemonic: Think of a dog with a straight nose anteriorly and a curved tail posteriorly.

goodsall rule

However, exception exists. With the patient lying supine, an imaginary transverse, or “trans-anal” line is drawn through the ischial tuberosities. The exception to Goodsall’s rule occurs when the external opening lies anterior to the line but >3 cm from the anal verge. In this case, the tract tends to follow the rule for posterior external openings with an indirect,curved path that ends at the posterior midline (similar to posterior fistula).


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  1. Why is this 3 cm necessary for anal fistula classification and why anteriorly placed anal fistula take curved posterior position when it is greater than 3cm of anal margin

    1. Anococcygeal raphe is a fibrous median raphe in the floor of the pelvis, which extends between the coccyx and the margin of the anus. This prevents fistula from directly opening in the midline posterior anal orifice. Cutaneous openings which lie anterior, or ventral, to transverse anal line typically are connected to the anal canal via a radial tract. The reason for exception of long anterior fistula opening posteriorly might be because of these often being high transsphincteric and suprasphincteric fistulas, which have their internal openings and primary abscesses located posteriorly and penetrate the external anal sphincter.

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