What is Goodsall's rule?

Clinical relevance. Goodsall's rule guides the surgeon to the internal opening when laying open an anal fistula.

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Goodsall's rule

Goodsall's rule helps the surgeon predict the track of an anal fistula and locate its internal opening.

The rule

• Draw an imaginary transverse line across the anus.
• External opening anterior to the line: the track runs directly (radially) to an internal opening at the corresponding position.
• External opening posterior to the line: the track curves to open in the posterior midline.

Use and limits

• Helps locate the internal opening at surgery.
• It is a guide, not infallible - long anterior tracks and recurrent/complex fistulae may not follow it.