On examination of a patient with an anal fistula, the external opening lies at the 3 o'clock position, 2 cm from the anal verge, that is within the anterior half of the anus. According to Goodsall's rule, what is the expected course of the fistulous tract?

• A A curved tract passing into the posterior midline of the anal canal
• B A horseshoe tract encircling the anus to enter at 6 o'clock
• C A straight tract entering the anterior midline of the anal canal
• D A straight radial tract entering the anal canal at the 3 o'clock position ✓

Explanation

Goodsall's rule states that an external opening in the posterior half of the anus drains via a curved tract into the posterior midline, whereas an external opening in the anterior half less than halfway between the verge and the anal margin opens directly into the anal canal by a radial straight tract. Anterior openings beyond this distance behave like posterior ones and curve to the posterior midline. Horseshoe extension suggests deep postanal space infection.

Reference: Bailey and Love Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.