A 35-year-old man has recurrent discharge from an external fistulous opening in the perianal skin at the 7 o'clock position (posterior half of the anus). According to Goodsall's rule, where will the internal opening be found?

• A Directly radial to the external opening
• B At the corresponding point on the opposite side of the anus
• C In the anterior midline
• D In the posterior midline ✓

Explanation

Goodsall's rule states that an external opening lying in the posterior half of a transverse line across the anus communicates through a curved tract with an internal opening in the posterior midline. Only external openings in the anterior half open radially and directly into the anal canal. This rule guides identification of the internal opening during fistulotomy and helps avoid missing a horseshoe extension.

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

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Written and medically reviewed by the StethoPrep medical team.