A 34-year-old man has recurrent discharge from an external fistula opening in the posterior half of the anal circumference at the 7 o'clock position. Applying Goodsall's rule, where will the internal opening be found?

• A Directly radial to the external opening at the same clock position
• B In the posterior midline of the anal canal ✓
• C In the anterior midline of the anal canal
• D At the level of the puborectalis sling laterally

Explanation

Goodsall's rule states that an external opening in the posterior half of the anus tracks along a curved course to open in the posterior midline, reflecting flow along the intersphincteric plane. External openings in the anterior half within 3 cm of the verge open radially and directly into the anal canal. The 7 o'clock position lies in the posterior half, so the internal opening is posterior midline, not radial.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.