A 32-year-old man has a fistula-in-ano with the external opening at the 4 o'clock position on the anal verge, clearly anterior to the transverse anal line. There is no history of Crohn's disease or previous surgery. According to Goodsall's rule, where will the internal opening most likely be found?

• A In the posterior midline crypt
• B In the anterior midline crypt
• C At the crypt directly opposite on the opposite side of the circumference
• D At the crypt directly radial to the external opening, in the anterior half ✓

Explanation

Goodsall's rule states that an external opening anterior to the transverse anal line tracks by a short radial (direct) course to the crypt at the same radial position, provided the opening lies within the anterior half. Openings posterior to the transverse line, and anterior openings beyond the lateral extremes, curve into the posterior midline. Option A applies to posterior openings, and option B is wrong because even true anterior midline external openings usually drain via the posterior horseshoe tract.

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.