A 32-year-old man has a recurrent perianal discharge through an external opening located in the posterior half of the perineum at the 7 o'clock position. According to Goodsall's rule, where will the internal opening most likely be found?
- A At the posterior midline at the 6 o'clock position ✓
- B Radially opposite at the 1 o'clock position on the anal canal
- C At the anterior midline at the 12 o'clock position
- D Directly radial to the external opening at 7 o'clock
Correct answer: A. At the posterior midline at the 6 o'clock position
Explanation
Goodsall's rule states that an external opening behind the transverse anal line drains by a curved tract into the posterior midline, while an opening in front of the line opens radially and directly into the anal canal. B 7 o'clock opening lies in the posterior half, so the internal opening is expected at the posterior midline. The exception is an anterior external opening more than 3 cm from the anal verge, which may still track to the posterior midline.
Reference: Bailey and Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.