A 34-year-old man has recurrent perianal discharge. Examination under anaesthesia reveals a fistula whose external opening lies in the posterior half of the anus at the 5 o'clock position. According to Goodsall's rule, where will the internal opening be found?
- A In the posterior midline at 6 o'clock ✓
- B Directly radial to the external opening at 5 o'clock
- C In the anterior midline at 12 o'clock
- D At the contralateral 11 o'clock position
Correct answer: A. In the posterior midline at 6 o'clock
Explanation
Goodsall's rule states that an external opening posterior to the transverse anal line tracks along a curved path to open in the posterior midline, reflecting the horseshoe spread of infection in the postanal space. Only external openings in the anterior half track radially straight to the nearest crypt. This rule guides the surgeon to the internal opening so that the tract is not missed and recurrence avoided.
Reference: Bailey and Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.