Step 1: Spot the diagnosis:
Pain during and after defecation, bright blood streaks, a posterior midline tear, a sentinel tag and visible internal sphincter fibres together mean a chronic anal fissure.
The fibres seen at the base of the tear are the white transverse fibres of the internal anal sphincter.
Step 2: Think about the mechanism:
The internal sphincter goes into spasm because of pain. This raises the resting anal pressure.
The posterior midline has relatively poor blood supply, and high pressure worsens it. The tear becomes ischaemic and does not heal.
So the fix must lower the resting pressure of the internal sphincter. Medical ways are nitroglycerin, diltiazem and botulinum toxin. The surgical way is cutting part of the muscle.
Step 3: Choose the operation:
The operation that reduces internal sphincter pressure in a controlled and measured way is lateral internal sphincterotomy.
It is done in the left or right lateral position, away from the fissure, so that healing at the fissure site is not disturbed. Only the internal sphincter is cut.
Step 4: Rule out the others:
Uncontrolled manual dilatation (Lord's procedure) gives unpredictable damage to both sphincters and a risk of incontinence. It is outdated.
Advancement flap is kept for low-tone fissures, stenosis or failed sphincterotomy. It is not the first surgery here.
Removal of the sentinel tag alone leaves the high sphincter tone untreated, so the fissure returns.
Lateral internal sphincterotomy is therefore the right choice.
Step 5: Points about the procedure:
The cut divides the lower third to half of the internal sphincter, up to the dentate line. The external sphincter is never touched.
Healing rate is above 90%. A small risk of minor gas or soiling incontinence remains, which is why the patient should have normal continence before surgery, and he does.
The result is a drop in resting pressure, better blood flow to the posterior midline and healing of the tear.
Final Answer:
Lateral internal sphincterotomy is the definitive surgery for a chronic fissure with raised sphincter tone after failed medical care. The answer is option (D).