How is lateral internal sphincterotomy performed in the surgical treatment of an anal fissure?

Updated: Jul 24, 2020
  • Author: Lisa Susan Poritz, MD; Chief Editor: John Geibel, MD, MSc, DSc, AGAF  more...
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Lateral internal sphincterotomy is the current surgical procedure of choice for anal fissure. The procedure can be performed with the patient under general or spinal anesthesia. (Local anesthesia may even be used in the cooperative patient, though it is not always recommended). The purpose of the operation is to cut the hypertrophied internal sphincter, thereby releasing tension and allowing the fissure to heal. [12]

When first described, sphincterotomy was performed in the posterior midline at the site of the fissure, with or without a fissurectomy. [13] However, the incision for the sphincterotomy usually did not heal, for exactly the same reason that the fissure did not heal. Currently, sphincterotomies are normally performed in the lateral quadrants (right or left, depending on the comfort or handedness of the surgeon). In a properly performed lateral internal sphincterotomy, only the internal sphincter is cut; the external sphincter is not cut and must not be injured.

The sphincterotomy can be performed in either an open or a closed manner, as described below.

In a closed sphincterotomy, a No. 11 blade is inserted sideways into the intersphincteric groove laterally. It is then rotated medially and drawn out to cut the internal sphincter. Care is taken not to cut the anal mucosa, because doing so could result in a fistula. After the knife is removed, the anal mucosa overlying the sphincterotomy is palpated, and a gap in the internal sphincter can be felt through it. The sphincterotomy is extended into the anal canal for a distance equal to the length of the anal fissure.

In an open sphincterotomy, a 0.5- to 1-cm incision is made in the intersphincteric plane. The internal sphincter is then looped on a right angle and brought up into the incision. The internal sphincter is then cut under direct visualization. The two ends are allowed to fall back after being cut. A gap can then be palpated in the internal sphincter through the anal mucosa, as in the closed technique. The incision can be closed or left open to heal.

When treating a chronic anal fissure, the surgeon may elect to perform a fissurectomy in conjunction with the lateral sphincterotomy. In such cases, care must be taken not to include a piece of the internal sphincter with the excision. More simply, instead of excising the fissure along with the sphincterotomy and worrying whether it will heal, the surgeon can excise the hypertrophied papillae and the skin tag and leave the fissure to heal on its own.

Sometimes, long-standing chronic fissures do not heal, even with an adequate sphincterotomy, and an advancement flap must be performed to cover the defect in the mucosa. This can be performed either at the time of the sphincterotomy if the surgeon does not think that the fissure will heal or as a second procedure if the fissure does not heal.

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