An anal fissure is a tear in the squamous epithelial mucosa of the anal canal. They occur between the anocutaneous junction and the dentate line. The generally accepted etiology of anal fissures is the mechanical tearing from the passage of a hard stool, however the pathophysiology is likely to be multifactorial and may involve anodermal ischemia, infection, chronic constipation, and/or hypertonicity of the smooth muscle of the internal anal sphincter and its elevated resting pressure.
Fissures most often occur in the posterior midline, and the reasons for this are both anatomic and functional in nature. The posterior commissure of the anoderm is less well perfused than other regions. Furthermore, before the branches of the inferior artery reach the anoderm, they course perpendicularly through the septa of the internal anal sphincter. Thus, flow through these arteries is threatened by elevated intramuscular pressure of the internal anal sphincter, and in fact, studies have demonstrated that patients with anal fissures tend to have elevated anal canal pressures.
Additionally, women occasionally have anterior fissures, and lateral fissures typically suggest an unusual diagnosis (Crohn's disease, STD, malignancy).
A careful history and physical exam will usually suggest the diagnosis. Patients often complain of a history of constipation or excessive diarrhea. Pain is common, particularly with defecation and may be disproportionate to the size of the lesion. If bleeding is present, it is usually bright red, and in fact, is the most common cause of bright red blood per rectum (BRBPR) at any age.
The diagnosis is made by inspecting the anal region. Gentle retraction of the buttocks will reveal the tear. Having the patient bear down will aid in seeing a fissure if it is present. In cases where a fissure cannot by seen, a digital exam should be done to rule out other pathology. Likewise, if pain limits the diagnosis, an examination under anesthesia would be appropriate.
If the fissure is chronic, a small, external, skin tag (sentinel tag) may be identified at the base of the laceration. Additionally, if the fissure exposes internal sphincter fibers and there are hypertrophied anal papilla at the level of the dentate line, then this triad of features is generally considered pathognomonic for chronic fissures.
Acute anal fissures rarely require surgery. Conservative treatment of a dietary modification, stool softeners, and Sitz baths usually suffice. Symptoms from an acute fissure usually resolve over 10-14 days with conservative treatment, however it may take 6-8 weeks for a fissure to actually heal.
If after 6-8 weeks, the tear has not healed, the fissure is considered chronic and more active measures can be employed.
Chemical sphincterotomy employing nitro-glycerin ointment (NTG) can be attempted, where the ointment is applied topically to help heal the wound, however, headache and diarrhea are common complications. Topical diltiazem can also be used, with less reported side effects. Lastly, botulinum toxin can be injected to reduce internal sphincter tone and promote healing, however this approach is more invasive and costly than the topical treatments.
As mentioned above, surgery is rarely needed for an acute fissure, as conservative management usually suffices. If a fissure persists despite medical management, then a lateral, internal sphincterotomy can be performed. The purpose of the procedure is to cut the hypertrophied internal sphincter, thereby releasing tension, and allowing the fissure to heal.