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An anal fissure, or fissure-in-ano, is one of the most common anal disorders seen by physicians. It is a linear tear or crack that extends into the anoderm from the mucocutaneous junction to the dentate line (Figure 67-1). An anal fissure usually results from the passage of hard stool that traumatizes and tears the anoderm. Frequent bowel movements with diarrhea can cause similar “cracks” that eventually result in fissures. Anal fissures are often seen in infants, but primarily are a condition of young and middle-aged adults.13 It is the most common cause of acute onset painful rectal bleeding in adults and in the first year of life.

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A fissure may be acute or chronic, occur at any age, and affect both genders equally. It is the most common cause of rectal bleeding in infants. Fissures are typically a few millimeters long and occur primarily (90%) in the posterior midline. The remaining 10% are found in the anterior area.46 There is a slight gender difference with 1% to 7% of anal fissures found anteriorly in men and up to 12% anteriorly in women.7 Atypical locations (e.g., lateral) suggest the presence of an underlying disease such as Crohn's disease, anal cancer, previous anal surgery, leukemia, syphilis, tuberculosis, and other infections.

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The anal canal begins at the level of the anorectal ring and extends distally for 4 cm to the anal verge. The internal anal sphincter and external anal sphincter muscles surround the anal canal. The internal anal sphincter muscle is a continuation of the involuntary layer of circular smooth muscle of the rectum that begins at the anorectal ring. It is contracted at rest so that the lower margin can be palpated 1 to 2 cm below the dentate line in the intersphincteric groove. The internal anal sphincter muscle supplies up to 60% of the resting tone of the anus.8 The external anal sphincter muscle is an elliptical cylinder of voluntary striated muscle tethered to the coccyx and surrounding the anal canal. Columnar epithelium lines the upper anal canal while the lower anal canal is lined by squamous epithelium. The transitional zone lies between the two different types of mucosa. The anoderm is a thin layer of stratified squamous epithelium around the anus, distal to the dentate or pectinate line, that lacks sweat glands and hair follicles. This area is richly endowed with cutaneous sensory nerve endings.

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It is hypothesized that anal fissures usually occur in the posterior midline secondary to a decreased vascular supply causing ischemia or a decreased number of external sphincter muscle fibers predisposing the posterior area to a weakness.9 Constipation or a hard bowel movement causes a tear in the anoderm that causes pain. The tear often results in a vicious cycle of injury by ...

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