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 85-1). 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.1-3 It is the most common cause of acute-onset painful rectal bleeding in adults and in the first year of life. Thus, some form of “trauma” results in anal sphincter spasm that causes ischemia.4,5
The anal fissure. A. Picture of an anal fissure. (Used with permission of Thieme Medical Publishers.) B. Illustration of an anal fissure.
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 (85% to 90%) in the posterior midline.5 The remaining 10% to 15% are found in the anterior area.5-8 There is a slight gender difference, with 1% to 7% of anal fissures found anteriorly in men and up to 12% anteriorly in women.9 Atypical locations (e.g., lateral) account for 1% and suggest the presence of an underlying disease such as anal cancer, Crohn’s disease, HIV, leukemia, previous anal surgery, syphilis, tuberculosis, and other infections.5,10
ANATOMY AND PATHOPHYSIOLOGY
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 approximately 2.5 to 4.0 cm long and 2 to 3 mm thick. The internal anal sphincter is not under voluntary control and is continuously contracted to prevent unplanned stooling. 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.11 The external anal sphincter muscle is an elliptical cylinder of voluntary striated muscle tethered to the coccyx and surrounding the anal canal. It merges proximally with the puborectalis and levator ani muscle. It is voluntarily controlled. Columnar epithelium lines the upper anal canal while the lower anal canal is lined by squamous epithelium. The transitional zone ...