Skip to Main Content


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 56-1). 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. 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 occur primarily (90 percent) in the posterior midline. The remaining 10 percent are found in the anterior area. There is a slight gender difference with 1 to 7 percent of anal fissures found anteriorly in men and up to 12 percent anteriorly in women.1 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.


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 percent of the resting tone of the anus.2 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.


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.3 Constipation or a hard bowel movement causes a tear in the anoderm that causes pain. Spasm of the internal anal sphincter muscle occurs, which results in a tighter anal canal that causes more pain with subsequent bowel movements. A vicious cycle results and may lead to a chronic anal fissure.


A tight anal sphincter is another hypothesis for the etiology of a fissure. Anal manometry in patients with fissures reveals an ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessEmergency Medicine Full Site: One-Year Subscription

Connect to the full suite of AccessEmergency Medicine content and resources including advanced 8th edition chapters of Tintinalli’s, high-quality procedural videos and images, interactive board review, an integrated drug database, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessEmergency Medicine

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.