The anal verge, also called the anal margin, is the surface of the ringed opening of the anus through which fecal matter is eliminated. An anus is composed of two parts: the anal canal and the anal verge. Both sections are located within the anal sphincter, which is a muscle that controls the expulsion of feces. An anal verge marks the transition point from the internal mucosa of the anal canal to the surface of the perianal skin.
Disorders of the anus often mimic the symptoms of other conditions. A change, or dysplasia, in the cells of the surface layer of the anal verge may resemble the early formation of hemorrhoids. Once an examination is performed and a biopsy of the changed tissue is taken, a condition called carcinoma in situ (CIS), or Bowen's disease, may be diagnosed. These non-invasive pre-cancerous cells usually do not spread beyond the surface layer of the verge tissue, but their presence may indicate the possibility of developing an invasive anal cancer in the future.
Anal cancer refers to a malignant growth of cells in the anal canal or verge. Cancer of the verge is sometimes called perianal skin cancer. Typically, the cancer is found to be a squamous cell carcinoma after the evaluation of biopsied tissue in a laboratory. Unlike cancer of the anal canal, the surface cancer of the verge often mimics skin cancer and is more difficult to treat.
The anal verge may also develop a malignant melanoma. Pigment-producing melanocytes are responsible for the creation of melanin, which causes the brownish color of the anus. Generally, a melanoma develops on skin that is exposed to the ultra-violet (UV) rays of the sun. Diagnosis of a malignant melanoma of the anal verge is uncommon, but if discovered in the early stages, a complete excision of the tumor can result in a full recovery.
Another cancer of the verge that is more common in skin that is exposed to excessive sunlight is a basal cell carcinoma. Treatment of this cancer involves the surgical removal of the growth. Close medical supervision is recommended to ensure any redevelopment of the cancer is diagnosed and treated quickly.
The operation for the removal of a cancer of the anal verge is called an abdominoperineal resection (APR). Typically, the rectum, anal sphincter, anal canal, and anal verge are removed, and the lower end of the intestine is attached to an opening in the abdomen called an ostomy. Most patients lose the ability to have normal bowel movements. Occasionally, the surgeon may decide to perform an intersphincteric resection (ISR) instead of an APR. This surgery allows for the excision of the cancerous growth without the subsequent loss of bowel control many people endure due to the removal of the anal sphincter and anus.