Clinical Presentation and Diagnosis

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Prior to any discussion on neoplasms of the anal canal, it is essential to define the anal and perianal anatomy. There has been much confusion in the past regarding the anatomy of this region. Based on this, the World Health Organization described standard nomenclature for the anatomy of the anal canal, the anal verge and the anal margin. The anal canal extends from the anorectal ring to the anal verge. This is approximately 2 cm above and 2 cm below the dentate line respectively. The tissue distal to the anal verge is described as the anal margin (see Fig. 9.1).

The anal margin contains modified squamous epithelium such that it contains no skin appendages or hair follicles. The lining of the anal canal is divided into three distinct histologic types. The upper anal canal is lined by columnar or rectal type epithelium. The mid portion of the anal canal is lined by cloacogenic or transitional epithelium. Finally, the distal portion of the anal canal is lined by nonkeratinizing squamous epithelium. Electron micrographic studies have shown that squamous epithelium extends into the upper canal and that columnar epithelium can extend to below the dentate line. The distinction between the anal canal and the anal margin is an important one. Often, lesions of the anal margin can be treated with local excision without impairing sphincter function. However, lesions of the anal canal are often more invasive and require combined chemoradiation for cure.

Lymphatic drainage also differs between the anal margin and the anal canal. Above the dentate line in the upper portion of the anal canal, lymphatic drainage generally follows the superior rectal vessels into the retroperitoneum. In the mid anal canal, drainage migrates along the internal pudendal nodes to the obturator nodes. Below the dentate line, the primary lymphatic drainage is via the inguinal nodes.

Individuals with neoplastic lesions of the anus often present late. More than 50% of the individuals have had symptoms for greater than two years prior to presentation. In addition, 10-20% of individuals will have palpable inguinal metastases at the time that they are diagnosed.

Delay in diagnosis is due to a combination of patient embarrassment and fear, and missed diagnosis. Between one quarter and one third of individuals with malignancy of the anal region have been misdiagnosed with benign pathology such as hemorrhoids, fissure, fistula, eczema, or abscess. A careful history, a thorough examination, and a biopsy of any suspicious lesions should make incorrect diagnosis very unlikely.

The common presenting signs are bleeding, pain, drainage and the presence of an anal mass (Fig. 9.2). It is not surprising that anal cancers are commonly misdiag-nosed as benign lesions as the symptoms for both overlap significantly.

In any person with significant anal complaints, a complete anal and regional pelvic examination should be performed. These patients are often in pain and very

Column of Morgagni Dentate line Anal crypt Anal gland Anoderm

Transitional zone

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Column of Morgagni Dentate line Anal crypt Anal gland Anoderm

Anal margin

Fig. 9.1. Anatomy of the normal anal canal. Reprinted with permission from Gordon PH, Nivatvongs S. Principles and Practice of the Colon, Rectum and Anus, 2nd edition. St. Louis: Quality Medical Publishing, 1999.

Fig. 9.2. Perianal squamous cell cancer. Reprinted with permission from Gordon PH, Nivatvongs S. Principles and Practice of the Colon, Rectum and Anus, 2nd edition. St. Louis: Quality Medical Publishing, 1999.

anxious regarding their examination. It is imperative to put patients at ease so that a thorough exam can be performed. The patient should be examined in the left lateral decubitus position with the buttocks slightly off the examining table. The buttocks

Anal canal

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