The Dentate line (Pectinate line) differentiates external and internal hemorrhoids. External hemorrhoids are located below the dentate line and drain via the inferior rectal veins into the pudendal vessels and then into the internal iliac vein. These vessels are covered by anoderm that is comprised of modified squamous epithelium. As a result, these tissues contain pain fibers and affect how patients present and are treated. Internal hemorrhoids lie above the dentate line and are covered by columnar cells that have visceral innervations.
Dentate Line and Hemorrhoids
Hemorrhoids are generally classified on the basis of their location and degree of prolapse. Internal hemorrhoids originate from the inferior hemorrhoidal venous plexus above the dentate line and are covered by mucosa, while external hemorrhoids are dilated venules of this plexus located below the dentate line and are covered with squamous epithelium. Mixed (interno-external) hemorrhoids arise both above and below the dentate line.
Symptoms from hemorrhoids are similar to other diseases and the differential diagnosis should include anal fissures, rectal prolapse, abscesses and fistulas, inflammatory bowel disease, and neoplasia. The clinical history provides clues to the etiology. Pain generally indicates a process that is distal to the dentate such as a fissure or thrombosed hemorrhoid. Bleeding is nonspecific and can result from a fissure, polyps, or cancer, inflammatory bowel disease (IBD), internal hemorrhoids, or an ulcerated thrombosis.
Hemorrhoid ligations are accomplished through an anoscope by grasping the hemorrhoid and redundant mucosa with a ligator above the dentate line. If pain is encountered, the ligation should not be performed at that site and regrasping more proximally should be performed to ensure it is insensate. The band should then be applied to the base of the tissue away from the dentate line. Over the next week the tissue distal to the ligation becomes ischemic and sloughs off. The result is tissue reduction and a scar that fixes the remaining tissue in place.
How are hemorrhoids classified?
External hemorrhoids originate distal to the dentate line of the anus and are covered by squamous epithelium. External hemorrhoids may thrombose or become filled with clotted blood. Typically these are painful involving the anoderm.
Internal hemorrhoids arise above (proximal to) the dentate line and are covered with transitional and columnar epithelium. First-degree hemorrhoids swell and bleed. Second-degree hemorrhoids prolapse and spontaneously reduce. Third-degree hemorrhoids prolapse and can be manually reduced, whereas fourth-degree hemorrhoids are irreducible. Typically these are not painful above the anoderm.
Anal crypts are pockets between grooves formed by rectal columns at their distal point ending at the dentate line. Anal cryptitis, as separate from fistula, is debatable and rare.
Symptom: pain worsened by bowel movement.
Signs: localized tenderness and redness at dentate line; rectal spasm. Rule out rectal fissure. Chronic cases suggest bacterial infection of gonorrhea.