The Evaluation and Treatment of Hemorrhoids

A Guide for the Gastroenterologist

Robert A. Ganz

Disclosures

Clin Gastroenterol Hepatol. 2013;11(6):593-603. 

In This Article

Anatomy

Why are hemorrhoids called hemorrhoids and asteroids called asteroids? Wouldn't it make more sense if it was the other way around? But if that were true, then a proctologist would be an astronaut.
Robert Schimmel (1950–2010)

The rectum extends from the terminal sigmoid colon to the anus, is lined by columnar epithelial mucosa innervated by the sympathetic and parasympathetic nervous systems, and consequently is relatively insensate. Its vascular and lymphatic supplies originate from the hypogastric system. The anal canal, which is approximately 4 cm in length, extends from the anal verge to its junction with the rectum close to the proximal aspect of the levator-sphincteric complex. Unlike the rectum, the anus is lined by anoderm, which is a modified and sensitive squamous epithelium richly innervated with somatic sensory nerves, and supplied by the inferior hemorrhoidal system.[8,24] The dentate line is the point at which the squamous anoderm meets the columnar mucosa and typically lies about 3 cm above the anal verge.[25] The dentate line is the major anatomic reference point when considering the treatment of hemorrhoids. Internal hemorrhoids are cushions of fibrovascular tissue located just proximal to the dentate line, with the external hemorrhoidal cushions lying distal to it. This terminology can seem a bit confusing, because in this context, the word external does not mean outside the anal canal, but rather distal to the dentate line; there are external hemorrhoids residing inside the anal verge (Figure 1).

Figure 1.

Illustration of normal anorectum. Courtesy of Iain Cleator, MD, Vancouver, BC, Canada.

Work by Thomson,[26] published in 1975, used both anatomic dissections along with radiologic and vascular studies to best elucidate hemorrhoidal anatomy. He noted that the submucosa in the area of the anal canal formed a discontinuous layer of thickened tissue, creating "cushions" typically found in the left lateral, right anterior, and right posterior positions, although there are frequent anatomic variations of this arrangement.[9,26] These cushions receive their blood supply primarily from the superior hemorrhoidal artery as well as branches of the middle hemorrhoidal arteries; however, there is some communication with the inferior hemorrhoidal arteries as well. The venous drainage is provided by the superior, middle, and inferior hemorrhoidal vessels, allowing for communication between the portal and systemic circulations. These vessels form direct arteriovenous communications within the cushions, and for these reasons, hemorrhoidal bleeding is arterial in nature rather than venous.[26]

The submucosal layer of these cushions contains not only the vessels mentioned above but is also rich in muscular fibers, which arise from both the internal sphincter and the conjoined longitudinal muscle. These muscular fibers (the muscularis submucosae) help to maintain adherence of these tissues to the underlying internal sphincter.[26,27] With time and aging, starting as early as the second or third decade of life, this supporting tissue can deteriorate or weaken, leading to distal displacement of the cushions and venous distention, erosion, bleeding, and thrombosis and also allowing for tissue prolapse.[3,9,26,28]

The hemorrhoidal cushions are considered to play an important role in the maintenance of rectal continence, contributing 15%–20% of the resting pressure of the anal verge. They also work to protect the sphincter mechanism during defecation, in addition to providing complete closure of the anal opening, especially while performing a Valsalva maneuver.[26,29,30]

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