Hemorrhoids
(PILES)
Medical Author:
Jay W. Marks, MD
Medical Editor:
Thomas P. Sokol, MD, FACS, FASCRS
What are hemorrhoids?
A precise definition of hemorrhoids does not exist, but they
can be described as masses or clumps ("cushions") of tissue within the anal
canal that contain blood vessels and the surrounding, supporting tissue made
up of muscle and elastic
fibers. The anal canal is the last four centimeters through which stool passes
as it goes from the rectum to the outside world. The anus is the opening of the
anal canal to the outside world.
Although most people think hemorrhoids are abnormal, they
are present in everyone. It is only when the hemorrhoidal cushions enlarge that
hemorrhoids can cause problems and be considered abnormal or a disease.
Prevalence of hemorrhoids
Although hemorrhoids occur in everyone, they become large and cause problems in
only 4% of the general population. Hemorrhoids that cause problems are
found equally in men and women, and their prevalence peaks between 45 and 65
years of age.
Anatomy of hemorrhoids
The arteries supplying blood to the anal canal descend into the canal from the
rectum above and form a rich network of arteries that communicate with each
other around the anal canal. Because of this rich network of arteries,
hemorrhoidal blood vessels have a ready supply of arterial blood. This explains
why bleeding from hemorrhoids is bright red (arterial blood) rather than dark
red (venous blood), and why bleeding from hemorrhoids occasionally can be severe.
The blood vessels that supply the hemorrhoidal vessels pass through the
supporting tissue of the hemorrhoidal cushions.
The anal veins drain blood away from the anal canal
and the hemorrhoids. These veins drain in two directions. The first direction
is upwards into the rectum, and the second is downwards beneath the skin surrounding the anus. The dentate line
is a line within the anal canal that denotes the transition from anal skin
(anoderm) to the lining of the rectum.
Formation of hemorrhoids
If the hemorrhoid originates at the
top (rectal side) of the anal canal, it is
referred to as an internal hemorrhoid. If it originates at the lower end of the
anal canal near the anus, it is referred to as an external hemorrhoid.
Technically, the differentiation between internal and external hemorrhoids is
made on the basis of whether the hemorrhoid originates above or below the
dentate line (internal and external, respectively).
As discussed previously, hemorrhoidal cushions in the
upper anal canal are made up of blood vessels and their supporting tissues.
There usually are three major
hemorrhoidal cushions oriented right posterior, right anterior, and left
lateral. During the formation of enlarged internal hemorrhoids, the vessels of
the anal cushions swell and the supporting tissues increase in size. The bulging
mass of tissue and blood vessels protrudes into the anal canal where it can
cause problems. Unlike with internal hemorrhoids, it is not clear how external
hemorrhoids form.
Next: What causes hemorrhoids? »
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