Hemorrhoids (cont.)
What causes hemorrhoids?
It is not known why hemorrhoids enlarge. There are several theories about the
cause, including inadequate intake of fiber, prolonged sitting on the
toilet, and chronic straining to have a bowel movement (constipation). None of
these theories has strong experimental support. Pregnancy is a clear cause of enlarged
hemorrhoids though, again, the reason is not clear. Tumors in the pelvis also
cause enlargement of hemorrhoids by pressing on veins draining upwards from the
anal canal.
One theory proposes that it is the shearing (pulling)
force of stool, particularly hard stool, passing through the anal canal that
drags the hemorrhoidal cushions downward. Another theory suggests that with age
or an aggravating condition, the supporting tissue that is responsible for anchoring
the hemorrhoids to the underlying muscle of the anal canal deteriorates. With
time, the hemorrhoidal tissue loses its mooring and slides down into the anal
canal.
One physiological fact that is known about enlarged
hemorrhoids that may be relevant to understanding why they form is that the
pressure is elevated in the anal sphincter, the muscle that surrounds the anal
canal and the hemorrhoids. The anal sphincter is the muscle that allows us to
control our bowel movements. It is not known, however, if this elevated pressure
precedes the development of
enlarged hemorrhoids or is the result of the hemorrhoids. Perhaps during bowel
movements, increased force is required to force stool through the tighter
sphincter. The increased shearing force applied to the hemorrhoids by the
passing stool may drag the hemorrhoids downward and enlarge them.
What are the symptoms of hemorrhoids?
There are two types of nerves in the anal canal, visceral nerves (above the
dentate line) and somatic nerves (below the dentate
line). The somatic (skin) nerves are like the nerves of the skin and are capable
of sensing pain. The visceral nerves are like the nerves of the intestines and
do not sense pain,
only pressure. Therefore, internal hemorrhoids, which are above the dentate
line, usually are painless.
As the anal cushion of an internal hemorrhoid continues to enlarge, it bulges into
the anal canal. It may even pull down a portion of the lining of the rectum
above, lose its normal anchoring, and protrude from the anus. This condition is
referred to as a prolapsing internal hemorrhoid. In the anal canal, the
hemorrhoid is exposed to the trauma of passing stool, particularly hard stools associated with
constipation. The trauma can cause bleeding and sometimes pain when stool
passes. The rectal lining that has been pulled down secretes mucus and moistens the anus and the
surrounding skin. Stool also can leak onto the anal skin. The presence of stool
and constant moisture can lead to anal itchiness (pruritus ani), though
itchiness is not a common symptom of hemorrhoids. The prolapsing
hemorrhoid usually returns into the anal canal or rectum on its own or can be
pushed back inside with a finger, but it prolapses again with the next bowel
movement.
Less commonly, the hemorrhoid protrudes from the anus and cannot be
pushed back inside, a condition referred to as incarceration of the hemorrhoid.
Incarcerated hemorrhoids can have their supply of blood shut off by the
squeezing pressure of the anal sphincter, and the blood vessels and cushions can
die, a condition referred to as gangrene. Gangrene requires medical treatment.
For convenience in describing the severity of internal
hemorrhoids, many physicians use a grading system:
- First-degree hemorrhoids:
Hemorrhoids that bleed but do not prolapse.
- Second-degree hemorrhoids:
Hemorrhoids that prolapse and retract on their own (with or without bleeding).
- Third-degree hemorrhoids:
Hemorrhoids that prolapse but must be pushed back in by a finger.
- Fourth-degree hemorrhoids: Hemorrhoids that prolapse and cannot be pushed back in.
Fourth-degree hemorrhoids also include hemorrhoids that are thrombosed
(containing blood clots) or that pull much of the lining of the rectum through
the anus.
In general, the symptoms of external hemorrhoids are different than the
symptoms of internal hemorrhoids.
External hemorrhoids can be felt as bulges at
the anus, but they usually cause few of the symptoms that are typical of
internal hemorrhoids. This is perhaps, because they are low in the anal canal
and have little effect on the function of the anus, particularly the anal
sphincter. External hemorrhoids can cause problems, however, when blood clots
inside them. This is referred to as thrombosis. Thrombosis of an
external hemorrhoid causes an anal lump that is very painful (because the area
is supplied by somatic nerves) and often requires medical attention. The
thrombosed hemorrhoid may heal with scarring and leave a tag of skin protruding
from the anus. Occasionally, the tag is large, which can make anal hygiene (cleaning) difficult or
irritate the anus.
Next: How are hemorrhoids diagnosed? »
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