The perianal, anal and rectal regions lend themselves to early
clinical diagnosis without the need to resort to complex investigations.
The anus, anal canal and rectum are a functional unit responsible
for the maintenance of continence of feces and flatus plus coordination
of defecation*. The basic factors responsible for continence
are the internal* sphincter, external* sphincter and the anorectal angle*. There is control by neuromuscular
The presence of a functional sphincter* also helps.
The anorectal region is a junctional* (transitional) zone. The main site of structural and functional transition is the
dentate* (pectinate) line. Epithelium, muscle, nerves,
vessels and viscera all change at this line. This has many clinical
implications such as pain and carcinoma spread.
Proper assessment* and treatment of anorectal conditions requires detailed knowledge of the anatomy of the region.
Human nature* is often a factor here also.
The anal columns (from dentate line to rectum) have a series
of (valveless) submucous veins forming a plexus (the internal rectal)
that drains into the superior rectal vein. The veins lack support
and are subject to pressure effects (hard feces, straining, pregnancy),
leading to the formation of internal* hemorrhoids. They
can be classified as first, second or third degree*.
The cutaneous part of the anal canal is drained by tributaries
of the inferior rectal vein (external anal plexus). These may dilate as external* hemorrhoids. The combination of both types of hemorrhoids is called intero-external*.
Differential diagnosis includes tumors, polyps, skin ...