Etiology and pathogenesis
The disease begins with pathology of the valve apparatus of the portal vein and its branches, specifically the rectal veins. When the valves fail to cope with their function, a local increase in hydrostatic pressure occurs. As a result of this pressure, vessel walls cannot withstand it, and the vessels begin to prolapse (bulge) into the lumen of the anal canal in the form of characteristic spherical masses.
The exact etiology of this process remains unknown. However, clinicians identify a clear set of triggering factors. These include:
- Chronic constipation.
- Repeated pregnancies.
- Inadequate physical exertion.
- Alcohol abuse.
All these conditions contribute in one way or another to blood stasis and increased pressure in the venous system.
Anatomy and Classification
Hemorrhoidal nodes do not appear out of nowhere — they form strictly in areas where cavernous veins are normally located. Anatomically and morphologically, two main types of hemorrhoids are distinguished, depending on which plexus is affected.
- Internal hemorrhoids. Develop from the internal hemorrhoidal plexus (clusters of cavernous veins) located proximal to the upper boundary of the anal canal. This is a special zone where the rectal mucosa transitions into the stratified squamous epithelium of the anal canal. Accordingly, internal nodes are always covered by rectal mucosa.
- External hemorrhoids. Form from the external hemorrhoidal plexus. It is located at the lower boundary of the anal canal, in the zone where the stratified squamous epithelium firmly adheres to the underlying tissues. Therefore, external nodes are covered by stratified squamous epithelium of the anal canal.
Morphology and Clinical Features
Despite their different locations, both venous plexuses are structured identically. Morphologically, they represent dilated veins directly fed by fine encircling arteries. This anatomical feature is of paramount clinical importance: due to constant arterial inflow, bleeding from damaged hemorrhoidal veins always exhibits pronounced features of arterial bleeding.
As the pathology progresses, the cavernous spaces gradually increase in size. They transform into full-fledged hemorrhoidal nodes that begin to prolapse in the region of the upper boundary of the anal canal.
On microscopic examination of a removed node (e.g., in external hemorrhoids) using standard staining — hematoxylin and eosin — cavernous transformation of the venous vessels is clearly visualized.
Complications
If left untreated, the condition inevitably leads to severe complications. There are two main scenarios:
- Mechanical damage. Trauma to enlarged and thinned nodes (e.g., during the passage of hard stools) leads to profuse arterial bleeding.
- Infection. The anorectal region frequently serves as a port of entry for various infections (including viral ones). Infection of the cavernous spaces triggers an inflammatory process, leading to a severe complication — hemorrhoidal thrombophlebitis.
Briefly: answers to topical questions
What do hemorrhoidal nodes look like macroscopically?
- Hemorrhoidal nodes — vessels prolapse as spherical masses into the lumen of the anal canal. Cavernous spaces increase in size, turning into hemorrhoidal nodes that prolapse in the area of the upper boundary of the anal canal. Internal hemorrhoids are characterized by nodes covered with rectal mucosa. External hemorrhoids are characterized by nodes covered with stratified squamous epithelium.
What secondary changes occur in the wall of a hemorrhoidal node during a prolonged chronic course?
- Vessel wall — thinned in areas of dilation; compensatorily thickened in other sections due to smooth muscle cell hypertrophy and sclerosis.
- Valves — sclerosed and deformed, which exacerbates venous stasis.
- Thrombosis — often combined with phlebothrombosis, thrombosis of nodes followed by canalization of thrombi.
To avoid confusing the epithelial lining of the nodes: Internal — Inside the bowel (covered with mucosa), External — External (covered with stratified squamous epithelium).
Class and exam questions
Why does bleeding from hemorrhoidal nodes have an arterial character if veins are dilated?
Fine arteries encircling the hemorrhoidal plexus drain directly into its dilated veins. Due to this constant arterial inflow, blood upon mechanical damage to the node exhibits clinical signs of arterial blood.
What is the difference between the lining of internal and external hemorrhoids?
Internal nodes are covered with rectal mucosa since they form proximal to the upper boundary of the anal canal. External nodes are located near the lower boundary and are covered with stratified squamous epithelium.
What is the typical microscopic picture in hemorrhoids?
On histological specimens stained with hematoxylin and eosin, the key morphological feature is pronounced cavernous transformation of venous vessels.
What else to study on this topic
- Anatomy of the valve apparatus of the portal vein and its branches.
- Histological structure of the rectal mucosa transition zone.
- Pathogenesis and morphology of hemorrhoidal thrombophlebitis.
- Mechanisms of cavernous transformation of venous vessels.
- Viral infections of the anorectal region (as a port of entry).
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