Etiology and Pathogenesis
The condition begins with dysfunction of the valve apparatus of the portal vein and its branches, specifically the rectal veins. When the valves fail to function properly, localized hydrostatic pressure increases. As a result of this pressure, the vascular walls weaken, and the vessels prolapse (bulge) into the lumen of the anal canal as spherical masses.
The exact etiology of this process remains partially understood. However, clinicians identify several clear predisposing factors. These include:
- Chronic constipation.
- Repeated pregnancies.
- Strenuous physical exertion (heavy lifting).
- Alcohol abuse.
All of these conditions contribute to blood stasis and elevated pressure within the venous system.
Anatomy and Classification
Hemorrhoids do not form randomly; they develop strictly in the areas where normal cavernous venous plexuses reside. Anatomically and morphologically, there are two main types of hemorrhoids, depending on which venous plexus is affected:
- Internal hemorrhoids. Develop from the internal hemorrhoidal plexus (a cluster of cavernous veins) located proximal to the dentate line (upper boundary of the anal canal). In this transition zone, the rectal mucosa shifts into the stratified squamous epithelium of the anal canal. Accordingly, internal hemorrhoids are always covered by rectal mucosa.
- External hemorrhoids. Form from the external hemorrhoidal plexus. This plexus is located near the lower margin of the anal canal, in the zone where stratified squamous epithelium firmly adheres to underlying tissues. Therefore, external hemorrhoids are covered by stratified squamous epithelium.
Morphology and Clinical Features
Despite their different locations, both venous plexuses share a similar basic structure. Morphologically, they consist of dilated veins directly fed by small, interlacing arterioles. This anatomical feature is of paramount clinical importance: due to constant arterial inflow, bleeding from damaged hemorrhoidal veins frequently exhibits the characteristics of arterial bleeding (bright red blood).
As the pathology progresses, the cavernous vascular spaces gradually enlarge. They transform into distinct hemorrhoidal nodes that prolapse into the upper anal canal.
On microscopic examination of an excised node (e.g., in external hemorrhoids) using standard hematoxylin and eosin staining, cavernous transformation of the venous vessels is clearly visualized.
Complications
If left untreated, the condition inevitably leads to severe complications. Two main clinical scenarios develop:
- Mechanical trauma. Injury to enlarged and thinned vascular nodes (e.g., during the passage of hard stools) leads to profuse bright red bleeding.
- Infection. The anorectal region frequently serves as an entry portal for pathogens. Infection of the cavernous spaces triggers an inflammatory response, leading to a severe complication—hemorrhoidal thrombophlebitis.