Aetiology

The primary aetiology is believed to be excessive straining due to either chronic constipation or diarrhoea. Repetitive or prolonged straining causes downward stress on the vascular haemorrhoidal cushions, leading to the disruption of the supporting tissue elements with subsequent elongation, dilation, and engorgement of the haemorrhoidal tissues.[1][8] Other conditions can contribute to the formation of haemorrhoids: an increase in intra-abdominal pressure can be caused by pregnancy or ascites; the presence of space-occupying lesions within the pelvis may cause a concomitant decrease in vascular return and increase in anal vascular engorgement.[9]

Pathophysiology

Haemorrhoids are a normal anatomical and functional component of the anal canal; they become pathological and are termed haemorrhoidal disease only when they cause symptoms. As the patient strains at stool, the haemorrhoids are pulled lower into the anal canal. As the vascular cushions engorge, the thin epithelial lining is easily torn, which causes bleeding. This is commonly seen as bright blood on cleansing, but can also be seen in the bowl. The haemorrhoids can enlarge to the point that they protrude from the anal canal and can cause a sensation of incomplete evacuation or require manual reduction following a bowel movement.[1]

External haemorrhoids commonly cause symptoms of pruritus or a feeling of inadequate cleaning following a bowel movement. These haemorrhoidal tissues can also become engorged and clots can form, causing a thrombosed external haemorrhoid. This is commonly preceded by a period of excessive straining. The patient experiences the sudden onset of perianal pain and a tender palpable lesion forms adjacent to the anal canal on the anal margin.

Classification

External haemorrhoids

Haemorrhoids that are located in the distal anal canal, distal to the dentate line, and covered by sensate anoderm or skin.[1]

Internal haemorrhoids (grade 1 to 4)

Haemorrhoids that originate proximal to the dentate line and are covered by insensate transitional epithelium.

  • Grade 1 - protrusion is limited to within the anal canal.

  • Grade 2 - protrudes beyond the anal canal but spontaneously reduces on cessation of straining.

  • Grade 3 - protrudes outside the anal canal and reduces fully on manual pressure.

  • Grade 4 - protrudes outside the anal canal and is irreducible.

This grading of internal haemorrhoids is only a reflection of the degree of prolapse but is not a measure of either the disease severity or of the size of haemorrhoidal prolapse.[1][2]​​

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