Etiology

• Excessive straining (e.g., from chronic constipation, frequent bowel movements, chronic cough, heavy lifting, benign prostatic hyperplasia)

• Extended periods of sitting (e.g., due to occupation or sedentary lifestyle)

• Pregnancy

• Older age

• Connective tissue disorder (e.g., Ehlers‑Danlos syndrome, scleroderma)

• Anal cushions

  • Areas of thickened anal mucosa that consist of arteriovenous blood vessels (corpus cavernosum recti), smooth muscle (e.g., Treitz muscle), and fibroelastic tissue (e.g., collagen, elastic fibers)

  • Located at 11, 7 and 3 o'clock in the lithotomy position (right anterior, right posterior, and left lateral position)

  • Play an important role in maintaining continence by enabling tight closure of the rectum

  • Defecation causes contraction of supportive structures (e.g., Treitz muscle) → compression of anal cushions → increased diameter of the anal canal for adequate passage of stool

• Anal columns: longitudinal folds of mucous membrane that are fused at their inferior ends by transverse folds (anal valves)

• Anal sinuses: small, mucus-secreting pouches between the anal columns above the anal valves

• Dentate line

  • Circular separation line formed by the fusion of anal valves (hindgut-proctodeum junction)

  • Divides anal canal into an upper and lower part (also see characteristics of the anal canal above and below the dentate line below)

• External anal sphincter

  • Composed of

    • Subcutaneous external sphincter: surrounds lower third of anal canal

    • Superficial external sphincter

    • Deep external sphincter

  • Consists of skeletal muscle and functions to open and close the anal canal and opening

  • Innervated by the pudendal nerve and under voluntary control

• Internal anal sphincter

  • Surrounds upper two-thirds of anal canal

  • Consists of involuntary circular smooth muscle and is responsible for ∼ 85% of the resting pressure of the anal canal

  • Innervated by the enteric nervous system

• Prolapse of internal hemorrhoids, with possible incarceration and strangulation, may cause pain by triggering an anal sphincter complex spasm. → possible ischemia and necrosis of internal hemorrhoids → worsening anal sphincter complex spasm → potential external hemorrhoid thrombosis → cutaneous pain

• Develop above the dentate line, which is not innervated by cutaneous nerves; distension does not cause pain.

• Bleeding and/or prolapsed internal hemorrhoids irritate sensitive perianal skin → perianal itching

• Develop below the dentate line, which is innervated by cutaneous nerves; distention of this innervated skin due to thrombosis results in severe pain.

• Acute thrombosis triggers cutaneous pain, lasting 7–14 days → thrombosis resolves → residual skin or skin tags of distended anal skin

Hemorrhoids are not varicose veins (dilated, tortuous veins). Anorectal varices occur, e.g., as a result of portal hypertension. The terms anorectal varices and hemorrhoids are often used interchangeably, but this is incorrect.

• Often painless, bright red bleeding at the end of defecation

• Perianal mass in the event of prolapse

• Pruritus

• Anal discharge (containing mucus or fecal debris)

• Ulceration (in hemorrhoid stage IV)

• Manifestations are similar to those of internal hemorrhoids (i.e., bright red bleeding, pruritus, perianal mass)

• A thrombosed external hemorrhoid manifests with severe perianal pain and a tender perianal mass.