What Are Hemorrhoids?
Hemorrhoids are normal vascular structures in the anal canal consisting of connective tissue cushions with arteriovenous communications that contribute to anal continence and complete closure of the anal canal. 1 They become a disease only when they enlarge, prolapse, or thrombose, causing symptoms.
Anatomy and Normal Function
Hemorrhoids exist in the subepithelial space of the anal canal and consist of connective tissue cushions surrounding direct arteriovenous communications between terminal branches of the superior rectal arteries and the rectal veins 1. These cushions:
- Contribute 15-20% of resting anal pressure
- Serve as a conformable plug ensuring complete anal canal closure 1
- Are present from infancy as normal anatomical structures 1
- Most people have 3 cushions, though the typical configuration (right anterior, right posterior, left lateral) occurs only 19% of the time 1
Classification
Internal vs External Hemorrhoids
Hemorrhoids are classified as internal or external based on their position relative to the dentate line 1:
- Internal hemorrhoids: Located above the dentate line, covered by columnar epithelium
- External hemorrhoids: Located below the dentate line, covered by anoderm with somatic pain receptors
Grading System for Internal Hemorrhoids
The Banov classification system is used by the American Society of Colon and Rectal Surgeons 1:
- First-degree: Bleed but do not prolapse
- Second-degree: Prolapse with defecation but reduce spontaneously
- Third-degree: Prolapse and require manual reduction
- Fourth-degree: Cannot be reduced; usually include both internal and external components
Symptoms
Internal Hemorrhoids
- Bleeding: Bright red blood (due to arterial oxygen tension from arteriovenous communications) 1
- Prolapse: Tissue protruding from the anal canal
- Mucus discharge and soiling: Leading to perianal itching (pruritus ani) 1
- Generally painless unless thrombosed or incarcerated 1
External Hemorrhoids
- Usually asymptomatic unless thrombosed 1
- When thrombosed: Acute-onset severe anal pain with palpable perianal lump 1
- May bleed when local pressure causes erosion through overlying skin 1
Pathophysiology
Hemorrhoidal disease develops from abnormal swelling of anal cushions, stretching of suspensory muscles, and dilation of the submucosal arteriovenous plexus, resulting in prolapse of upper anal and lower rectal tissue 1. The tissue becomes easily traumatized, leading to bleeding.
Contributing factors (though not rigorously proven) include 1:
- Inadequate fiber intake
- Prolonged sitting on toilet
- Chronic straining at stool
- Constipation or diarrhea
- Pregnancy (0.2% require urgent hemorrhoidectomy for incarcerated prolapse)
Important Clinical Distinctions
What Hemorrhoids Are NOT:
- Hemorrhoids alone do not cause positive fecal occult blood tests 1
- Anemia from hemorrhoids is rare (0.5 patients/100,000 population) 1
- Anal pain suggests other pathology (fissure, abscess) unless thrombosis has occurred 1
- Portal hypertension varices are distinct from hemorrhoids and should not be treated with standard hemorrhoidal therapies 1
Common Pitfalls
Because many anorectal symptoms are incorrectly attributed to hemorrhoids, careful anorectal evaluation is warranted 1. Up to 20% of patients with hemorrhoids have concomitant anal fissures 1. Sharp postdefecatory pain suggests anal fissure, not hemorrhoids 1.
Epidemiology
The true prevalence is difficult to determine due to self-reporting and non-specific symptoms 1. Community-wide prevalence in the US is reported at 4.4%, with peak prevalence between ages 45-65 1. More recent data suggests approximately 10 million individuals in the US are affected 2.