Pathology of the Colon, Rectum and Anus

• Colon pathologies


  • Congenital anomalies
  • Intestinal fistulae
  • Diverticular disease
  • Inflammatory bowel disease
  • Volvulous
  • Polyps
  • Cancer
• Anorectum pathologies


  • Congenital anomalies
  • Prolapse
  • Fissures
  • Haemorrhoids
  • Tumours and Malignancies

  
• Intestinal fistulae


  Abnormal connection between two body parts, causing faecal material to exit through an opening other than the anus
• 80% of intestinal fistulae occur after surgery
• Causes of remaining 20% of intestinal fistulae


  • Congenital anomalies
  • Abdominal trauma
  • Inflammatory conditions
  • Malignant tumours

  
• Diverticular disease


  Outpouching of the colonic mucosa through the circular muscle layer
• Sigmoid colon is the most commonly affected by diverticular disease

  
• Aetiology of diverticular disease


  1. Lack of fibre diet

  2. Chronic constipation

  3. Increase in intraluminal pressure

  4. Diverticulosis
• Complications of diverticular disease


  • Acute diverticulitis
  • Perforation
  • Recurrent attacks of acute inflammation
  • Colonic strictures
  • Fistula formation

  
• Inflammatory bowel diseases


  Usually denotes ulcerative colitis and Crohn disease

  
• Other known causes of inflammatory bowel disease


  • Schistosoma
  • Ameobic colitis
  • Tuberculosis
  • Typhoid enteritis

  
• Aetiology of ulcerative colitis and Crohn disease is not clear

  
• Volvulus


  When a loop of intestine twists around itself and the mesentery that supplies it, causing a bowel obstruction
• Causes of volvulus


  • Midgut volvulus (usually in babies with congenital intestinal malrotation)
  • Segmental volvulus (people of any age with abnormal intestinal contents or adhesions)
  • Volvulus of the cecum, transverse colon, or sigmoid colon (usually in adults with redundant intestinal tissue and constipation)

  
• Polyps


  Small growths, usually benign and with a stalk, protruding from a mucous membrane
• Risk factors for colon and rectal carcinoma


  • Neoplastic adenomas
  • Familial adenomatous polyposis coli (APC)
  • Ulcerative colitis
  • Lack of fibre and high fat diet
  • Utero-colic anastomosis

  
• Adenocarcinoma


  The most common histologic type of colon and rectal carcinoma
• Two-thirds of colon and rectal carcinomas are in the rectum and sigmoid

  
• Modes of spread for colon and rectal carcinoma


  • Direct contiguity
  • Lymphatic
  • Blood
  • Transperitoneal
• Congenital abnormalities of the anorectal canal


  • Imperforate anus
  • Anal stenosis
  • Membrane covering
  • Anorectal agenesis
  • Rectal atresia

  
• Risk factors for rectal prolapse


  • Chronic constipation
  • Straining to pass bowel motions
  • Weakened pelvic floor muscles
  • Weakened anal sphincter muscles
  • Weakening of the muscles associated with ageing
• Fissure-in-ano


  Longitudinal ulcer in the distal part of the anal canal
• Aetiology of fissure-in-ano is unknown, but may be related to the passage of hard stools
• Haemorrhoids


  Dilated rectal venous plexus with internal and external components
• Causes of haemorrhoids


  • Hereditary (weakness of the vein walls)
  • Constipation, straining stools
• Complications of haemorrhoids


  • Bleeding
  • Thrombosis
  • Inflammation
  • Perianal abscess and fistula

  
• Majority of perianal abscesses and fistulae originate in the intersphincteric spaces from the infected glands
• Anal tumours


  Associated with human papillomavirus (HPV)
• Annual incidence of anal tumours is 1%
• HPV in the genital area is considered the most common sexually transmitted disease, with prevalence believed to exceed 50%
• Highest prevalence and risk of anal tumours is in the second and third decades
• Anal tumours associated with HPV


  • Anal dysplasia / CIS
  • Verrucous carcinoma
  • Squamous cell carcinoma / basaloid carcinoma
• Anal tumours - malignancies


  Commonly squamous cell carcinoma
• Risk factors for anal malignancies


  • HPV infection
  • HIV with low CD4 count
  • Cigarette smoking
  • Immune suppression
  • Anal warts
• Adenocarcinoma of the anus often originates from the rectum