16 Rectal bleeding

KEY POINTS
• Anorectal bleeding is characteristically bright red, associated with defaecation, not mixed with the stool and visible on toilet paperboften associated with other symptoms of anorectal disease.
• Distal (left-sided/sigmoid) bleeding is characteristically dark red, with clots, may be mixed with the stool.
• Proximal colonic or ileal bleeding is characteristically dark red, fully mixed with the stool or occultbunless heavy when it may appear as  ‘distal’ or ‘anorectal’ in type.
• In children, Meckel’s diverticulum, intussusception and ileal tumours are common causes.
• In young adults, colitis, Meckel’s diverticulum and haemorrhoids are common causes.
• In the elderly, neoplasia, diverticular disease and angiodysplasia are common causes.
Important diagnostic features
Small intestine
• Meckel’s diverticulum: young adults, painless bleeding, darker red/melaena common.
• Intussusception: young children, colicky abdominal pain, retching, bright red/mucus stool.
• Enteritis (infective/radiation/Crohn’s).
• Ischaemic: severe abdominal pain, physical examination shows mesenteric ischaemia or AF, few signs, later collapse and shock.
• Tumours (leiomyoma/lymphoma): rare, intermittent history, often modest volumes lost.
Proximal colon
• Angiodysplasia: common in the elderly, painless, no warning, often large volume, fresh and clots mixed.
• Carcinoma of the caecum: more often causes anaemia than PR bleeding.
Colon
• Polyps/carcinoma: may be large volume or small, ?associated change in bowel habit, blood often mixed with stool.
• Diverticular disease: spontaneous onset, painless, large volume, mostly fresh blood, previous history of constipation.
• Ulcerative colitis: blood mixed with mucus, associated with systemic upset, long history, intermittent course, diarrhoea prominent.
• Ischaemic colitis: elderly, severe abdominal pain, AF, bloody diarrhoea, collapse and shock later.
Rectum
• Carcinoma of the rectum: change in bowel habit common, rarely large volumes.
• Proctitis: bloody mucus, purulent diarrhoea in infected, perianal irritation common.
• Solitary rectal ulcer: bleeding post-defaecation, small volumes, feeling of ‘lump in anus’, mucus discharge.
Anus
• Haemorrhoids: bright red bleeding post-defaecation, stops spontaneously, perianal irritation.
• Fissure in ano: extreme pain post-defaecation, small volumes bright red blood on stool and toilet paper.
• Carcinoma of the anus: elderly, mass in anus, small volumes bloody discharge, anal pain, unhealing ulcers.
• Perianal Crohn’s disease.
KEY INVESTIGATIONS
• FBC: anaemiabtumours/chronic colitis.
• Clotting: bleeding diatheses.
• PR/sigmoidoscopy: anorectal tumours, prolapse, haemorrhoids, distal colitis.
• Abdominal X-ray: intussusception.
• Colonoscopy: diverticular disease, colon tumours, angiodysplasia.
• Angiography: angiodysplasia, small bowel causes (especially Meckel’s). (Needs active bleeding 0.5 ml/min, highly accurate when positive, invasive, allows embolization therapy.)
• Labelled RBC scan: angiodysplasia, small bowel causes, obscure colonic causes. (Needs active bleeding l ml/min, less accurate placement of source, non-invasive, non-therapeutic.)
• Small bowel enema: small bowel tumours.