Radiation Enteritis

Radiation enteritis is injury to the small bowel from therapeutic ionising radiation to the abdomen or pelvis, presenting acutely during treatment or chronically months to years later.

• Acute enteritis occurs in 50 to 75% during radiotherapy, from epithelial cell death and crypt loss.
• Chronic enteritis affects 5 to 15%, from endarteritis, submucosal fibrosis and ischaemia, with onset from 6 months to decades after treatment.
• Risk factors: dose over 45 Gy, large treatment volume, concurrent chemotherapy, prior abdominal surgery with adhesions, inflammatory bowel disease, diabetes, vascular disease, thin body habitus, smoking, collagen vascular disease.
• Complications: strictures, obstruction, fistulae, perforation, bleeding, bile acid malabsorption, bacterial overgrowth, malnutrition, vitamin B12 deficiency.

• Acute: nausea, vomiting, cramping, watery diarrhoea, tenesmus within 2 to 3 weeks of starting treatment.
• Chronic: diarrhoea and steatorrhoea, weight loss, abdominal pain, bloating, vomiting from partial obstruction, rectal bleeding, anaemia.
• Obstruction, fistula (enterovesical, enterocutaneous), peritonitis with perforation.
• Distinguish from tumour recurrence, which must be excluded in late presentations.

• Clinical diagnosis with treatment history.
• Blood tests: full blood count, albumin, B12, folate, iron studies, vitamin D, fat soluble vitamins, calcium, magnesium.
• Stool studies and C. difficile testing.
• Breath hydrogen testing for bacterial overgrowth, SeHCAT for bile acid malabsorption.
• CT or MR enterography: segmental bowel wall thickening, stricture, fistula, adhesions. Capsule endoscopy is avoided if stricture is suspected.
• Endoscopy or enteroscopy with biopsy (hyalinised submucosa, obliterative endarteritis) when diagnosis is uncertain. Exclude recurrent cancer with imaging.

Acute

• Loperamide 2 to 4 mg up to four times daily, hydration, low residue, lactose free diet, antiemetics (ondansetron 4 to 8 mg). Stop or interrupt radiotherapy if severe. Octreotide 100 to 150 micrograms SC three times daily for refractory secretory diarrhoea.

Chronic

• Treat bile acid diarrhoea: cholestyramine 4 g one to three times daily, or colesevelam 625 mg twice daily.
• Treat bacterial overgrowth: rifaximin 550 mg three times daily for 14 days, or rotating courses of metronidazole 400 mg three times daily.
• Dietary modification: low fat, lactose free, small frequent meals, medium chain triglycerides. Replace vitamins (hydroxocobalamin 1 mg IM every 3 months, vitamin D).
• Pancreatic enzyme replacement for steatorrhoea.
• Hyperbaric oxygen (30 to 40 sessions at 2.0 to 2.4 atmospheres) can help refractory bleeding and soft tissue injury.
• Parenteral nutrition for intestinal failure.
• Surgery for obstruction, fistula, perforation or intractable bleeding: resect the diseased segment with a well vascularised, non irradiated bowel anastomosis, as irradiated bowel heals poorly. Morbidity is high.
• Surveillance for recurrent cancer.