Classification of radiation enteritis

Classify as acute (during treatment) or chronic (>18 months post-treatment)

Risk factors

High-dose radiotherapy (>5000cGy)
Previous abdominal surgery (adhesions - higher risk with laparotomy)
Pre-existing vascular disease
HTN
Diabetes
Adjuvant treatment with certain chemotherapeutic agents (5-FU, doxorubicin, dactinomycin, MTX)
Fixed locations are highest-risk for injury: TI, caecum, rectum
Development of acute symptoms is a risk factor for development of chronic symptoms, but not necessary

Pathophysiology

Acute
- Free radicals causing direct inflammation
- Effects seen within hours - leucocyte infiltration, ulceration
Subsequent effects
- Most important effect of acute injury is to damage mucosal stem cells, which leads to a long-term reduction in cellular reserves for intestinal villi. Mucosal denudation occurs, with shortened villi and decreased absorptive area.
- Progressive obliterative vasculitis, and collagen deposition and fibrosis in submucosa
- Small bowel becomes thickened due to chronic inflammation and ischaemia
- Telangiectasias can be present due to disordered revascularisation, causing bleeding
Chronic outcomes on bowel function
- End up with impaired normal absorption and transit - particularly B12 and bile salts due to impact on ileum, and subsequent bile salt diarrhoea
- Commonly leads to strictures with obstructive symptoms, or small bowel fistulas
- Risk of malignancy as a late consequence of radiation injury

Acute radiation enteritis

Presentation

Normally starts during third week of treatment, and resolves 2-6 weeks after completion
Diarrhoea
Cramping pain
Minor bleeding
Nausea
Faecal urgency

Management

ACE inhibitors and statins may reduce acute GIT symptoms during radical pelvic radiotherapy
Supportive treatment - antimotility agents, antispasmodics and avoidance of dehydration
Typically self-limiting, resolving within a few weeks
Loperamide usually works well

Chronic radiation enteritis

Presentation

Typically develops from 18 months 6 years after treatment, but can take up to 30 years
Malabsorption
- Diarrhoea/steatorrhoea/weight loss/nutritional
- Loss of bile salts - cholestyramine may be helpful
Disordered motility - from fibrosis, or from true mechanical obstruction in areas of chronic stricture
- CT or MR enterography useful in identifying strictures
- Avoid pillcam due to high risk of pill trapping

Management

Indications for surgery (very uncommon):
- Obstruction - adhesional vs strictures
- Perforation
- Fistulisation
- Severe bleeding
Perioperative:
- Assess nutritional status
- Decompress with NGT
- Control sepsis
Surgery:
- Avoid extensive adhesiolysis - obstruction caused by rigid fixed loops in the pelvis is best bypassed
- Drain intra-abdo collections
- If resection and anastomosis is required, use diverting stoma, and ensure at least one end of the anastomosis is from outside the irradiated field
- Bypass may be easier than resection and anastomosis

Radiation proctitis

Common acutely, and generally resolves shortly after completion of therapy
Chronically - relates to histologic changes of progressive fibrosis and disordered revascularisation
- Diarrhoea/urgency/incontinence from fibrosis
- Telangiectasias result in bleeding
  - Evaluation:
    - Flexi sig - consider recurrence cancer, especially if >3 years since treatment, but avoid deep biopsies. Visual appearance of bowel is not a good indicator of severity of disease.
  - Treatment
    - Optimise bowel function by treating constipation or diarrhoea
    - Sucralfate enemas - effective, likely to improve bleeding and tenesmus
      - See proctitis topic
    - Hyperbaric oxygen is a POTENTIAL therapy
    - Severe bleeding -
    - For minor bleeding: not recommended by UTD, but some sources suggest apply 4% or 10% formalin solution via a long cotton-tipped applicator through rigid proctoscope. 4% formalin can be instilled directly into rectum in 50mL aliquots or on formalin-soaked gauze, then removed after 2-3 minutes followed by saline irrigation, ensuring protection of perianal skin, can be done biweekly.
    - Endoscopic - bipolar for individual vessels, APC for more diffuse. Repeat treatment may be necessary.
    - APC and formalin have been found to be equally efficacious in refractory bleeding from chronic radiation proctitis, but formalin does carry risk of complications including necrosis and fistulisation.
    - Surgery is rarely required <1% - in severe uncontrollable haemorrhage, an APR or inter-sphincteric proctectomy may be required.
- Fistulae
  - Management dependent on location, timing, state of surrounding tissue, and overall condition.
  - Similar principles to non-radiated patients with fistulae - but harder to dissect it out due to poor tissue
  - Mid to upper rectal fistulae - resection with anastomosis of healthy, nonradiated colon to distal rectum or anal canal
  - Low rectal fistula to vagina or prostatic urethra - various approaches - abdominal, perineal, trans-sacral, trans-sphincteric. Need to divert before reconstruction. Need to use a graft (omentum/rectus/gracilis/buccal mucosa/labial fat pad). Diversion alone (colostomy + SPC) may be offered to some patient. Need to exclude recurrent malignancy prior to repair.