Colon

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• Acute radiation colitis (< 6 months after radiation treatment):
  • Epithelium can contain:
    • Reduced mitotic activity
    • Apoptosis
    • Reduced goblet cell mucin
    • Goblet cell swelling
    • Degenerative changes
    • Atypia (nuclear enlargement and malorientation)
  • Inflammation
    • Typically eosinophilic (characteristic)
      • Lamina propria eosinophilic infiltration
      • Eosinophilic cryptitis
      • Eosinophilic crypt abscesses
  • Can be fibroblast proliferation in lamina propria (reactive changes to radiation)
• Chronic radiation colitis (> 6 months after radiation treatment):
  • Epithelium:
    • Paneth cell metaplasia
    • Ulceration
    • Mild epithelial atypia
  • Crypts:
    • Architectural changes and atrophy
  • Lamina propria:
    • Fibrosis
    • Mild chronic inflammation
    • Atypical fibroblasts / stromal cells with enlarged hyperchromatic nuclei
  • Submucosa and deeper layers:
    • Vasculature
      • Hyalinization and fibrosis of vessel wall
      • Intimal thickening
      • Vascular ectasia or narrowing
      • Thrombosis
      • Endothelial cell atypia
• Reference: Am J Surg Pathol 2002;26:498

Contributed by Maryam Kherad Pezhouh, M.D., M.Sc.

A 76 year old woman with a history of cervical cancer status post stereotactic radiation presents 7 months later with spotty rectal bleeding. Colonoscopy reveals erythema, which is biopsied. Histology demonstrates lamina propria fibrosis and mild chronic inflammation; the epithelium shows focal mild crypt architectural distortion and ectatic vessels. No significant activity was found. What is the most appropriate diagnosis?

1. Inflammatory bowel disease
2. Ischemia
3. Metastatic cervical cancer, direct extension
4. Radiation colitis

D. Radiation colitis. Chronic radiation colitis usually presents later than 6 months and has the following histological changes that are secondary to vascular damage: epithelium with Paneth cell metaplasia, ulceration, mild atypia, crypt architectural distortion, lamina propria fibrosis, mild chronic inflammation and atypical fibroblasts with enlarged nuclei. Vascular changes, such as hyalinization and fibrosis of vessel wall, intimal thickening, vascular ectasia and endothelial cell atypia, can be seen in the submucosa. Inflammatory bowel disease (answer A) presents with active chronic colitis pattern of injury. The absence of activity is not a typical feature of emerging inflammatory bowel disease. Although radiation can also induce ischemia (answer B), features of radiation should be absent (example: atypical fibroblasts and hyalinization of lamina propria). Direct extension of cervical cancer (answer C) would show squamous cell carcinoma invading submucosal. The endoscopic findings would also likely show luminal narrowing secondary to mass effect, rather than a small ulcer.

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Reference: Radiation enterocolitis

A 60 year old man with a prior history of prostate adenocarcinoma status postradiation 5 years ago presents with severe sigmoid colon stricture. The patient underwent a partial colonic resection and a section of the colonic wall is shown. What is the most likely diagnosis?

1. Collagenous colitis
2. Infection
3. Mucosal prolapse
4. Radiation colitis, acute
5. Radiation colitis, chronic

E. Radiation colitis, chronic. Chronic radiation colitis is expected at > 6 months postradiation therapy. Sections show ulcerations, mild epithelial atypia, architectural changes and atrophy. The lamina propria contains fibrosis, mild chronic inflammation and fibroblast atypia (enlarged hyperchromatic nuclei). The vasculature within submucosal and deeper layers contains hyalinization of vessel wall and intimal thickening. Vascular ectasia, narrowing and thrombosis can also be present. Collagenous colitis (answer A) typically presents with history of watery diarrhea and a > 10 μM subepithelial collagen table (collagenous band). Infection (bacterial) (answer B) will present with an acute clinical history (example: diarrhea and vomiting) after an inciting event (example: food consumption, travel). Acute colitis and granulomas can sometimes be seen. Viral infections (example: cytomegalovirus, Epstein-Barr virus) can occur in immunocompromised patients (example: HIV or transplant) and will contain atypical cells with nuclear changes. Mucosal prolapse (answer C) can present endoscopically as a polyp and contains ingrowth of thick muscle bundles that can mechanically squeeze ensnared epithelium. This is accompanied by variable inflammation, ulceration and reaction epithelial change. Acute radiation colitis (answer D) is expected at < 6 months postradiation therapy. The inflammation is typically eosinophilic (characteristic) with eosinophilic cryptitis, crypt abscesses and lamina propria eosinophilia. Sections demonstrate reduced mitotic activity, apoptosis, reduced goblet cell mucin, goblet cell swelling, degenerative changes and atypia (nuclear enlargement and malorientation).

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Reference: Radiation enterocolitis