Inflammatory bowel disease–like conditions: radiation injury of the gut

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Introduction

Gastrointestinal (GI) tract is vulnerable to radiation injury, consisting acute and chronic forms. The acute injury exerts cytotoxic effect on the fast dividing intestinal epithelium, particularly intestinal stem cells, with subsequent changes in cell death. Downregulation of Bcl-2 plays a central role. The disruption of intestinal epithelial barrier may lead to bacterial translocation . Acute radiation injury is usually reversible . Chronic radiation injury is characterized by epithelial atrophy, fibrosis, and ischemia resulting from obliterative arteritis and stem cell death . The latter one is more common than the previous.

Risk factors consist of the elements related to patients (such as previous abdominal or pelvic surgery, low body weight, advanced age, female gender, tobacco use, diabetes, and cardiovascular disease) and therapies (such as dosage and interval). Since the majority of patients with chronic disease and a portion of ulcerative colitis (UC) have to undergo various operations in the lifetime, surgery-associated adhesion may result in fixed bowel loops, posing a risk for radiation injury. The group of authors reported that prior pelvic radiation for colitis-associated cancer increased the risk for pouch failure after restorative proctocolectomy .

Common histologic features in acute and chronic radiation injury include epithelial injury, crypt distortion, Paneth cell metaplasia, intramucosal hemorrhage, dilated, tortuous capillaries, hyalinization, and fibrosis of the lamina propria and submucosal area, and microthrombi ( Fig. 22.1 ) . The injury can be superficial or transmural, resulting in specific inflammation and fibrosis. Radiation enteritis, colitis, or proctitis can mimic inflammatory bowel disease (IBD) in clinical, endoscopic, and radiographic presentations .

Clinical history makes differential diagnosis between radiation injury to the GI tract and IBD straightforward, despite having shared endoscopic features between the disease entities. However, clinical scenarios of IBD, IBD-associated cancer, IBD patients undergoing radiation therapy for non-GI malignancy, and IBD versus radiation–associated anastomotic lesions, may overlap. Although the injury from external beam radiation accounts for the majority of patients, brachytherapy can also cause radiation injury to the bowel .