Injury to the intestines can occur following radiation therapy for cancer. It can affect both the large and small intestine, is often progressive, and may lead to a variety of clinical consequences (such as diarrhea, nausea, weight loss, abdominal pain, intestinal obstruction, and perforation) depending upon the extent of the injury. It usually develops six or more months after radiation therapy. This contrasts with the timing of acute radiation enteritis (characterized by diarrhea and abdominal pain), which develops during or shortly after radiation therapy and resolves within two to six weeks after completion of treatment.
Chronic radiation enteritis is due to an obliterative arteritis that leads to intestinal ischemia, which can result in stricture, ulceration, fibrosis, and occasionally fistula formation. The physiologic consequences can include altered intestinal transit, reduced bile acid absorption, increased intestinal permeability, bacterial overgrowth and lactose malabsorption. Clinical manifestations may include nausea, vomiting, lactose intolerance, obstructive symptoms, diarrhea, weight loss, malnutrition, and bleeding (usually in patients with colonic involvement).
This topic review will focus on the diagnosis and management of chronic radiation injury to the small intestines and proximal colon. The pathogenesis, clinical manifestations, and risk factors associated with radiation enteritis, along with the prevention and treatment of chronic radiation proctitis, are presented separately. (See "Gastrointestinal toxicity of radiation therapy", section on 'Radiation enteritis' and "Clinical manifestations, diagnosis, and treatment of radiation proctitis".)
The diagnosis is usually established by suggestive radiologic findings in patients with compatible clinical features who have a history of prior radiation exposure. The patient's previous radiation treatment record should be reviewed to determine the total dose and distribution of the radiation field. This may help to determine which intestinal segments may have received excessive radiation exposure, information that can be correlated with the radiologic findings and the clinical presentation.
We usually obtain an abdominal CT scan followed by an upper gastrointestinal series with small bowel follow through in patients with suspected small bowel disease. Additional imaging is reserved for patients in whom the diagnosis remains unclear. We generally perform a colonoscopy in patients with suspected colonic involvement.