What Is Radiation Enteritis? How Is It Treated?

Radiation enteritis is an inflammatory bowel disorder caused by a combination of epithelial cell injury, microvascular changes, fibrosis, inflammation, and ischemia in gastrointestinal (GI) segments exposed to radiotherapy, particularly the jejunum and ileum.

It may be acute or chronic:

Acute Radiation Enteritis:

• develops during radiotherapy or within the first 3 months after treatment ends.
• Generally caused by impaired cell renewal and loss of the epithelial surface.
• May be reversible.

Chronic Radiation Enteritis:

• may appear months or years after radiotherapy.
• Characterized by permanent damage such as fibrosis, vascular narrowing, ischemia, luminal narrowing, fistulas, and adhesions.

Pathophysiology

Epithelial Cell Injury and Apoptosis:Ionizing radiation causes double-strand breaks in intestinal epithelial cells' genomic DNA. Basal crypt cells (Lgr5+ stem cells) are particularly vulnerable. When DNA repair is insufficient, cells undergo apoptosis or necrotic death. This impairs epithelial renewal and mucosal integrity and increases intestinal permeability.

Microvascular Dysfunction and Endothelial Injury: Radiation directly injures the intestinal microvascular endothelium, causing:

• Endothelial cell death
• Thrombosis
• Capillary obstruction and hypoperfusion
• Endarteritis obliterans (vascular lumen narrowing through fibrosis)

and, ultimately, local ischemia in the intestinal mucosa and submucosa.

Inflammatory Response and Cytokine Activation: After DNA injury and cell death, vascular endothelium and macrophages release proinflammatory cytokines:

• TNF-α, IL-1β, IL-6: initiate acute inflammation.
• TGF-β (Transforming Growth Factor-beta): causes fibroblast activation and extracellular matrix (ECM) accumulation in the chronic phase.
• NF-κB activation: increases gene expression sustaining chronic inflammation.

This results in mucosal edema, lymphocyte/macrophage infiltration, and mucosal ulceration.

Fibrosis Development: With persistent chronic inflammation, growth factors such as TGF-β and PDGF activate fibroblasts and initiate myofibroblast differentiation. These cells synthesize matrix proteins, including type I and III collagen and fibronectin, producing:

• Submucosal fibrosis
• Vascular lumen narrowing
• Luminal narrowing and strictures

among the resulting changes.

Neuronal Injury and Motility Disorders: Radiation may also affect the myenteric plexus and enteric neurons, reducing intestinal motility and causing spasms and abnormal transit time. This is particularly associated with chronic constipation and postprandial pain.

Microbiota Disruption and Bacterial Translocation: Radiation disrupts intestinal microbiota balance, causing dysbiosis. Lost mucosal integrity and increased permeability allow bacterial products (LPS, peptidoglycan, etc.) to enter circulation. This enhances the systemic inflammatory response and increases secondary infection risk.

What Are the Symptoms of Radiation Enteritis?

Symptoms of Acute Radiation Enteritis

(Usually during radiotherapy or within the first 3 months afterward.)

Symptoms in this phase result from direct radiation toxicity to mucosal cells and are often reversible:

• Watery diarrhea (the most common symptom)
• Abdominal cramps and colicky pain
• Nausea and vomiting
• Loss of appetite, weight loss
• Gas and abdominal bloating
• Tenesmus (the urge to empty the bowel but inability to pass stool)
• Mild rectal bleeding (rare, particularly with accompanying radiation proctitis)
• Fatigue and weakness

Symptoms generally worsen during radiotherapy and tend to subside within a few weeks after treatment ends.

Symptoms of Chronic Radiation Enteritis

(Develop months or years after radiation; associated with mucosal fibrosis and ischemic changes.)

The chronic form generally involves irreversible tissue injury, with symptoms prominently related to malabsorption and structural abnormalities:

• Chronic diarrhea (may be fatty or contain mucus)
• Weight loss and malnutrition (particularly deficiencies of vitamins A, D, E, K)
• Abdominal pain (particularly worsening after meals)
• Signs of bowel obstruction (vomiting, distension, reduced gas and stool passage — if a stricture is present)
• Rectal or occult gastrointestinal bleeding
• Fistulas (e.g., enterocutaneous, enterovaginal)
• Anal or perianal pain (with accompanying proctitis)
• Incontinence or stool leakage (if neural injury is present)
• Mineral deficiencies, including calcium, magnesium, and iron

What Determines Symptom Severity?

• Radiation dose and field
• Treatment duration and fractionation planning
• Concomitant chemotherapy
• Age, nutritional status, and coexisting conditions
• Intestinal microbiota and genetic susceptibility

How Is Radiation Enteritis Diagnosed?

Radiation enteritis is diagnosed using the patient's history, physical findings, and radiotherapy history, together with laboratory tests, imaging, and endoscopic assessment. Infections, inflammatory bowel diseases, and recurrent tumors must be excluded in the differential diagnosis.

Clinical History and Assessment

• Radiotherapy history: abdominal or pelvic radiotherapy (usually >45 Gy)
• Symptoms: diarrhea, abdominal pain, weight loss, fistulas, signs of obstruction
• Time of onset: acute (within the first 3 months) or chronic (months to years later)

Physical Examination Findings

• Abdominal tenderness
• Distension
• Signs of peritonitis or obstruction in advanced cases
• Anal/perianal fistula or scar tissue

Laboratory Tests

• Complete blood count: anemia (chronic blood loss), leukocytosis (if infection is present)
• CRP, ESR: nonspecific inflammatory markers
• Electrolyte panel: hypokalemia, hypomagnesemia due to malabsorption
• Iron, B12, vitamin D levels: for chronic malabsorption
• Stool tests: fecal leukocytes or calprotectin as inflammatory markers
• Stool culture/parasite testing: exclude infection
• Fecal blood testing: for occult bleeding

Imaging Methods

CT (Computed Tomography) or MR Enterography

• Segmental wall thickening
• Mucosal edema and contrast enhancement
• Strictures, fistulas, and perforation may be detected.
• A "target sign" or "halo sign" may be seen.

Ultrasonography (US)

• Intestinal wall thickness
• Reduced peristalsis
• Free fluid or fistulas may be seen
• Fluoroscopic examinations (e.g., barium studies)
• Location and length of chronic strictures
• Transit time assessment

Endoscopic Examination

Colonoscopy / Sigmoidoscopy

• Acute phase: mucosal edema, erythema, ulceration
• Chronic phase: mucosal atrophy, telangiectasia, strictures
• Radiation proctitis findings if the rectum is involved
• Biopsy: supports diagnosis (fibrosis, atrophic crypts, endarteritis obliterans)

Capsule Endoscopy

• Useful for noninvasive assessment of small bowel mucosa
• Contraindicated if a stricture is suspected (the capsule may become trapped)

Histopathology (Biopsy)

• Mucosal atrophy, crypt loss
• Submucosal fibrosis
• Endarteritis obliterans (vascular lumen narrowing)
• Chronic inflammatory cell infiltration (lymphocytes, macrophages)
• Telangiectatic vessels

Conditions to Exclude in the Differential Diagnosis

• Infectious enterocolitis (C. difficile, Giardia, CMV, etc.)
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• Recurrent malignancy or metastasis
• Drug-induced enteritis (NSAIDs, chemotherapy)

Treatment of Radiation Enteritis

The main treatment goals are controlling inflammation, reducing malabsorption, relieving symptoms, and preventing complications.

Care should be multidisciplinary, with gastroenterology, radiation oncology, surgery, and nutrition teams working together.

Treatment of Acute Radiation Enteritis

This phase is generally reversible, and treatment is supportive.

Diet and Supportive Measures

• Lactose-free, low-fiber, fat-free diet
• Fluid and electrolyte balance (particularly with diarrhea)
• Intravenous hydration if needed

Diarrhea Control

• Loperamide (2–4 mg initially, then 2 mg after each stool, maximum 16 mg/day)
• Diphenoxylate + Atropine (refractory cases)

Analgesia and Antispasmodics

• Mild: Paracetamol
• Moderate–severe: Opioids (e.g., tramadol)
• Bowel spasms: Hyoscine-N-butylbromide (Buscopan)

Radiotherapy Adjustment

• Review the radiation dose or fractionation plan.
• Temporarily interrupt treatment if needed.

Treatment of Chronic Radiation Enteritis

Permanent structural changes make treatment more difficult in this phase, often requiring combined approaches.

Diet and Malabsorption Management

• For malabsorption: vitamins A, D, E, K, iron, B12, and folate supplementation
• Elemental diet (predigested nutrients)
• Parenteral nutrition (severe malnutrition)

Anti-inflammatory and Immunosuppressive Treatments

• Sulfasalazine or mesalazine (topical anti-inflammatory effect)
• Corticosteroids (oral budesonide or systemic prednisone — limited duration)
• Immunosuppressants such as azathioprine (rarely, refractory cases)

Antibiotics

For small intestinal bacterial overgrowth (SIBO): rifaximin, metronidazole, ciprofloxacin

Antioxidants / Mucoprotective Agents (Experimental / Supportive)

• Sucralfate: forms a protective layer over the mucosa
• Glutamine: may support intestinal epithelial regeneration
• Pentoxifylline + Vitamin E: suggested in some studies for their antifibrotic effect.

Managing Complications of Radiation Enteritis

Intestinal Narrowing (Stricture) and Obstruction: Radiation may stiffen and narrow the intestinal wall, causing abdominal pain after meals, bloating, and difficulty passing gas and stool.

Treatment: endoscopic balloon dilation may widen the stricture. If needed, the narrowed segment is removed surgically. Nutritional support is provided.

Fistula (an Abnormal Opening Between the Bowel and Another Organ): radiation can create small passages from the bowel to the outside, vagina, or bladder. Stool or gas may then pass from abnormal locations.

Treatment: control infection and maintain fluid balance. Surgery may be needed if it does not close on its own.

Intestinal Bleeding: radiation may weaken intestinal blood vessels, leading to fresh blood in stools or black stools.

Treatment: medicated enemas (e.g., sucralfate) may be used. Bleeding areas can be cauterized endoscopically. Transfusion or angiography may be needed.

Bowel Perforation: rare but serious. If the intestinal wall ruptures, stool can leak into the abdomen and emergency surgery may be required. It presents with sudden abdominal pain and fever.

Treatment: emergency surgery is necessary, followed by antibiotics and fluid treatment.

Malnutrition and Weight Loss: radiation may prevent the bowel from absorbing nutrients, causing weight loss, diarrhea, and vitamin deficiencies.

Treatment: a special diet (easily digested foods), with vitamin, mineral, and fluid supplementation if needed. Those unable to eat adequately may receive nutrients intravenously.

Recurrent Bowel Inflammation: some patients develop recurrent inflammation, particularly in the rectum (the final part of the large bowel).

Treatment: anti-inflammatory enemas, certain antibiotics, and endoscopic cauterization of the inflamed area.

Measures to Prevent Radiation Enteritis

• Use Modern Radiotherapy Techniques: technologies such as IMRT (Intensity-Modulated Radiotherapy), IGRT, and proton therapy allow more precise beam delivery, reducing radiation dose to the bowel.
• Individualize Treatment Planning: simulation and imaging before radiotherapy aim to protect the bowel. Radiation specialists determine the most appropriate beam direction and dose.
• Keep the Bowel Empty During Treatment: a full bowel may receive more radiation. Light eating, an antidiarrheal diet, and enemas if necessary may therefore be recommended on treatment days.
• Bowel-Protective Drugs May Be Used: some patients may use sucralfate, glutamine, propolis, or vitamin E + pentoxifylline on medical advice. These may protect the mucosa and reduce injury (potentially supportive, although evidence is limited).
• Nutritional Support and Preserving Bowel Health: choose low-fiber, low-fat, easily digested foods during treatment. Drink plenty of water and avoid gas-producing foods. Consult a nutrition specialist if needed.
• Stop Smoking and Alcohol Completely:smoking and alcohol increase radiation injury by making intestinal mucosa more sensitive.
• Control Coexisting Conditions: diabetes, vascular disease, or connective tissue disease may worsen radiation injury. Treat these beforehand and keep them controlled.
• Extra Caution with Chemotherapy: some drugs given with radiotherapy (e.g., 5-FU, cisplatin) may increase intestinal injury. Dose adjustments and protective measures require extra care.