Definition/General
Introduction:
Radiation colitis is iatrogenic inflammatory condition resulting from therapeutic radiation exposure
Shows acute and chronic phases
Dose-dependent injury with characteristic histologic changes
Most common in pelvic radiation for gynecologic or prostate cancers.
Origin:
Results from ionizing radiation damage to colonic tissues
Causes DNA damage and free radical formation
Shows endothelial injury and vascular damage
Leads to fibroblast activation and chronic inflammation
Progressive tissue injury over time.
Classification:
Acute radiation colitis (within weeks of therapy)
Chronic radiation colitis (months to years later)
Early delayed effects (weeks to months)
Late delayed effects (years)
Radiation proctitis (rectal involvement).
Epidemiology:
Common in patients receiving pelvic radiotherapy
Dose-dependent incidence
Higher risk with >45 Gy
Age-related susceptibility
Combined modality therapy increases risk
Growing recognition with increased cancer survivorship.
Clinical Features
Presentation:
Acute phase: diarrhea, urgency, tenesmus during radiation
Chronic phase: rectal bleeding, strictures, obstruction months to years later
Pelvic pain
Fecal incontinence
Weight loss.
Symptoms:
Bloody diarrhea (most common chronic symptom)
Urgency and frequency
Tenesmus
Abdominal cramping
Mucus passage
Iron deficiency anemia.
Risk Factors:
Pelvic radiotherapy (gynecologic, prostate, rectal cancers)
Radiation dose >45 Gy
Large treatment volumes
Advanced age
Previous abdominal surgery
Concurrent chemotherapy.
Screening:
Colonoscopy (mucosal assessment)
CT scan (complications)
Barium studies (strictures)
Clinical correlation with radiation history
Exclude malignancy.
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Gross Description
Appearance:
Acute phase: mucosal erythema, edema, superficial ulceration
Chronic phase: pale, atrophic mucosa, telangiectasia, strictures
Friable mucosa
Loss of normal fold pattern
Stenosis and adhesions.
Characteristics:
Mucosal pallor
Prominent telangiectasia
Submucosal fibrosis
Wall thickening
Stenotic segments
Easy bleeding
Cobblestone appearance.
Size Location:
Rectosigmoid (most common - pelvic radiation)
Field-dependent distribution
Sigmoid colon
Small bowel involvement (ileum)
Dose-gradient effects.
Multifocality:
Radiation field distribution
Dose-dependent severity
Skip areas outside radiation field
Progressive changes
Late complications (strictures, fistulas).
Microscopic Description
Histological Features:
Acute phase: mucosal necrosis, inflammation
Chronic phase: atypical fibroblasts, vascular changes, fibrosis
Bizarre stromal cells
Telangiectasia
Hyalinized blood vessels.
Cellular Characteristics:
Atypical fibroblasts (enlarged, hyperchromatic nuclei)
Bizarre stromal cells
Radiation atypia in epithelium
Endothelial swelling
Foam cells
Chronic inflammatory cells.
Architectural Patterns:
Crypt distortion
Surface ulceration
Submucosal fibrosis
Vascular sclerosis
Smooth muscle atrophy
Neural changes.
Grading Criteria:
Acute: epithelial necrosis, acute inflammation
Subacute: epithelial atypia, early fibrosis
Chronic: fibrosis, vascular changes, atypical fibroblasts
Severity correlates with dose and time.
Immunohistochemistry
Positive Markers:
Smooth muscle actin (myofibroblasts)
CD31 (endothelial cells)
Factor VIII (endothelium)
Cytokeratin (epithelium)
p53 (may accumulate).
Negative Markers:
Specific infectious agents
Malignancy markers (unless carcinoma)
IBD-associated markers
Autoimmune markers.
Diagnostic Utility:
Highlights vascular changes
Demonstrates fibroblast activation
Excludes malignancy
Usually morphology sufficient
p53 may show radiation-induced changes.
Molecular Subtypes:
Acute radiation injury
Chronic radiation injury
Combined radiation-chemotherapy injury
Dose-dependent patterns.
Molecular/Genetic
Genetic Mutations:
TP53 mutations (radiation-induced)
DNA repair gene defects
Individual radiation sensitivity genes
ATM gene variants
BRCA gene associations.
Molecular Markers:
DNA damage markers (γH2AX)
Apoptosis markers
Inflammatory mediators (TGF-β, TNF-α)
Fibrosis markers (collagen, fibronectin)
Vascular injury markers.
Prognostic Significance:
Radiation dose (most important factor)
Time since treatment
Individual susceptibility
Concurrent therapies
Age at treatment.
Therapeutic Targets:
Supportive care (anti-diarrheal, iron)
Hyperbaric oxygen
Sucralfate enemas
Argon plasma coagulation (bleeding)
Surgical intervention (complications).
Differential Diagnosis
Similar Entities:
Inflammatory bowel disease
Ischemic colitis
Infectious colitis
Drug-induced colitis
Recurrent malignancy
Anastomotic complications.
Distinguishing Features:
Radiation colitis: Atypical fibroblasts, radiation history, field distribution
IBD: Younger age, chronic architectural changes
Ischemic: Watershed areas, acute onset
Infectious: Organisms identified
Malignancy: Dysplastic/malignant cells.
Diagnostic Challenges:
Distinguishing from recurrent malignancy
Recognizing radiation atypia vs dysplasia
Correlating with radiation field
Identifying late effects
Clinical history essential.
Rare Variants:
Acute radiation syndrome
Radiation-induced malignancy
Combined organ injury
Fistula formation
Perforation.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type] from [anatomical location]
Radiation History
Radiation therapy: [yes - dose and dates]. Time since treatment: [duration]
Radiation Changes
Atypical fibroblasts: [present/absent]. Vascular changes: [telangiectasia/sclerosis]. Radiation atypia: [present/absent]
Fibrosis Assessment
Submucosal fibrosis: [mild/moderate/severe]. Smooth muscle changes: [present/absent]
Epithelial Changes
Surface ulceration: [present/absent]. Crypt distortion: [present/absent]. Epithelial atypia: [regenerative/radiation-induced]
Complications
Stricture formation: [present/absent]. Perforation: [present/absent]
Malignancy Assessment
No evidence of dysplasia or malignancy identified
Final Diagnosis
Radiation Colitis - [Acute/Chronic] radiation-induced changes