|A gross photograph of lung demonstrating areas of fibrosis on the pleural surface (arrow). |
Image courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. ; Associate Editor: Cafer Zorkun, M.D., Ph.D. 
Radiation fibrosis defined as the formation of scar tissue as a result of radiation therapy.
The lungs are extremely vascular; thus, the radiation changes seen in the vasculature can have a profound effect on the lungs. During the immediate post-irradiation period, endothelial cell swelling and vacuolization can be seen in the alveolar capillaries. The increased vascular permeability may lead to marked pulmonary congestion and edema and the other changes similar to those encountered in adult respiratory distress syndrome.
Long-term pulmonary consequences of radiation injury include fibrosis of the alveolar walls as well as the vascular changes (vessel narrowing). The respiratory dysfunction due to the combined alveolar wall fibrosis and thickening as well as the poor perfusion due to the vascular lesions can severely inhibit pulmonary function. This radiation pneumonitis creates a profound alveolocapillary block.
Vascular changes, which are dose/rate dependent, are prominent in all irradiated tissues.
Endothelial cells are not specifically radiosensitive but with high exposure vascular changes can occur. There is endothelial swelling and vacuolation or even death of the endothelial cells which can then lead to secondary thrombosis or hemorrhage.
At later time points, intimal hyperplasia and fibrosis occurs which results in thickening of the vessel wall and narrowing of the vessel lumen. These vascular changes can lead to poor blood flow to the tissues.
Radiation can lead to alterations in the mitotic process resulting in cells that have abnormal mitotic figures. These changes can lead to death of the cell. Subtle genetic injuries, such as DNA strand breaks, are responsible for translocations and deletions. These changes lead to the mutagenic, teratogenic, and carcinogenic potentials of ionizing radiation that become evident many years after the radiation exposure. During this long time interval, sequential mitotic divisions are occurring that will ultimately lead to these untoward consequences. This phenomenon is known as radiation "latency."
Radiation Fibrosis in Lungs: A Case Example
A 60-year-old white female had developed retraction of her left nipple six years earlier, at which time breast carcinoma was found. A radical mastectomy was performed.
Examination of the surgical specimens showed metastases in regional lymph nodes and local irradiation was thus administered. Two years later, carcinoma of the right breast was found. Following a modified mastectomy, more irradiation was given. A year later the patient developed recurrences for which chemotherapy (cytoxan and adriamycin) was given.
After a two year period without problems, the patient developed decreased exercise tolerance, dyspnea on exertion, shortness of breath, paroxysmal nocturnal dyspnea, and orthopnea increasing in severity over 10 days.
Chest examination revealed decreased breath sounds with dullness over the left base.
Chest x-ray showed a globose cardiac silhouette and left pleural effusion. A pericardiectomy was done because of suspected cardiac tamponade; however, the patient died soon after the operation.
There was metastatic carcinoma in the pericardium, chest wall, diaphragm, both lungs, and mediastinal lymph nodes. Severe non obstructive cardiomyopathy, probably secondary to adriamycin, was found. Areas of pleural thickening with adhesions and interstitial fibrosis were found involving the anterior aspect of both lungs.
Images courtesy of Professor Peter Anderson DVM PhD and published with permission © PEIR, University of Alabama at Birmingham, Department of Pathology
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