The Chronological Development of Late Radiation Injury in the Liver of the Rat

Surgically exteriorized left anterior liver lobes of rats were X-irradiated with 8 kR, and changes in liver weight and histology were evaluated for 40 weeks after irradiation. Irradiation prevented growth in the irradiated lobe. A decrease in irradiated lobe weight occurred approximately 14 weeks after irradiation and was associated with parenchymal cell loss. Inflammatory cell infiltration into the irradiated lobe occurred immediately after irradiation and remained constant for 12 weeks after which there was a further increase in numbers of inflammatory cells. Fibrosis was apparent by 2 weeks and exhibited a second increase in severity after 12 weeks. Nuclear injury in some parenchymal cells was apparent in the irradiated lobe, especially after 24 weeks. Concentric lamellations in the veins with compromise of their lumen became evident after the 10th week. The temporal response of these alterations and consideration of other reports on late radiation effects suggest that early liver injury (0 to 12 weeks) is associated with an autoimmune reaction while the more extensive liver injury which occurs later (16 to 40 weeks) is the result of more direct radiation damage to the vasculature.