[Regression of Yoshida sarcoma during normoxia and hypoxia after fractionated irradiation]

Vascularization of the area between free grafts and irradiated graft beds in the neck in rats

Inflammatory lesions of the vascular endothelium after preoperative radiotherapy often cause healing-delayed healing of free flaps in the irradiated graft bed. We investigated changes in neovascularization in the transition area between grafted tissues and irradiated tissues of the graft bed. We irradiated the neck(30 and 50 Gy total dose) in 102 Wistar rats and then grafted a free myocutaneous gracilis flap to the irradiated region of the neck 4 weeks later. We examined histologically the tissues of the graft, the transition area between the graft and the irradiated graft bed, and the graft bed. In contrast to control rats, the tissues in the irradiated animals showed a qualitatively reduced and a more irregular capillary distribution, with substantial fibrosis in the irradiated graft bed. We also found significant differences in vascularization and mean capillary lumen in the transitional zone between graft and graft bed in the irradiated rats compared with controls (P = 0.004 and P < 0.001, respectively). Both number and diameter of capillaries were reduced in the irradiated graft bed tissue. The graft failed to improve vascularization in the transitional zone between graft and irradiated tissue, so we conclude that it is the vascularization status of the bed tissue rather than that of the transplant tissue that is the limiting factor for graft healing.