Effects at the periphery of the laser lesion in human brain and its tumors after CO2, Nd:YAG, and CO2 high-peak pulsed radiation.

The histological changes in various tissues irradiated with lasers are well known. Our own previous observations with the optical microscope confirm those already reported in the laser literature. If tissue is treated with various laser sources, the results are similar, with the characteristic three layers from the outside toward the inside of carbonization, coagulative necrosis, and edema. Otherwise, only the shapes and sizes of the lesions differ, with craters of different depths. In this paper, we report an ultrastructural study of the changes occurring in the periphery of the laser lesions in both normal human brain and neoplastic tissues (gliomas and meningiomas). Continuous-wave CO2 and Nd:YAG lasers were used at different exposure times and powers and the effects of high-peak pulsed CO2 laser radiation has also been investigated. The study, performed during neurosurgical procedures was mostly focused on microcirculation at 1.5-3 mm outside the area of coagulative necrosis, at the level of the edema zone. Only lesions of the blood brain barrier are produced in normal brain by CO2 radiation (power ranging from 40 to 80 W; exposure time from 3 to 10 seconds). The same results were achieved by Nd:YAG radiation of short duration (3 seconds) regardless of the power used (40 and 80 W). Long-duration Nd:YAG radiation (10 sec; power: 40-80 W) produces endoluminal phenomena leading to the complete occlusion of the capillaries. In neoplastic brain tissues, microcirculation does not seem to be impaired by CO2 radiation. More marked lesions are produced in tumors even after Nd:YAG short-time radiation. Endoluminal obliteration is observed in meningiomas and perivascular hemorrhage occurs in highly vascularized gliomas. According to these results, the risk of delayed post-operative hemorrhages, noticed in some patients with glioblastoma operated on by Nd:YAG lasers, suggests that residual tumor in the cavity should be treated by CO2 laser because of its minimal damage of microcirculation.