The histopathological effects of the CO2 versus the KTP laser on the brain and spinal cord: a canine model.

Because no data are available concerning the histopathological effects of the potassium titanyl phosphate (KTP) laser on central nervous tissue, a study was performed using a canine model to compare the histopathological effects of a commonly used laser (CO2) and the KTP laser on brain and spinal cord tissue. Exposed brain and spinal cord tissue were irradiated with 0.1-s pulses (x10), with spot sizes of 1 mm (in focus) over a range of 1 to 10 W. Wedge-shaped lesions were produced with the CO2 laser, while more blunt, semilunar-shaped lesions were produced by the KTP laser. The depth and width of the lesions were proportional to the energy applied. The lesions ranged in surface diameter from 0.6 to 1.3 mm for CO2 and 0.8 to 1.6 mm for KTP lasers, respectively. The depth of the lesions varied from 0.4 to 2.0 mm for CO2 and 0.3 to 1.1 mm for KTP lesions. Histopathologically, a central zone of tissue destruction and vaporization was surrounded by a zone of coagulative necrosis, in turn surrounded peripherally by a zone of pallor. CO2-induced lesions were histologically more hemorrhagic than KTP-induced lesions. In view of the histopathological findings, the KTP laser appears as safe as the CO2 laser in terms of tissue lateral thermal change (penetration) and tissue absorption. The additional hemostatic advantage observed clinically for the KTP laser is demonstrated histologically as well. Although the wavelength of the KTP and argon laser light are similar, the histopathological effects seem to be less pigment dependent. The KTP laser seems well suited for neurosurgery and has the versatility provided by a fiberoptic delivery system.