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into the internal capsule, if the lesion is placed too inferior then there will be ataxia of the hand during finger to nose testing. Thus by clinical testing alone during infliction of the ventrolateral thalamic reversible lesion, the surgeon may delineate the posterior, lateral and inferior boundaries (8).
Before this procedure was popularized Narabayashi and Okuma performed chemical pallidotomy of the anterodorsal pallidum, which resulted in relief of rigidity but not tremor and hypokinesia. Leksell ablated the posteroventral pallidum with long lasting relief of tremor, rigidity and bradykinesia. Laitinen (17) reported the previous results as well as their more recent experience with 38 Parkinson's patients who failed or were not candidates for extensive conservative therapy. Their target was based upon CT imaging and lay 2 to 3 mm in front of the midcommissural point and 20 to 22 mm lateral to the midline of the third ventricle. The final lesion was based upon the patient's reaction to initial temporary lesioning. Final lesions were 6 to 7 mm in the dorsoventral length and 6 mm in transverse length, which placed the lesion just lateral and dorsal to the nearby optic tract, medial to the internal capsule and just dorsal to the amygdala. By 1970 more than 5000 individuals underwent cryolesioning with a mortality of 1.2% and a hemorrhage incidence of 0.8% (27). Both of the procedures remained popular until the introduction of the Dopamine agonist for the treatment of Parkinsonism, which yielded the equivalent results without the surgical destruction. At the present time the thalamotomies are reserved for those individuals who failed medical therapy. Additional procedures are available including the insertion of brain stimulating electrodes and possible tissue transplantation.
GLIOBLASTOMAS AND OTHER TUMORS
There are many advantages of using cryosurgery in the treatment of selected tumors as previously stated under advantages and disadvantages. The lesions can be placed through a burr hole, create hemostasis and can necrose deeply situated otherwise, inoperable neoplasms of the brain. The cryogenic cannula can also be placed into the center of a tumor, freezing it and thus causing shrinkage, avascularity, hypothermia of the surrounding brain and separation, allowing it to be dissected relatively easily en bloc. Walder (30) who previously criticized Cooper, stated that cryosurgery yielded increased survival time when compared to conventional surgery because not only was the lesion completely macroscopically removed, the surrounding tissue was cold cauterized and there was no apparent spillage of tumor tissue. Although gross total resection of glioblastoma (GBM) does increase survival when compared to biopsy alone (1), no more than 15% of gliomas are able to be completely removed (24). If standard therapy fails, there are only a limited number of options, which include reoperation. Albeit an increased survival rate with (Continued on page 86)
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