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Journal of Korean Neurosurgical Society 1975;4(2): 195-206.
A Comparative Histologic Study of Radiogrequency Thermocoagulation and Coagulation in Central Nervous System of Dog.
Tae Sung Park
Department of Neurosurgery, Yonsei University, School of Medicine, Seoul, Korea.
To destroy discrete, circumscribed areas of nervous system in a constant fashion is a prerequisite for a stereotaxic surgery. Many methods including mechanical cutting or Crushing, Chemical Destruction, Cooling, Radiation, and Ultrasound, have been used but each of the above methods has some shortness to fulfill the prerequisite for a stereotaxic surgery completely. In 1960, Saul Aronow devised a radiofrequency lesion generator which could make a discrete and predictive lesion in human nervous tissue. Recently this is widely employed in neurosurgery. Radiofrequency coagulation of tissue satisfying for stereotasic lesions occurs when the current frequencies are between 0.2 MHz and 4 MHz over a wide range of current values1. Most commonly a radiofrequency of 2 MHz is employed. While the dimensions of the lesion are related to the input power, specifically to the obtained temperature, the current, and the duration of current, other specific characteristics such as the geometry of the electrode and the character of the tissue are also operative in determining the final result. In general, the size of the lesion may be more reliably adjusted by changing the electrode than by substituting the other parameters. Within the range of frequencies just mentioned, only a minor portion of the tissue destruction is due to the resistive heating of the electrode and is dependent on the frequency. The major tissue destruction is the result of a dielectric effect depending upon a frequency in the tissues when electric is converted into the heat. The most important factors appear to be the density and the ohmic resistency of the tissue. Cerebral lesions depending upon the heat for their production are influenced by the presence the of blood vessels, the spatial relationship to the cerebrospinal fluid pathways and the tissue resistivity. The greater vascularity of the gray matter and its greater ability to dissipate heat will require more power than is needed to produce a lesion of equal size in the white matter. The histologic examination of the lesions after radiofrequency coagulation in animal central nervous system was reported by Petty and Edsal and Sweet et al. Carpenter and Whittler. inserted magnetic wires into the subcortical structures in the experimental animal. And the head was placed in an electromagnetic field generated by a high-frequency induction heating unit. Resultant lesions were of uniform size and shape with a circular configuration and were unaccompanied by a distant intracerebral injury. Dieckmann studied the histologic changes of the lesions following radiofrequency thermocoagulation in experimental animals. The present study is an attempt to evaluate the histologic changes after radiofrequency thermocoagulation and radiofrequency coagulation in a mammalian cental nervous system, and to compare them. Materials and method; Nine Korean adult dogs weighting an average of 15 kg, were used in this experiment, each being anesthetized with an intravenous injection of Phenobarbital(30 mg/kg), intubated and maintained under the spontaneous respiration. Lesions were produced in the cerebral subcortex by radiofrequency thermocoagulation and coagulation, and were produced in the spinal cord by radiofrequency coagulation utilizing a radiofrequency lesion generator, Radionics Model RFG-3AV. The electrode for thermocoagulation had a 2 mm. Of its terminal bare of insulation. The bare electrode was used for radioquency coagulation. Thermocoagulation was done at from 60degrees C to 80degrees C for two minutes and radiofrequency coagulation of from 50 mA to 110 mA for 15 seconds. The animals were killed at intervals immediately to two weeks. And the lesion to showed histologic changes. The results obtained are summarized as follows: 1. The average size of the lesions in the radiofrequency coagulation group with a 2 mm. Bare electrode was 1.4 by 4.0 mm. at 50 mA, 1.8 by 4.8 mm. at 80 mA and 2.1 y 4.9 mm at 110 mA with equally for 15 seconds. 2. The average size of the lesions in the radiofrequency thermocoagulaton group with a 5 mm. Bare electrode was 5.3 by 7.5 mm. at 60degrees C, 7.5 mm by 9.7 mm at 70degrees C and 8.6 by 11.6 mm at 80degrees C with equally for 2 minutes. 3. Repeated lesions in the same area as that of the primary lesion caused less than 1mm. Increase in size. Thus it was suggested that an operator should make a repeated lesion in human central nervous tissue only after withdrawl or advance of electrode from a primary lesion site. 4. In both groups the majority of lesions had irregular margins. 5. Immediate histologic change of the lesions in both groups were characterized by necrosis, degeneration, hemorrhage and edema;chronic changes by appearance of foam cells in the central area of lesions and granulation tissue in the nearby area. 6. In the spinal cord the histologic changes were more rapid and complete than those in the brain. 7. In both groups the prominent structural changes in mitochondria were disclosed on electron microscopic examination and neuronal changes were progressed greatly within a day in contrasting to the synaptic portion. 8. In the spinal cord the radiofrequency coagulation caused greater destruction of myelin sheath than in the axon. 9. In both groups the size and the margin of the lesions were greatly influenced by spontaneous respiration of the experimental animals.
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