An Experimental Study Of Spinal Cord Injury Made By Microwave Hyperthermia In Rabbits

Background:The operative therapia of spinal tumor is difficult because of the complicated anatomy in the spine.Recently we try to treat the spinal tumor by microwave hyperthermia,and we obtain the satisfactory result in initial observation.However,the safety of microwave technique and especially the risk of the spinal cord thermal injury must be evaluated before it is widespreadly used in the clinic.Objective:To investigate the effort of hyperthermia on the corresponding spinal cord segment,histopathological changes and the highest tolerable quantity of heat for normal spinal cord function,we establish animal model whose vertebral body heated by microwave.We can offer experimental evidence for the feasibility and safety of the use of microwave technique in the spinal tumor.Methods:1.Six fresh specimens of the vertebrae(L1) in rabbits(age 4months) were used to detect the anatomy characteristic of each vertebrae at the transverse plane of the transverse process root,including the max sagittal diameter of vertebral body,the max transverse diameter of vertebral body,distance between pedicle root point and point of centricity which is the intersection point of the max sagittal vertebral diameter and the max transverse vertebral diameter,angle between the line of central point and pedicle root point and the max sagittal vertebral diameter.2.Thirty Zelanian rabbits were divided into 5 groups at random, and 6 Zelanian rabbits were in a group.Group A was the control,which underwent L1 laminectomy and the spinal cord was exposed without heating vertebral body.Groups B,C,D,E were experimental groups,which underwent L1 laminectomy,the spinal cord and the right face of the vertebral body was exposed. The temperature in vertebral canal of which were 43℃,44℃,45 and 46℃respectively,and all the temperature was kept 30 minutes.The cortical somatosensory evoked potentials(CSEP) was administered at preoperative,instant after laminectomy and 30 minutes after laminectomy in group A.The cortical somatosensory evoked potentials(CSEP) was administered at preoperative,instant after laminectomy and after heating in groups B,C,D,E.The animals were executed 6 hours after operation.The histological changes of spinal cord at the level of L1 was observed after HE and Nissl staining,and specimens of spinal cord were observed by electronmicroscope.Results:1.At the transverse plane of the transverse process root,the max sagittal diameter of vertebral body is 0.600±0.070cm,and the max transverse diameter of vertebral body is 0.980±0.081cm.The distance between pedicle root point and point of centricity is 0.508 cm±0.071cm.The angle between the line of central point and pedicle root point and the max sagittal vertebral diameter is 47.167°±5.115°.The insert point of microwave antenna is the pedical root at the transverse plane of the transverse process root.The angel between microwave antenna and sagittal plane is 45°.And the angel between microwave antenna and transverse plane is zero.The depth is about 0.5 cm.2.There was no statistic significant difference of latency and amplitude of CSEP at different time in the control group,which was at preoperative,instant after laminectomy and 30 minutes after laminectomy.The motor function and sensory function of hind limb were normal at preoperative and postoperative.Neuron and nerve fiber were normal in histopathology.There was no statistic significant difference of latency and amplitude of CSEP between preoperative and instant after laminectomy in the test groups.B group:There was no change of CSEP such as prolonged latency and decreased amplitude after microwave hyperthermia.The motor function and sensory function of hind limb were normal at preoperative and postoperative. Neuron and nerve fiber were normal in histopathology.Group C:There was no change of CSEP such as prolonged latency and decreased amplitude after microwave hyperthermia.The motor function and sensory function of hind limb were normal at preoperative and postoperative.Neuron and nerve fiber were normal in histopathology.Group D:There were some changes of CSEP such as prolonged latency and decreased amplitude after microwave hyperthermia. Muscle strength and sensation decrease after operation.The white matter was in light edema,and the broken nerve fiber and small lesion could be observed occasionally.The quantity of the nerve cells in the gray matter become small. Swelling neurons,shrinking nucleus and point hemorrhage could be observed. The above changes were observed in HE staining.The quantity of neurons stained by nissl staining became small,and nissl's body dissolve.The normal neurons could be observed in nissl staining.The rough endoplasmic reticulum was in derangement.The shrinking nucleus and loose nerve fiber could be observed by electron microscope.Group E:The waveform of CSEP is not endued after microwave hyperthermia.Muscle strength became zero,and sensation disappear after operation.The spinal cord was seriously injury.The big area hemorrhage and broken nerve fiber could be observed in white matter.The quantity of the nerve cells in the gray matter become obviously small.Karyolysis,necrosis and big area hemorrhage could be observed in the gray matter.The above changes were observed in HE staining.The quantity of neurons stained by nissl staining became obviously small and nissl's body disappear.The necrosis could be observed in nissl staining.Karyolysis and broken nerve fiber were observed by electron microscope.Conclusions:1.Heating the vertebral body with microwave and keeping the temperature of the epidural space half hour.44℃in the epidural space is the highest tolerable temperature of rabbits for normal spinal cord function.It is 45℃in the epidural space and keeping the temperature half hour that making the spinal cord incomplete injury.When it exceed the highest tolerable quantity of heat,the more the quantity of heat,the more serious the spinal cord injury.2.It is feasible to make animal model whose spinal cord was thermal injury with microwave antenna.3.It is reliable to monitor spinal cord function by CSEP,and the change of CSEP is correlated with the degree of spinal cord injury.We can roughly judge the degree of spinal cord injury.The CSEP amplitude is more sensitive than latency in judging spinal cord injury.