Intractable temporal lobe epilepsy accounts for approximately 1/4 to 1/3 of all epilepsy, and a significant proportion of these patients have microscopic epileptogenic lesions in the hippocampal tissue, such as microscopic spongiform hemangiomas, low-grade gliomas, and hippocampal sclerosis. These lesions often affect the membrane potential of neurons, causing abnormal bioelectrical activity and epileptiform discharges leading to epileptiform seizures.
In the late 1980s, the combination of stereotactic techniques and computer imaging technology led to the emergence of neurosurgical microsurgical navigation systems. The significance for navigation-assisted resection of small hippocampal lesions is that; it helps the neurosurgeon to set up a three-dimensional surgical plan for the pre-excised surgical range, and intraoperatively, according to the guidance of the navigation wand or navigation microscope, to rapidly reach the temporal horn and confirm structures such as the hippocampus, which can be repeatedly verified by interacting with the preoperative navigation images during resection to ensure effective lesion removal. Since the medial temporal lobe position is relatively deep in fixation, the impact of intraoperative cerebrospinal fluid loss and tissue displacement is less, resulting in fewer navigation errors, while also avoiding damage to important structures surrounded by the medial aspect of the temporal lobe.
As a result, the neuronavigation system allows complete resection of tiny lesions with minimal invasiveness and can effectively avoid optic tract injuries, making the surgery much safer and more reliable.
Since temporal lobe lesions cause gelatinous deformation and cerebral edema in the surrounding brain tissue, structural changes around them, and local abnormalities in material metabolism leading to epileptogenesis, it has been found through research that such epileptogenic foci are mostly located in the area where the lesion is connected to normal brain tissue or in the more external brain tissue, and are often larger than the structural damage itself as seen by appearance and imaging. Preservation of functionally important hippocampal tissue reduces postoperative memory deficits, thus achieving effective epilepsy control.
The early temporal lobectomy and anterior medial temporal lobectomy were performed by intraoperative cortical electrode monitoring and resection of the lesion and surrounding nonfunctional tissues with epileptiform discharges to achieve a more satisfactory surgical result. Therefore, in the late 1950s, Morell proposed to perform multiple submural transverse fiber resections for epileptic foci in functional cortical areas, and achieved certain results.
The main basis is that the human neocortex is horizontally stratified into six layers and arranged by columns that run vertically through the entire cortex, which is the main information transmission structure of the cerebral cortex. Each cortical column contains afferent, efferent and liaison nerve fibers and various nerve cells, which constitute a vertical intra-columnar circuit and can be linked to neighboring cell columns through axons of astrocytes. Afferent impulses enter layer IV, diffuse vertically within the column, and finally impulses from cells in layers V and VI leave the cerebral cortex.
The diffusion pathway of epileptic discharges is dependent on the diffusion of impulses between fibers traveling in the horizontal direction in the superficial cerebral cortex. However, it is not widely used in clinical practice because of the inability to perform subchondral transverse fiber dissection at some sites; the possibility of bleeding; the proliferation of glial cells in the transverse tract and scar formation, which can become new epileptogenic foci; and the difficulty in mastering the depth of the transverse cutter because of the different thickness of the cortex at different sites. In order to solve this problem, domestic scholars have proposed an improvement based on this method, that is, based on cortical EEG monitoring, low power thermal coagulation of superficial cortical transverse fibers is used to cut the cortical level connected fibers for the treatment of intractable epilepsy.
The procedure is simple, without bleeding and scar formation, and preserves the function of the peripheral important cortex while preventing the transmission of epileptiform discharges, resulting in a much higher rate of epilepsy control. Since thermal coagulation of the cortex can only damage the superficial layer of the vertical column structure, the uninjured part still retains its function, so it is important to control the scope and degree of thermal coagulation without affecting the important functions of the cerebral cortex.
Therefore, neuronavigation-guided hippocampal lesion excision combined with superficial transverse cortical fiber low-power thermocoagulation under cortical electrode monitoring is a new method that can be tried in the treatment of intractable medial temporal lobe epilepsy in today’s clinical practice.