Stereotactic CT scan and its correlation with the neural activity of deep structures

An attempt has been made to visualize beforehand a brain section through which an electrode would pass to reach the target point in stereotactic thalamotomy for the treatment of tremor. On the basis of several craniometric measurements of a plain craniogram (lateral view), the level of the intercommissural line could be approximately estimated and a tentative target point set on the craniogram. Then, a line is drawn to connect this target point and the bregma. Extrapolating this line, an angle between the Reid baseline and this line could be measured in order to transfer the line to the scalp. With the aid of a GE scanner (GE-CT/T-X2), several 5-mm thick sections are made parallel to this line including the tentative target point. Among these images of CT scan thus made, referring to the foramen of Monro and the aqueduct (either of which might be visualized) one of the sections would be chosen as a tentative plane through which the electrode would pass. On the operation day, a burr hole should be made on or near the line used for CT scanning and drawn on the scalp, so the electrode tract will coincide with the CT scan image. GE scan images are clear enough to estimate the range of gray matter, white matter, caudate nucleus and thalamus. The neural activities of the deep structures recorded during the operation by stepping displacement of the electrode are correlated with this CT scan image. So far, the coincidence of both findings are satisfactory and of great value in this kind of blind operation.