VERTICAL DISPLACEMENT OF STEREOTAXIC TARGET IN THE CAT BRAIN AFTER BURR HOLE PRODUCTION OF THE SKULL

In order to observe the postoperative vertical displacement caused by various open functional stereotaxic procedures in the coordinate of br ain target, we produced a similar surgical procedure in 14 cats. On pr eoperative computed tomography (CT) scans, certain well defined brain structures (the cortical surface of the brain and the floor of the thi rd ventricle) were chosen as anatomical landmarks and their relationsh ip to the skull were determined with the cat in a prone position. Ther eafter, a burr hole was opened on the right side of the skull of each animal and a small dural incision was made. All animals were re-examin ed with CT scanning using the same technique and the distances to the skull were determined. There was a cortical descent in postoperative c oronal CT images (range 1.2-3.6, mean 2.1 mm). On the other hand, the vertical coordinate of the floor of the third ventricle was found to b e lower than it had been preoperatively, with an average of 0.6 mm low er (range -1.2 -+ 0.3 mm). These results indicate that there was a goo d correlation between the degree of cortical descent and displacement of the vertical coordinate of the floor of the third ventricle (r = 0. 70 and r = 0.69, respectively; P < 0.01). Our results also suggest tha t thalamic targets can be calculated by compensatory adjustment of the vertical coordinate by an additional distance of about half of the ve rtical descent. However, further experimental and clinical studies wil l be needed to determine the validity of this result in human beings.