PubMed · 5311529
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T H Milhorat. 1970-10-01. Cerebrospinal-fluid dynamics.. https://pubmed.ncbi.nlm.nih.gov/5311529/
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The techniques of targeting the subthalamic nucleus (STN) and the ventralis intermedius nucleus (Vim) are similar, only the coordinates are different. Targeting ideally consists of gathering all data about a target and positioning the electrode correctly within that target. The electrode should be positioned within a statistical range of coordinates, where the neuronal firing fits a given pattern and responds to external stimuli, particularly to proprioceptive inputs, in a somatotopically organized manner. Moreover, final placement should provide the best clinical improvement of symptoms under the stimulation parameters expected to be used in the long term. This latter criterion is by far the most important, because intraoperative findings indicate the functional benefit for the patient, which is the ultimate purpose of this surgery. A variety of radiological modalities are available to provide data for electrode placement, but each type has its drawbacks. Ventriculography, although safe when performed accordingly to strict technical procedure, is the most precise method but provides more indirect targeting and is more invasive than magnetic resonance imaging (MRI). MRI is the best method for visualizing the STN and, to some extent, for discerning the Vim, but it is plagued with unpredictable and nonreproducible deformations that induce a systematic distortion. These shortcomings no doubt will be corrected in the near future, and the technologies will better assist us in the proper placement of electrodes, which will provide the patient with the highest possible benefit.
We evaluated the direct location in the globus pallidus (GP) under stereotactic MRI (sMRI) guidance in five parkinsonians treated with chronic deep brain stimulation (four bilaterally). The sMRI consisted of three orthogonal (horizontal, frontal, sagittal) sets of images obtained with a stereotactic frame and its localiser. The sMRI was coupled with ventriculography to compare the location with the classic indirect method based on commissural landmarks. The target was defined on T2-weighted slices in the anterior part of the medial GP, at the vertex of the nucleus. It was reached via one track with a semi-micro-electrode and step by step high frequency stimulation, then replaced by a quadripolar electrode once we located the site enabling the optimal clinical improvement. Stereotactic x-rays localised the final position of the electrode. A company software matched sMRI, ventriculography, and peroperative (perop) x-rays, with reference to the stereotactic location boxes. We analysed the effects of acute (perop) and chronic (six-month follow-up) stimulation of active plots (acplots), i.e. leading to optimal clinical improvement. Three distances with reference to the acplots were measured both on sMRI and ventriculography: the laterality from the median sagittal plane of the third ventricle; the anterior position from the midpoint of the intercommissural line (Icl), and the vertical position with regard to the Icl. We then compared the differences in measurements (n = 64) with the Bland and Altman method. The mean difference was 0.09 mm with 95% of the values between +/- 1 mm, but only the laterality had a statistically significant agreement (all the differences included between +/- two times the standard deviation of the mean). The acplots distances from the dorsal, ventral, and medial boundaries of GP (defined by manual surrounding on frontal and horizontal planes) were measured on sMRI. With one exception, the acplots were all included in the nucleus. The six-month acplots were located dorsally with reference to the perop ones. Clinical benefit at six-months follow-up showed results comparable to the literature. Direct location of GP target based on sMRI seems a simple and reliable method.
A patient who had undergone ventriculoperitoneal shunting developed upper cervical myelopathy. His CSF pressure was markedly low, and deformation of the spinal cord and shrinkage of the subarachnoid space at the upper cervical level were found in radiologic examinations. Ligation of the shunt tube resulted in almost complete recovery. The effect of excessive drainage may have caused the abnormalities.