Abstracts

Spinal cord intra-operative neuromonitoring has become an important tool in the armamentarium of clinical neurophysiologists helping surgeons improve the outcome of patients. We have been using standard techniques of spinal cord monitoring to evaluate the integrity of different pathways during spinal surgeries.
In this study, we introduce our experience with a newly reported technique which we have implied and started using as an addition to our monitoring tools. This technique consists of direct stimulation of the dorsal columns and recording antidromic potentials from the peripheral nerves in four extremities in order to localize the median raphe. This procedure is called [ldquo]dorsal column mapping[rdquo] and is used by surgeons for better identification of the median raphe hoping to minimize injury during myelotomies in cases of removal of intramedullary tumors, syrinx etc. We stimulate the dorsal columns by a concentric bipolar stimulator at 2mA. We record from the bilateral ulnar nerves at the wrist and from the bilateral tibial nerves at the popliteal fossi. We average the signals till it is well defined and report to the surgeon weather the potential is recorded at all and if it is right, left or bilateral. We expect to see a right sided potential stimulating the right dorsal column, a left sided potential stimulating the left dorsal column, and no response or bilateral equal response when the median raphe is stimulated. Twenty one mapped cases are compared to twelve non mapped cases in terms of SSEP deterioration after myelotomy and recovery. We have been collecting cases of dorsal column mapping done during myelotomies for intramedullary tumor resection or syrinx drainage. So far we have twenty one cases mapped.
SSEPs severely deteriorate after myelotomy in 50% of non mapped cases compared to 28% in the mapped group. SSEPs do not change at all or improve in 16% of non mapped cases compared to 52% in the mapped group.
The impression of the surgeons as reported by them and ours is that this technique is very useful in identifying the median raphe, taking in consideration the changes of normal anatomy due to the underlying pathology which makes the identification very difficult for the surgeon. Once the identification is better, the likelihood of injury to the dorsal columns is reduced. This new technique, as well as other previously mentioned techniques are robust and sensitive for identifying injury of the spinal cord. By better identification of the median raphe we can obtain reduced likelihood of injuring the spinal cord.
The best results we see are in patients undergoing their first myelotomy as compared to multiple myelotomies and scarring, where the mapping is less robust.
we are conducting more sophisticated statistical analysis comparing outcome by region and pathology.