Intraoperative median nerve somatosensory evoked potentials (SEP) were monitored in 28 patients undergoing surgery for cervical or cervicothoracic syringomyelia. Analysis was focused on SEP components N13 (spinal cord), P14 (brain stem), and N20 (cortex). N13 was lacking in nearly 87% of the patients (due to a combined effect of syringomyelia and general anesthesia) and never recovered. P14 showed a significant (> 10%) intraoperative latency increase in two patients; this was irreversible in one patient who had a postoperative worsening of sensory function. N20 showed no relevant alterations. Pure motor deficits after surgery were not predicted by SEP monitoring. In conclusion, intraoperative P14 recording helped to identify harm to the dorsal columns and probably prevented the cord from irreversible damage in one case, whereas N13 recording did not contribute to the monitoring of spinal cord function during surgery for syringomyelia.
The question is posed whether in the investigation of intracranial tumors, particularly in the posterior cranial fossa, CT and/or ventriculography should be practiced. We investigated 134 patients (93 were children up to the age of 14 years), all of whom had had both computed tomography and ventriculography. The results clearly demonstrate the superiority of CT compared with ventriculography. Ventriculography is a surgical intervention with risk for the patient; side effects may occur and serious complications can sometimes arise. Modern CT is producing pictures of high quality which are entirely sufficient for neurosurgical intervention. Very rarely does additional angiography have to be performed. The diagnosis of intracranial tumor can be fully established by CT and ventriculography is no longer necessary.
Median nerve somatosensory evoked potentials (SEPs) were recorded in 30 patients with cervical syringomyelia before and after surgery. The different SEP components were compared with clinical somatosensory findings. The N13 potential (generated in the dorsal horn at C5-C6) was pathological in 85% of the upper extremities, or 90% of the patients, and correlated with pain/temperature as well as vibration/joint position sense; it was of higher sensitivity in syringomyelia than any other clinical symptom or SEP component. P14 (brain stem) and N20 (postcentral cortex) were less often affected and correlated with only vibration/joint position sense. Short-term postoperative clinical or SEP changes were most often seen after syringoendoscopy and less often after syringostomy, resection of cerebellar tonsils, or tumor extirpation. Alterations of SEPs after surgery occurred in more patients (60%) than did changes in clinical condition (approximately 27%); there was, however, no general correlation between these findings. We conclude that median nerve SEP testing with a proper recording technique identifying the different subcortical components is a valuable supplement in the pre- and postoperative diagnostic evaluation of syringomyelia and is of higher sensitivity than clinical somatosensory examination alone.
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