[Somatosensory evoked potentials in intraspinal tumors]

SEPs have been recorded in 15 patients with spinal cord tumors (mostly ependymomas) and in 5 patients with cord compression due to meningiomas (3 cas), neuromas (1 case) or neurosarcoma (1 cas). All the patients have been operated on so that precise informations were available on the histology and the location of the tumor. SEPs were monitored during surgery in 8 patients. The main conclusions of this study are as follows: There was a good correlation between the somatosensory troubles for touch, vibration sense and joint position sense, and SEPs abnormalities, however, SEPs may be clearly abnormal in the absence of any somatosensory deficit when the dorsal columns are compressed and not infiltrated by the tumor. In the latter situation the reverse dissociation (i.e., normal SEPs with somatosensory troubles) may be observed. The possibility of a dissociation between normal N11 and N13 cervical components and absent P14 far field components (non-cephalic reference) has been confirmed in 6 patients with cervicomedullary tumors. In 3 of them, this dissociation was found to be reversible and early SEPs returned to normal after surgery. Peroperative monitoring of scalp SEPs recorded with a non-cephalic reference electrode allowed the detection of transient SEP abnormalities related with a traction on the dorsal columns of the cord. SEP monitoring is recommended for any surgical removal of tumor that needs a posterior myelotomy.