Interobserver variation and accuracy in the interpretation of computer tomography in solitary supratentorial brain lesions : Scientific meeting of the Netherlands Society of Neurology, held in Amsterdam, 22nd of April 1989

Abstract

The scalp recorded somatosensory evoked potentials (SSEP) following the stimulation of lower extremity nerve (tibial nerve) consists of P17, P24, P31, N35, N37 and P40. Accumulating evidences suggest that the far-field potentials of P17 and P31 arise from the distal portion of the sacral plexus and brainstem, respectively. These correspond to P9 and P14 of the median nerve SSEPs, respectively. The spinal potential of N23 is equivalent to the N13 cervical potential of the median nerve SSEP. N35 recorded from the ipsilateral hemisphere is analogous to N18 of the median nerve. Paradoxically lateralized P40 is the primary positivity generated at the mesial cortical surface, and it more likely corresponds to P26 of the median nerve SSEP. Thus, the first cortical potential corresponding to N20 is probably a small and inconsistent N37 recorded on the contralateral hemisphere.The somatosensory evoked potentials (SSEP) components of lower extremity nerve stimulation should have comparable components with those of upper extremity nerve SSEP. However, neuroanatomical substrates of lower extremity SSEP has been less well explored and delineated as compared with those of upper extremity SSEP. This is because the recording of lower extremity SSEPs from the scalp or from the spine is technically more difficult and the waveforms are less consistent and more individually variable compared with upper extremity SSEPs. Cervical N13, scalp-recorded P14, N18, and N20 of upper extremity SSEPs are all consistently recordable (obligatory) components, whereas the corresponding potentials of lumbar N23 and scalp P31, N35, and N37, respectively, are not necessarily obligatory components. Recording far-field potentials of P9, P11, P13 and P14 after upper extremity nerve stimulation is relatively easy and can be readily applied to the clinical patients, but recording of the corresponding far-field potentials for lower extremity SSEPs is far more difficult and practically impossible to apply routinely to clinical patients.In this communication, we discuss the neuroanatomical substrate and topographies of lower extremity SSEP comparing with those of upper extremity SSEP.