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Biomedical subjects

R P Lesser

Publications and source records attributed to R P Lesser.

At least 73 records · Page 4Linked to original sources
PubMed1988

Localization of cortical function: new information from extraoperative monitoring of patients with epilepsy.

Intraoperative cortical stimulation for evaluation of cortical function has been used extensively to define the extent of cortical excisions for surgical treatment of epilepsy. With chronic implantation of subdural electrodes, extraoperative cortical stimulation becomes possible, and these favorable testing conditions permit more precise mapping of the cortex. This assists the surgeon in planning details of the surgical removal and also provides additional data about the function of the human cortex. Four aspects in which detailed extraoperative studies have provided information complementing the pioneer studies of Foerster, Penfield, and others will be discussed here: (1) Frontal eye field: In the human, this is always an integral part of the motor strip (most probably located in Brodman's area 4 and/or 6) and elicits only conjugate eye movements to the contralateral side with a variable upward component. (2) Negative motor area: Stimulation of the inferior frontal gyrus immediately in front of the face area and of the supplementary motor area of the dominant and nondominant hemisphere produces "inhibition" of voluntary fine movements. (3) The movement related potentials (bereitschaftpotential, negative slope, and motor potential) are strictly localized to the portion of the sensorimotor strip where the movement is represented. Lower amplitude bereitschaftpotentials can also be detected in the homotopic ipsilateral sensorimotor cortex and in the supplementary motor cortex. (4) Three language areas can be distinguished by electrical stimulation: Broca's, Wernicke's, and the basal temporal language area. Electrical stimulation in all these areas produces a similar deficit, but Broca's area tends to overlap with the inferior frontal negative motor area. This may explain the predominant motor deficit of Broca's aphasia.

Brain Mapping↗
PubMed1988

Ictus emeticus: an electroclinical analysis.

We report 31 episodes of ictal vomiting in nine patients, documented by simultaneous video and EEG recordings. In four patients, chronically implanted subdural electrode arrays recorded the event. Only one patient showed "projectile" vomiting. Amnesia for the episode occurred in eight of the nine patients. Interictal epileptiform abnormalities were maximal in the right temporal region in seven patients and bitemporal in two. Ictal epileptiform abnormalities were lateralized to the right hemisphere and involved temporal lobe structures in all patients. Three of four patients recorded with subdural electrode arrays were seizure-free following right temporal lobectomy, and the fourth continues to have ictus emeticus at a reduced rate. The consistent right hemisphere lateralization of seizures in this series corroborates with earlier reports documenting right-sided lateralization in four of five previous cases. Two features that help delineate paroxysmal vomiting as an ictal event are (1) patient unawareness of vomiting and (2) its association with other ictal phenomena.

Adolescent↗
PubMed1987

Electrophysiologic pathologic correlations in patients with complex partial seizures.

We studied interictal activity and site of ictal onset in 26 patients with complex partial seizures of temporal lobe origin. All patients had prolonged electrocorticographic recordings from subdural electrode arrays placed both over the convexity and beneath the temporal lobe. We found a significant correlation between the epileptogenic focus and the type of pathologic lesion found at time of surgery. Macroscopic lesions strongly tended to have an epileptogenic focus on the lateral surface of the temporal lobe; patients with only microscopic abnormalities tended to have an epileptogenic focus in the mesial/basal region of the temporal lobe.

Brain Mapping↗
PubMed1987

Extraoperative cortical functional localization in patients with epilepsy.

Functional localization prior to cortical resections for intractable seizures has usually been performed in the operating room in awake patients. Chronically placed subdural electrodes offer the possibility of performing such testing outside of the operating room and without the unavoidable stresses and time limitations of the surgical setting. The use of the technique is reviewed.

Electrodes, Implanted↗
PubMed1987

The source of 'paradoxical lateralization' of cortical evoked potentials to posterior tibial nerve stimulation.

We report the potentials elicited by posterior tibial nerve stimulation and recorded simultaneously from the scalp and from electrodes within the interhemispheric fissure. The primary cortical potential was recorded from cortex contralateral but from scalp ipsilateral to the stimulated nerve. The scalp recordings thus demonstrated "paradoxical lateralization" as reported previously, and the similar morphology of the scalp and contralateral cortical recordings confirm that this "paradoxical lateralization" is most likely the result of a horizontal dipole located within the interhemispheric fissure.

Adolescent↗
PubMed1987

Clinical outcome after complete or partial cortical resection for intractable epilepsy.

This is the first epilepsy surgery series to analyze the definition of "completeness" of resection, based solely on results of chronic scalp and subdural EEG recording. When patients had complete removal of all cortical areas with ictal and interictal epileptiform discharges, the clinical outcome was usually good. When areas with epileptiform discharges were left behind, good outcome was significantly less frequent. This correlation between complete resection and good outcome was independent of the presence or absence of CT-detected structural lesions or sharp waves on post-resection electrocorticography. These results support completeness of resection, defined by prolonged extraoperative EEG, as an important factor in seizure surgery.

Adolescent↗
PubMed1987

Cortical generators of somatosensory evoked potentials to median nerve stimulation.

In 12 patients with intractable partial seizures, chronically implanted subdural electrodes were used to define the relationship of the epileptogenic focus to cortical functional areas. Cortical somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded from these electrodes. The initial cortical positivity, postrolandic primary cortical potential (PCP), was recorded in all 12 patients with a mean latency of 22.3 +/- 1.6 msec. A potential of opposite polarity, prerolandic PCP, was defined in nine patients with a mean latency of 24.1 +/- 2.7 msec. The latency of the postrolandic PCP was 1.61 +/- 1.59 msec shorter than the prerolandic PCP (p less than 0.01, paired t test). The maximum amplitude postrolandic PCP was 2.1 times larger than the maximum prerolandic PCP (p less than 0.02, paired t test). The phase reversal of the SEPs was compared with the position of the rolandic fissure (RF) defined by electrical stimulation. This study shows that the latency and amplitude characteristics of post- and prerolandic PCPs are significantly different and give support to the concept that they are produced by different generators; and cortical SEPs are helpful in locating the RF.

Adolescent↗
PubMed1987

Electrophysiological monitoring during basilar aneurysm operation.

Intraoperative brain stem auditory evoked potential (BAEP) and somatosensory evoked potential (SEP) monitoring was evaluated in 16 patients each undergoing intracranial operation for basilar artery aneurysm. The 16 patients had 18 posterior circulation aneurysms, including 2 patients with 2 aneurysms. Fourteen aneurysms arose from the rostral basilar artery, 2 arose from the midbasilar artery, 1 arose from the vertebrobasilar junction, and 1 arose from the proximal segment of the posterior cerebral artery. Five aneurysms were classified as giant (i.e., greater than 25 mm), and 5 aneurysms were large (i.e., 15 to 25 mm). Ten patients had BAEP and SEP monitoring, 4 had BAEP monitoring only, and 2 had SEP monitoring only. Two patients showed significant abnormalities during operation, including 1 patient with transient changes in the BAEP when the lower pons and the 8th cranial nerve were retracted. Another patient had progressive increases in latency and decreases in amplitude and subsequent loss of the SEP cortical components during a period of intermittent temporary rostral basilar artery occlusion. Wave P13 was also lost during that period. The cortical components as well as Wave P13 returned after circulation was restored. The BAEPs were unchanged in the same patient during the period of temporary basilar artery occlusion. Fourteen patients had no significant abnormalities. There were no consistent changes during the various stages of operation. BAEP and SEP monitoring failed to identify ischemic events in 4 patients with neurological findings of brain stem ischemia immediately after operation (i.e., 25% false-negative studies).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1986

Magnetic resonance imaging (1.5 tesla) in patients with intractable focal seizures.

Magnetic resonance (MR) (1.5 tesla) studies were performed in ten patients with temporal lobe epilepsy and two with temporofrontal epilepsy. Two patients with temporal lobe epilepsy and one with temporofrontal epilepsy exhibited areas of increased signal intensity on T2-weighted images in the mesiobasal portion of the temporal lobe shown by electroencephalography to be the epileptogenic focus; no analogous abnormalities had been found in these patients on computed tomographic scans. Pathologic studies have not revealed a specific ultrastructural correlate for the MR findings in this group of patients. We found MR to be a useful, noninvasive diagnostic adjunct in the presurgical assessment of some patients with temporal lobe epilepsy. Where abnormalities were found, they corresponded with the epileptogenic focus as defined by electroencephalography.

Adult↗
PubMed1986

Postoperative neurological deficits may occur despite unchanged intraoperative somatosensory evoked potentials.

We describe 6 patients who demonstrated postoperative neurological deficits despite unchanged somatosensory evoked potentials during intraoperative monitoring. Although there is both experimental and clinical evidence that somatosensory evoked potentials are sensitive to some types of intraoperative mishap, the technique should be employed with an awareness of its possible limitations.

Adolescent↗
PubMed1986

Neurophysiological techniques as an aid to surgical treatment of primary brain tumors.

We describe a method of cortical stimulation for localizing functional areas of brain before operation for primary brain tumors that was carried out in 14 patients. The method is unique in that the stimulation is done over several days using chronically indwelling subdural electrode arrays. In addition to cortical stimulation findings, somatosensory evoked potentials were helpful in locating the sensorimotor strip. The neurophysiological data have allowed an aggressive neurosurgical attack without producing a functional deficit.

Adolescent↗
PubMed1986

Cortical potentials related to voluntary and passive finger movements recorded from subdural electrodes in humans.

Movement-related potentials were recorded from subdural electrodes placed on the precentral and postcentral cortex in 3 patients undergoing operation for intractable epilepsy. With self-initiated index finger movement, a negative potential of 25 to 50 microvolts in amplitude, preceding onset of the electromyographic activity by 60 to 95 ms (or onset of movement by 150 to 230 ms), was recorded from the hand somatosensory postrolandic area in all 3 patients. A similar potential preceding the movement was recorded from the precentral hand motor area in one subject who was the only patient in whom the precentral electrodes were placed on the hand motor area. Following active and passive movements, a clearly defined positivity (18 to 32 ms after a photometer trigger) that reversed phase across the central fissure was recorded. The premovement potentials are most probably generated by pyramidal tract neurons and motor-function-related neurons located in the post- and prerolandic areas. The postmovement positivity is most probably due to short-latency kinesthetic reafferent activation of the posterior bank of the central fissure (equivalent to P2 of the somatosensory evoked potentials).

Brain Mapping↗
PubMed1986

The value of closely spaced scalp electrodes in the localization of epileptiform foci: a study of 26 patients with complex partial seizures.

Twenty-seven patients with complex partial seizures were studied electrographically utilizing a large number of closely spaced scalp electrodes around the epileptogenic focus. Skull roentgenograms were made with the electrodes in place in order to relate the electrode positions to underlying brain anatomy. Field distribution maps were constructed from reference montages employing the closely spaced electrode set. Electrodes other than 10-20 were maximal most often and the single electrodes most often maximal were D9-D10, anterior temporal in location. This method of localization is of help in the evaluation of patients with complex partial seizures who may be surgical candidates.

Adolescent↗
PubMed1986

Four dichotic speech tests before and after temporal lobectomy.

Thirty patients were tested with four dichotic speech tests before and after temporal lobectomy for control of intractable seizures. Ipsilateral ear scores improved on all tests postoperatively; these improved scores reached statistical significance for the Staggered Spondaic Word Test and for consonant-vowel syllables. This result, combined with a nonsignificant decrease for contralateral ear scores, produced postoperative increase in the ipsilateral minus contralateral ear difference scores, similar to previous literature. Preoperative tests for a larger group of patients showed significantly poorer performance than for normal subjects, for all four tests. Total correct scores, used as a measure of overall auditory processing capacity, were impaired for these patients, but unchanged or slightly improved after surgery.

Adolescent↗