Value of full-field visual evoked potentials for retrochiasmal lesions.

Some abnormalities in the P100 on monocular stimulation have been said to indicate retrochiasmal abnormalities. This study was undertaken to evaluate the reliability of visual evoked potentials (VEPs) for this purpose. We retrospectively reviewed VEPs that could be interpreted as indicative of a retrochiasmal lesion, based on an amplitude asymmetry of >50% between the P100 recorded on the left and right occipital regions. The abnormality had to be present on both left and right monocular stimulation (uncrossed pattern). Studies were conducted in accordance with the guidelines of the American Electroencephalographic Society. Findings on magnetic resonance (MR) imaging were analyzed. For comparison, we also studied a control group of 30 patients with normal VEPs. During a 16-month period, we identified 15 patients who fulfilled the aforementioned criteria and who had undergone an MR scan of the brain. Eight scans were normal and seven were abnormal. Of the seven abnormal scans, five revealed multiple periventricular white matter lesions in both hemispheres suggestive of multiple sclerosis: one a single punctate white matter lesion in the left frontal corona radiata, and one multiple white matter lesions in the basal ganglia, brainstem, and cerebellum but not in the hemispheres. In the control group with normal VEPs, nine had at least one hemispheric lesion on MR scans. This yielded a positive predictive value of 33%. The negative predictive value was 70%, sensitivity 36%, and specificity 68%. Because of a high rate of false positives, full-field VEPs were not reliable in predicting retrochiasmal lesions.

Brain-stem auditory evoked potentials (BAEPs) from basal surface of temporal lobe recorded from chronic subdural electrodes.

BAEPs were recorded from the basal surface of the temporal lobe by subdural electrodes chronically implanted in 6 patients who were evaluated for surgical management of intractable partial seizures. Near-field recordings were obtained by recording between the subdural electrode closest and most distant to the brain-stem. Far-field recordings were obtained by recording between the subdural electrodes and an indifferent electrode over the spinal process of the seventh cervical vertebrae. The recordings were compared with standard ear-vertex recordings. After ipsilateral ear stimulation, the subdural electrode closest to the brain-stem recorded large amplitude waves I and II followed by less well-defined waves of longer latencies. Recordings to contralateral stimulation showed no clearly defined waves I and II and a large amplitude wave Vn. Waves III, IV, V, Vn and VI were of opposite polarity after ipsi- and contralateral stimulation. These findings indicate that waves I and II are generated ipsilaterally to the stimulation side, whereas wave Vn has a contralateral origin. Wave Vn may be generated in the brachium of the inferior colliculus, as suggested from dipole configuration studies. This conclusion is consistent with the classical anatomical observations that the supracollicular auditory pathways are predominantly crossed.

Posterior fossa intraoperative monitoring.

Monitoring of brainstem structures is requested of the neurophysiologist for both intra-axial and extra-axial surgeries of the posterior fossa. A variety of techniques to include upper extremities somatosensory evoked potentials, short latency auditory evoked potentials, spontaneous and evoked electromyographic activity, and recordings from the cochlea and the eighth nerve are available. The indication, implementation, and interpretation of each of these modalities are delineated. The efficacy and utility of these techniques are also discussed.

Hemorrhagic cardioembolic stroke: is anticoagulation absolutely contraindicated?

Hemorrhagic cerebral embolism should not be considered an absolute contraindication to immediate low-dose systemic anticoagulation. Low levels of anticoagulation may give some protection from recurrent embolism while minimizing the risks of intracranial bleeding. Until further studies are available, these decisions must be made on a case-by-case basis, supported by limited scientific information.

Transient appearance of periodic EEG discharges in senile dementia.

We describe an elderly patient with probable Alzheimer's disease whose EEG and clinical status improved rapidly coincident with normalization of temperature. This finding suggests that her transient illness, of fever, pneumonia and confusional state, triggered the production of this periodic EEG pattern. With the increased prevalence of dementia in our aging population, we predict that the appearance of a multifocal periodic triphasic sharp wave pattern in the EEG of chronically demented patients (with superimposed infection) will become more common. Only when this pattern persists over time and the patient is not systemically ill, is this pattern a reliable discriminator for CJD. Serial EEGs in this setting (after treatment of the systemic illness) might reveal the transient nature of the periodic EEG change, thus avoiding the erroneous conclusion that the patient's dementia is a manifestation of CJD.

Extensive brain calcification and progressive dysarthria and dysphagia associated with chronic hypoparathyroidism.

An 81-year-old woman with a 13-year history of hypoparathyroidism developed dysarthria and dysphagia. Cranial computed tomography demonstrated extensive calcification involving the basal ganglia, corona radiata, and deep cerebellar structures. The cerebral small-vessel calcification that occurs in chronic hypoparathyroidism may produce the syndrome of progressive dysarthria and dysphagia.