Modification of neuromagnetic cortical signals by thalamic infarctions.

Auditory evoked responses and spontaneous cortical activity were recorded with a whole-scalp 122-channel neuromagnetometer from 7 patients, who had small thalamic infarctions in the region of the left anterior tuberothalamic artery and associated memory defects. In contrast to healthy control subjects, with dominant rhythmic activity at 10.6 +/- 0.6 Hz in the parieto-occipital region, the spectral maximum in the patients was at 8.9 +/- 0.4 Hz. Abnormal acceleration of rhythmic activity was also observed bilaterally in rolandic areas. Our findings imply that lesions of non-specific thalamic nuclei may disturb human brain rhythms in widespread cortical areas. 'Mismatch responses' to deviant tones (1.1 kHz) among standards (1.0 kHz), suggested to reflect sensory auditory memory in healthy subjects, were absent in 2 patients, markedly decreased in 3, and normal in 2, implying that pathways passing through the anteromedial thalamus contribute to modulation of these responses. We conclude that local unilateral lesions in the anteromedial thalamus may cause extensive, bilateral alterations in the brain's electric activity.

Spin-echo MRI of chronic intracerebral haematomas.

Our purpose was to characterise the MRI appearances of clinically non-neoplastic chronic intracerebral haematomas (ICH). We examined 25 patients with a history of clinically non-neoplastic 0.5-to 1.5-year-old ICH who underwent prospective follow-up 1.0-T spin-echo MRI of the brain. On T1-weighted images most lesions gave lower signal than white matter and were isointense with cerebrospinal fluid (CSF). On T2-weighted images most were either totally low-signal and slit-like, or had a high-signal centre and a low-signal margin. The low-signal (haemosiderin) rim showed areas of discontinuity in 7 cases. Of 24 lesions, 4 showed small enhancing areas on contrast-enhanced images. In 10 cases the brain parenchyma surrounding the lesion showed high-signal on T2- and low signal on T1-weighted images, probably representing encephalomalacia. In 20 cases enlargement of a nearby CSF space was observed, and 14 cases showed atrophy of the brain stem ipsilateral to the lesion. We thus found more variation on MRI of clinically non-neoplastic chronic ICH than previously described.