HERPES-SIMPLEX ENCEPHALITIS - LONG-TERM MAGNETIC-RESONANCE-IMAGING AND NEUROPSYCHOLOGICAL PROFILE

The first comprehensive in vivo documentation of the long term profile of pathological and spared tissue is described in a group of 10 patie nts with a diagnosis of herpes simplex encephalitis, who were left wit h memory difficulties as a major residual sequel of their condition. W ith a dedicated MRI protocol, which included high resolution images of temporal robe and limbic system areas, data are provided on structure s that have recently gained importance as anatomical substrates for am nesia. The major features of the lesion profile were: (1) unilateral o r bilateral hippocampal damage never occurred in isolation, and was of ten accompanied by damage to the parahippocampus, the amygdala, specif ic temporal robe gyri, and the temporal poles; (2) the insula was alwa ys abnormal; (3) neocortical temporal lobe damage was usually unilater al or asymmetric. It never occurred in isolation, and was invariably a ssociated with more medial pathological changes; (4) anterior and infe rior temporal robe gyri were damaged more often and more severely than posterior and superior temporal lobe gyri; (5) pronounced abnormality was often present in the substantia innominata (region of the basal f orebrain/anterior perforated substance); (6) there was evidence of sig nificant abnormality in the fornix; (7) there was evidence of damage t o the mammillary bodies; (8) thalamic nuclei were affected in around 5 0% of cases, with damage usually unilateral; (9) frontal lobe damage w as present in a few patients, and affected medial areas more than dors olateral areas; (10) there was some involvement of the striatum, altho ugh this was usually unilateral and mild; (11) there was usually limit ed involvement of the cingulate gyrus and of the parietal and occipita l robes; (12) the cerebellum and brain stem were never damaged. Lesion covariance analysis indicated a close relation between the presence o f abnormalities in temporal lobe and limbic-diencephalic regions. Unli ke severe head injury, lesions in the temporal pole were not associate d with the presence of lesions in the orbitofrontal cortex. Long term neuropsychological impairments were characterised by a dense amnesia i n 60% of cases, and a less severe but noticeable anterograde memory im pairment in the others. Naming and problem solving deficits were found in a small number of cases. Only two patients were able to return to open employment. Severity of amnesia showed a significant relation wit h severity of damage to medial limbic system structures such as the hi ppocampus, with bilateral damage being particularly important. By cont rast, there was a minimal relation between memory loss and severity of damage to the thalamus, to lateral temporal robe areas, or to the fro ntal robes.