The human pyramidal syndrome Redux.

Experimental studies in nonhuman primates have questioned the selectivity of pyramidal tract damage in giving rise to the classical pyramidal syndrome in humans, characterized by permanent spastic hemiplegia (PSH). According to this view, concomitant injury of extrapyramidal pathways is necessary for the development of both hemiplegia and spasticity. In this study we used conventional magnetic resonance imaging and diffusion tensor imaging tractography to characterize the anatomical correlates of PSH in a patient with a rare and discrete unilateral lesion of the medullary pyramid. Our findings support the hypothesis that damage confined to the medullary pyramid/pyramidal tract is sufficient to produce PSH. In contrast to nonhuman primates, the human 'pyramidal' and 'pyramid' syndromes are equivalent clinico-anatomic concepts.