Partial hemispheric disconnection syndrome of traumatic origin.

A patient presented left-sided apraxia, constructional disturbances with the right hand and left tactile anomia after a severe head injury. MRI showed a callosal lesion involving the middle and posterior third of the truncus. This finding supports the thesis that the posterior callosum plays a predominant role in the interhemispheric mediation for praxis, as well as in the right-left transfer of spatial information guiding constructional performance. Left-sided apraxia was evident on imitation, on verbal command and on visual presentation of an object, but not on tactual presentation and during the actual use of objects. Moreover, apraxia on imitation showed a more rapid recovery than apraxia on verbal command. These data are consistent with the hypothesis of a left-hemisphere dominance for praxis, which is almost absolute when the retrieval of the appropriate gesture requires a semantic analysis of the stimulus.