The locus and extent of the lesions in the the brain for 124 cases with various types of aphasia due to cerebrovascular accident were examined by the computerized axial tomography. The relationship between the loci of the lesions and the diagnostic types of aphasia was investigated with the following results:
1. A figure of the lateral view of the brain illustrating the lesion site was made from the horizontal tomogram for each patient. Figures thus obtained for all the patients in each diagnostic type of aphasia were superimposed on each other with the following findings.
a) The accumulated site of aphasia-producing lesions for the entire group of aphasic patientsextended to the whole area of the brain supplied by the left medial cerebral artery.
b) The highest frequency of the involvement was observed at the lower part of the pre-Rolandic gyrus.
c) The patients with simple aphasia (amnestic aphasia) showed no consistent locus of the lesion.
d) The patients with “nonfluent” or “motor” type of aphasia (i.e., aphasia with sensorimotor impairment and aphasia with persistent dysfluency), as well as the patients with “pure” apraxia of speech, showed a highly frequent involvement at the postero-inferior part of the frontal lobe, i.e., Broca's area.
e) The patients with “sensory” type of aphasia (i. e., aphasia with intermittent auditory imperception), showed a highly frequent involvement at the upper part of the temporal lobe, i.e., Wernicke's area.
f) The patients with global phasia showed an extensive involvement of the brain with no specific lesion site.
g) The patients with conduction aphasia showed the involvement highly limited to the supramarginal gyrus of the brain.
2. Differential diagnosis of aphasia using the statistical technique based upon the data for the lesion site showed a hit rate of 62%. The majority of the non-hit cases were those with simple aphasia characterized by a poor lesion-site/diagnostic type correspondence. For the rest of the patients with other diagnostic types of aphasia, the rate of correspondence between the lesion site and the diagnostic type was highly reliable.
