Transcortical aphasias may be categorized as either motor or sensory.
- Transcortical motor aphasia (TCMA):
There is a dissociation between preserved repetition (cf. conduction aphasia) and impaired fluency, manifest as delayed initiation, even mutism, impaired lexical selection, and reduced capacity to generate unconstrained syntactic forms. TCMA is associated with pathology (usually infarction) in the supplementary motor area, superior to Broca’s area (left lateral frontal cortex) or in subcortical structures including white matter projections and dorsal caudate nucleus; it has clinical similarities with Broca’s aphasia.
- Transcortical sensory aphasia (TCSA):
There is a dissociation between preserved repetition (cf. conduction aphasia) and impairments of spoken and written language comprehension without phonemic paraphasia. TCSA is associated with pathology (usually infarction) in the ventral and ventrolateral temporal lobe involving the fusiform gyrus and the inferior temporal gyrus, and posterior convexity lesions involving the posterior middle temporal gyrus and the temporo-occipital junction. It has similarities Wernicke’s aphasia.
Some authorities prefer to label these conditions as extrasylvian aphasic syndromes, to distinguish them from the perisylvian aphasic syndromes (Broca, Wernicke, conduction); moreover, these syndromes are not "transcortical" in any literal sense.
Dynamic aphasia (q.v.) may be a lesser version of TCMA, in which there are no paraphasias and minimal anomia, preserved repetition and automatic speech, but reduced spontaneous speech. This may be associated with lesions of dorsolateral prefrontal cortex ("frontal aphasia") in the context of frontal lobe degeneration. There may be incorporational echolalia, when the patient uses the examiner’s question to help form an answer.
Alexander MP. Transcortical motor aphasia: a disorder of language production. In: D’Esposito M (ed.). Neurological foundations of cogni-tive neuroscience. Cambridge: MIT Press, 2003: 165-174
Alexander MP, Hiltbrunner B, Fischer RS. Distributed anatomy of transcortical sensory aphasia. Archives of Neurology 1989; 46: 885-892 Boatman D, Gordon B, Hart J, Selnes O, Miglioretti D, Lenz F. Transcortical sensory aphasia: revisited and revised. Brain 2000; 123: 1634-1642