Aphasia and Cortical Lesion Syndromes
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Direct answer
Aphasia is an acquired language disorder from dominant hemisphere damage, localised by three questions: is speech fluent, is comprehension preserved, is repetition intact. Broca aphasia is non-fluent with preserved comprehension, reflecting an inferior frontal lesion, while Wernicke aphasia is fluent with impaired comprehension, reflecting a posterior superior temporal lesion. Conduction aphasia is fluent with good comprehension but disproportionately poor repetition, from damage to the arcuate fasciculus or adjacent perisylvian cortex.
What you must remember
- Broca aphasia: non-fluent, effortful, telegraphic speech with preserved comprehension and poor repetition, often with right facial and arm weakness from a frontal lesion.
- Wernicke aphasia: fluent, paraphasic speech with neologisms, poor comprehension and poor repetition; hemiparesis is usually absent, but a superior quadrantanopia can accompany it.
- Conduction aphasia: fluent speech and good comprehension, with repetition impaired out of proportion and phonemic paraphasias; patients often recognise and correct their own errors.
- Global aphasia: non-fluent with poor comprehension from a large perisylvian lesion in the middle cerebral artery territory.
- Anomic aphasia: word-finding difficulty with fluent speech and intact repetition, a nonspecific sign of temporal or angular lesions.
- Lobar signs: frontal lesions cause abulia and gait apraxia, parietal lesions cause neglect and anosognosia, temporal lesions cause a contralateral superior quadrantanopia, and occipital lesions cause homonymous hemianopia with macular sparing.
- Gerstmann syndrome: finger agnosia, left-right disorientation, dysgraphia and acalculia from a dominant angular gyrus lesion.
A worked case: fluent nonsense after a stroke
A right-handed 60-year-old man is found after a stroke speaking fluently but producing nonsensical words, and he does not follow simple commands.
- Apply the three questions: Speech is fluent, comprehension is poor and repetition fails, so the picture is Wernicke aphasia from a posterior left temporal lesion, probably in the middle cerebral artery territory.
- Check the visual field: Look for a superior quadrantanopia from radiation damage; right-sided sensory loss may occur if the lesion extends into the parietal lobe.
- Arrange imaging: Urgent CT or MRI and vascular imaging are arranged.
- Contrast Broca aphasia: A man with right arm weakness whose speech is slow, effortful and telegraphic, yet who understands every question, has Broca aphasia from an inferior frontal lesion.
- Recognise conduction aphasia: A patient with fluent speech, good understanding and a repetition deficit, who repeats "no ifs, ands or buts" as "no if, and, or but", has conduction aphasia and a lesion of the arcuate fasciculus.
Where the mnemonics mislead
Repetition is the most useful single test, and the usual mnemonic is incomplete.
- Trap: trusting the mnemonic that Broca speaks and Wernicke understands. Correct: the real discriminators are fluency together with comprehension, and repetition is what separates conduction aphasia.
- Trap: treating dysarthria as aphasia. Correct: dysarthria is a motor speech disorder with normal language content, whereas aphasia affects the language itself.
- Trap: assuming a right-sided lesion excludes aphasia. Correct: a left-handed patient may have atypical language localisation, so a right-sided lesion does not exclude aphasia in that patient.
- Trap: naming Gerstmann syndrome from a single feature. Correct: the full tetrad of finger agnosia, left-right disorientation, dysgraphia and acalculia, from a dominant parietal lesion, is the expected answer.
Frequently asked questions
What distinguishes Broca aphasia from Wernicke aphasia?
Broca aphasia is non-fluent with preserved comprehension, usually from an inferior frontal lesion, while Wernicke aphasia is fluent with impaired comprehension, usually from a posterior superior temporal lesion. Both show impaired repetition, which is why fluency and comprehension must be assessed alongside it.
What is the key feature of conduction aphasia?
Conduction aphasia is fluent speech with good comprehension but disproportionately impaired repetition, with phonemic paraphasias. It usually results from a lesion of the arcuate fasciculus, and patients often recognise and correct their own errors.
Which visual field defect follows a temporal lobe lesion?
Damage to Meyer loop fibres in the temporal lobe produces a contralateral superior quadrantanopia, sometimes called a pie-in-the-sky defect. Parietal lesions in the optic radiation produce the opposite inferior quadrantanopia.
What are the four features of Gerstmann syndrome?
Finger agnosia, left-right disorientation, agraphia and acalculia together make up Gerstmann syndrome, typically from a lesion of the dominant angular gyrus. The tetrad is best remembered as a set, since isolated features occur in other conditions.