Middle cerebral artery stroke: face and arm weakness with aphasia
Middle cerebral artery (MCA) stroke typically weakens the opposite face and arm; damage to the dominant hemisphere (the side with the speech centres) can add aphasia, a language disorder.
Remember
Weakness of the opposite face and arm, with the leg relatively spared, plus effortful, halting speech with preserved comprehension, points to a stroke of the dominant hemisphere's middle cerebral artery, usually the left.
The middle cerebral artery supplies the outer-facing (lateral) surface of the hemisphere: part of the frontal lobe, plus the sides of the temporal and parietal lobes. That territory (the region an artery supplies) includes the motor and sensory cortex for the face, hand and arm, the strips of cerebral cortex that start voluntary movement and receive touch.
Because motor and sensory pathways cross the midline, the weakness and sensory loss appear on the side opposite the damaged hemisphere. The leg is relatively spared, since the anterior cerebral artery supplies the medial surface where the leg is represented. The pattern is not absolute: if the infarction reaches the internal capsule (the bundle carrying descending motor fibres), the whole side can be weak, leg included.
Aphasia appears only if the dominant hemisphere is damaged, because both speech and language centres lie there. That is the left hemisphere in most people.
Broca's area lies in the frontal lobe and produces speech. Damage gives non-fluent (expressive) aphasia: effortful, halting speech in short phrases, with comprehension preserved. Wernicke's area lies in the temporal lobe and adjacent parietal lobe, and it handles comprehension of speech. Damage gives fluent (receptive) aphasia: words flow but make no sense, often called 'word salad', and understanding is poor.
The MCA also supplies the optic radiations (the visual pathway through the temporal and parietal lobes), so a contralateral homonymous hemianopia (the same half of the visual field is lost in both eyes) can occur.
Key facts
- Territory
- the lateral frontal, temporal and parietal lobes, plus the basal ganglia (involved in motor control) and the internal capsule.
- Weakness and sensory loss
- in the opposite face and arm, with the leg relatively spared.
- Exception
- if the infarct reaches the internal capsule, the leg can be weak as well.
- Dominance
- aphasia occurs only if the dominant hemisphere, usually the left, is damaged.
- Broca's and Wernicke's aphasias
- Broca's aphasia is non-fluent with preserved comprehension, while Wernicke's aphasia is fluent but meaningless, with poor comprehension.
- Non-dominant side
- a non-dominant hemisphere infarction of the MCA would not cause aphasia but could cause hemispatial neglect (not attending to one side of the world).
Exam traps
- The anterior cerebral artery is the wrong way round: it supplies the medial surface, so its blockage weakens the opposite leg far more than the face and arm.
- The right middle cerebral artery does not fit when the weakness is on the right: it would weaken the left face and arm, and in a right-handed person it would not typically cause aphasia.
- Damage to Broca’s area does not give fluent speech with poor understanding: it produces effortful, halting speech with comprehension preserved, which is the opposite pattern.
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