Anterior cerebral artery stroke: leg-predominant weakness and frontal features
Anterior cerebral artery stroke affects the medial frontal lobe and the front of the parietal lobe: weakness mainly of the opposite leg, with apathy (loss of drive) or poor planning.
Remember
An anterior cerebral artery stroke typically weakens the opposite leg more than the arm or face, and it can also cause apathy, poor planning or urinary incontinence.
Memory aid
picture the homunculus folded over the top of the brain, with the leg tucked down the middle groove that the ACA supplies
The body map is folded over the top of the brain, so the leg lies in the midline groove supplied by this artery.
The anterior cerebral artery (ACA) supplies the medial (inner) surface of the frontal lobe and the front of the parietal lobe, the part of each hemisphere that lies along the midline. It also supplies the corpus callosum, the thick band of fibres joining the two hemispheres.
Within this territory sits the paracentral lobule, the strip of primary motor and sensory cortex for the opposite leg. The body map on the cortex (the homunculus) places the leg on the medial surface, while the face and arm lie on the outer surface supplied by the middle cerebral artery. Motor and sensory pathways cross the midline, so an ACA stroke affects the opposite side; because the leg area lies on the medial surface, the weakness and numbness are typically worse in the leg than in the arm or face. In an ACA stroke, right leg signs mean the left ACA is affected.
The prefrontal cortex, which also lies in this territory, controls executive function (planning, decision making and personality), so damage causes apathy (loss of drive) and poor planning. The paracentral lobule also helps control the bladder, so urinary incontinence can occur.
An ACA stroke involving the medial frontal regions or the corpus callosum can impair purposeful movement. Apraxia is the inability to plan and carry out learned movements even though strength is adequate. A callosal disconnection (loss of the link between the hemispheres) may cause left-hand apraxia, including after a right ACA stroke.
Key facts
- Territory
- the medial and superior frontal lobe and the anterior parietal lobe, including the paracentral lobule.
- Classic deficit
- contralateral (opposite-sided) weakness and sensory loss, greater in the leg than in the arm or face.
- Side
- the weakness is on the opposite side to the stroke, so right leg signs mean a left ACA stroke.
- Frontal features
- apathy, poor planning and personality change can occur.
- Personality change
- often noticed only in the long term, because the stress of the acute phase can mask it.
- Bladder
- ischaemia (shortage of blood supply) in the paracentral lobule can cause urinary incontinence.
Exam traps
- Weakness of the face and arm with the leg less affected is not the anterior cerebral artery pattern; it fits the middle cerebral artery, which supplies the outer surface where the face and arm lie.
- A left anterior cerebral artery stroke weakens the right leg, not the left, so the side does not match left leg weakness.
- Strokes of the anterior choroidal artery mainly cause weakness, but they would not explain apathy and difficulty planning, because it is a small artery that supplies deep structures rather than the frontal cortex.
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