No, the mouth will deviate AWAY from the side of the stroke (to the LEFT in a right MCA stroke)
In a patient with a right middle cerebral artery (MCA) stroke, the mouth will deviate to the LEFT (away from the lesion side), not to the right. This occurs because the right motor cortex controls the left side of the face, and when damaged, the unopposed action of the intact left motor cortex pulls the mouth toward the unaffected (left) side.
Understanding the Neuroanatomy
The motor cortex in each hemisphere controls the contralateral (opposite) side of the body through the corticobulbar tract. In a right MCA stroke:
- The right motor cortex is damaged
- This causes weakness of the LEFT facial muscles (contralateral hemiparesis)
- The intact LEFT motor cortex continues to function normally
- The stronger, unaffected right facial muscles pull the mouth toward the LEFT side
- Result: mouth deviation AWAY from the stroke side
Clinical Presentation of Right MCA Stroke
Patients with right MCA stroke typically present with 1, 2:
- Left-sided hemiplegia (face, arm, and leg weakness)
- Left hemisensory loss
- Conjugate eye deviation to the RIGHT (eyes look toward the lesion)
- Left homonymous hemianopia
- Left hemineglect (more prominent with right hemisphere lesions)
- Reduced consciousness in severe cases
The combination of these symptoms has a positive predictive value of 0.73 for large MCA infarction 1.
Important Clinical Pitfall
Do not confuse the direction of mouth deviation with the side of the stroke. The mouth deviates TOWARD the intact side (away from the lesion). This is opposite to the direction of eye deviation, where the eyes look TOWARD the lesion side ("eyes look at the lesion, mouth looks away from the lesion").
Monitoring for Malignant Edema
Right MCA strokes warrant close monitoring as they can progress to malignant cerebral edema 3, 2:
- Peak edema occurs 2-4 days post-stroke (can extend beyond 96 hours)
- Warning signs: progressive headache, vomiting, declining consciousness, pupillary changes
- Mortality without intervention: up to 80% in conservatively treated patients
- Decompressive hemicraniectomy reduces mortality by approximately 50% when performed within 48 hours in appropriate candidates 3
Right hemispheric MMCA strokes are actually more common (63% of cases) than left-sided and are associated with higher morbidity despite similar mortality rates 4.