Expected Deficits with Right MCA Branch Acute Infarct in the Right Frontal Lobe
An acute right middle cerebral artery branch infarct involving the frontal lobe will primarily cause left-sided motor weakness (contralateral hemiparesis), left-sided sensory loss, left visual field deficits, and importantly, neglect syndromes, acute confusional states, and altered emotional processing—particularly blunted pleasant emotions—which are often subtle and underrecognized.
Motor and Sensory Deficits
The most obvious deficits will be contralateral (left-sided) motor weakness, ranging from mild drift to complete hemiplegia depending on infarct size. The arm is typically more affected than the leg in MCA territory strokes 1. Expect:
- Left arm and facial weakness (face-arm predominance)
- Left-sided sensory loss affecting face, arm, and potentially leg
- Left visual field defect (hemianopia) if the infarct extends posteriorly
Use the NIHSS to systematically quantify these deficits—assess motor function with drift testing, facial symmetry, and sensory responses 1.
Cognitive and Behavioral Deficits (Often Missed)
Right frontal MCA infarcts produce distinctive cognitive deficits that are frequently underdiagnosed:
Acute Confusional State
Right MCA infarcts commonly present with acute confusional states due to disruption of selective attention mechanisms 2. Patients appear disoriented and confused, which can be mistaken for delirium from other causes. This represents a primary deficit in selective attention arising from damage to association cortex convergence areas 2.
Neglect and Inattention
Expect left-sided neglect (extinction or inattention on NIHSS item 11) 1. Test by:
- Simultaneous bilateral stimulation (visual and tactile)
- Asking patient to draw or bisect lines
- Observing whether patient attends to left side of space
Emotional Changes
Right MCA strokes alter emotional processing, particularly reducing pleasant emotional experiences 3. This occurs through:
- Decreased activity in the anterior cingulate cortex (ACC) ipsilaterally
- Reduced activity in thalamus, dorsal and medial prefrontal cortex
- Impaired emotional awareness, limiting patients' ability to report these changes 3
These emotional deficits are subtle but clinically significant for quality of life and rehabilitation.
Personality and Executive Function Changes
Right frontal involvement may cause:
Gaze Deviation
Look for conjugate gaze deviation to the right (toward the lesion side), indicating frontal eye field involvement 1.
Clinical Pitfalls
The most common error is missing the cognitive and behavioral deficits because:
- Motor deficits are obvious and dominate the clinical picture
- Confusional states are attributed to other causes (infection, medications)
- Emotional awareness is impaired, so patients don't report emotional changes 3
- Neglect is not systematically tested
Always formally test for neglect and assess attention/orientation carefully in right hemisphere strokes 1. Document baseline NIHSS including items 1A-C (consciousness, orientation, commands) and item 11 (extinction/inattention).
Prognosis Considerations
If the infarct is large (>50% MCA territory), monitor closely for:
- Malignant edema developing over 1-5 days 5
- Progressive decreased consciousness
- Midline shift and herniation risk 5
Younger patients (<60 years) with large infarcts are at highest risk for fatal brain edema 6. Early signs include headache, vomiting, and declining consciousness beyond what the initial stroke would predict 5.