Left buccal residue with limited left lower face movement but intact bilateral forehead indicates a lesion in which location?

• A. Left cortical lesion
• B. Right cortical lesion
• C. Left peripheral lesion
• D. Right peripheral lesion

Answer: (B)

The pattern being tested is how facial weakness localizes a lesion using upper motor neuron versus lower motor neuron pathways. Forehead movement is bilaterally innervated, so a unilateral cortical (or corticobulbar) lesion typically spares the forehead but weakens the lower face on the opposite side. In this case, the left lower face is weak while the forehead moves normally on both sides, which points to a lesion in the right hemisphere's cortex or its corticobulbar connections. That right-sided lesion would produce contralateral (left) oral and lower-face weakness, matching the left buccal residue and limited left lower-face movement. A left cortical lesion would cause right lower-face weakness, not left, and a peripheral facial nerve lesion would distort both forehead and lower-face movements on the same side, which is not seen here.