Supranuclear Cortical Lesions

Anatomical Definition and Clinical Significance

Supranuclear lesions are distinguished from nuclear or infranuclear lesions by their characteristic pattern of sparing upper facial muscles due to bilateral cortical innervation, whereas lower motor neuron lesions cause complete ipsilateral facial weakness including forehead involvement, as noted by the American Academy of Neurology 1, 2, 3.
Supranuclear facial palsy preserves forehead movement because upper facial muscles receive bilateral cortical input, according to the American Academy of Neurology 2, 3.
Peripheral facial nerve lesions result in complete ipsilateral facial paralysis, including inability to close the eye or wrinkle the forehead, as reported by the American Academy of Neurology 1, 2.

Cortical lesions in multiple sclerosis are classified histopathologically into four types: Type I (leukocortical), Type II (small perivenous intracortical), Type III (subpial demyelination), and Type IV (extending through full cortical width), as classified by the National Multiple Sclerosis Society 5, 6, 7.
These lesions appear as hyperintensity on DIR sequences compared to normal grey matter, requiring at least 3mm size along the main axis, according to the National Multiple Sclerosis Society 5, 6, 8.
Curvilinear/worm-shaped cortical lesions following sulcal and gyral contours are pathognomonic for multiple sclerosis, as noted by the National Multiple Sclerosis Society 7, 9, 10.

The key clinical distinction is forehead involvement: preserved forehead function indicates supranuclear pathology, while complete forehead paralysis indicates nuclear or infranuclear pathology, as reported by the American Academy of Neurology 2, 3.
Multiple cranial nerve involvement suggests pontine lesion location, according to the American Academy of Neurology 2.
Combined CN VII and CN XII palsy with ipsilateral tongue deviation indicates skull base or extracranial pathology, not supranuclear cortical lesions, as noted by the American Academy of Neurology 1, 2.
MRI with contrast is mandatory for localizing lesions when multiple cranial nerves are involved or when clinical examination suggests central pathology, as recommended by the American Academy of Neurology 1, 2, 3.