R1 responses of the trigeminofacial reflex in lesions extrinsic to the brain stem.

Isolated or prevalent impairment of the trigeminofacial reflex (tfr) has been described both in pontine lesions and in lesions extrinsic to the brain stem. No satisfactory explanation of this finding in extrinsic lesions has ever been put forward. In a series of patients with lesions outside the brain stem together with selective or prevalent R1 impairment reported here this finding can be explained by the peculiar anatomy of the various nerve fibers in the trigeminal sensory root.