Benedikt’s syndrome results from a unilateral lesion limited to the midbrain tegmentum that includes the fibers of the oculomotor nerve, red nucleus, superior cerebellar peduncle, medial lemniscus, and spinothalamic tract (see Fig. 17.3C). Damage to the red nucleus and fibers of the superior cerebellar peduncle, which pass through and around it, results in cerebellar signs such as coarse intention tremor, dysdiadochoki-nesis, cerebellar ataxia, and hypotonia on the contralateral side of the body (Chap. 7). The injury to the third cranial nerve causes a LMN paralysis of the ipsilateral extraocular muscles innervated by the oculomotor nerve and a dilated pupil (mydriasis) because of loss of parasympathetic fibers (see Basal Region of the Midbrain). The eye cannot be adducted beyond the midline, elevated or lowered.

Interruption of the crossed spinothalamic tract, trigeminothalamic tract, and medial lemniscus results in the loss of sense of pain, temperature, light touch, vibratory sense, pressure touch, and other discriminatory senses on the opposite side of the body and head. Touch and other discriminatory senses on the contralateral side of the forehead can be retained if the uncrossed posterior trigeminothalamic tract is intact.

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