Lesions to Cranial Nerves

• CN III
• Weber’s Syndrome
• Ventral midbrain where CN III exits by the cerebral peduncle
• CN III palsy with contralateral hemiplegia
• Benedikt’s Syndrome
• Weber’s with contralateral tremor, ataxia, and chorea
• Involves the red nucleus
• CN IV
• Causes vertical diplopia maximal on attempted downgaze to the contralateral side
• Patient tilts head laterally to opposite side
• Superior colliculi
• Unilateral lesions
• Neglect of contralateral visual field
• Heightened responses to stimuli in ispilateral field
• Deficits in tracking
• No impairment of eye movements
• Stimulation causes contralateral conjugate deviation of the eyes
• Inferior colliculi – auditory relay nuclei
• CN VI
• Only cranial nerve in which lesion of nerve (ipsilateral lateral rectus palsy) causes different clinical effect from lesion of nucleus (ipsilateral lateral rectus palsy AND contralateral medial rectus palsy)
• CN VII
• can determine location by symptoms
• Greater petrosal nerve is the first to split off
• Nerve to the stapedius muscle is the second to spit off
• Chorda tympani is the third to split off
• Motor fibers to face remain
• “crocodile tears” – aberrant regeneration of the nerve to the greater petrosal nerve instead of the submandibular ganglion
• cry when salivation impulse is sent
• Transverse crest – separates cochlear and inferior vestibular nerves from facial and superior vestibular nerves
• Bill’s Bar – separates superior vestibular from facial nerve (perpencidular to transverse crest)
• Bell’s Palsy – Most common form of facial paralysis; facial weakness typically evolves over 12-48 hours
• Incidence is 23/100,000 population
• 80% fully recover over weeks to months; treatment involves appropriate eye protective care and steroids
• CN VIII – hearing loss, vertigo
• CN X, IX – asymmetric palate elevation
• CN XI
• weakness turning head to the opposite side and downward and outward
• rotation of the scapula
• moderate sagging of the shoulder
• CN XII – Tongue deviates toward side of lesion