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A Sample Case: A 45 year old woman with a history of hypertension experienced a brief "blackout". She had complained of severe headaches, nausea, dizziness and a roaring sound in the left ear during the previous day. She also had difficulty walking and called a cab to take her to the hospital.

The physician found her mentally alert and communicative, the external auditory canals were clear and she was physically normal except for an elevated blood pressure of 165/105. Strength in her extremities was generally normal. Her speech was fluent and full of meaning though dysarthric. Nystagmus was present. There was a facial paralysis (upper and lower) on the left side which also had diminished sensation. There was impaired pain and temperature sense from the right side of the body. At rest, her eyes deviated toward the right; on command, there was paralysis of horizonal conjugate gaze to the left. Hearing was diminished on the left side. On the left, the eye drooped and the pupil was constricted.

Explanation -

Dizziness (vertigo), nausea and nystagmus can be the result of injury of the vestibular nerve or nucleus. The roaring sound (tinnitus) with diminished hearing on one side can be the result of injury to the cochlear nerve or nucleus on the left. Paralysis of the muscles of facial expression of the upper and lower face on the left results from injury of the left facial nerve or its motor nucleus. Diminished sensation on the left face suggests injury to the nearby descending tract and nucleus of spinal V. Diminished pain and temperature on the right side of the body is due to injury of the left spinothalamic tracts.

There was difficulty walking though motor strength was generally normal. This awkwardness may be attributable to injury of the left middle cerebellar peduncle. The drooping eyelid and constricted pupil suggest a Horner's syndrome due to injury of descending autonomic fibers in the lateral reticular formation.

The vestibulo-cochlear nerve/nuclei, the facial nerve/nucleus, tract/nucleus of spinal V, spinothalamic tract and middle cerebellar peduncle all lie laterally in the pons within the area of supply of the anterior inferior cerebellar artery.