Pons
Lesions

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1) NEOPLASMS - ACOUSTIC NEUROMA

A Sample Case: A 50 year old woman became aware that she could not feel the pressure of her mascara pencil on her right eyelid. She was already aware that her hearing was better on her left side than her right, from which she often was aware of a "ringing". She was troubled by a continuous sense of dizziness.

The neurologic exam confirmed that she had diminished hearing on the right side and upon questioning revealed that she suffered from headaches in addition to noting pain on the right side of her face. The woman had difficulty standing without swaying when her heels were together, whether her eyes were open or closed; her gait was slightly unsteady. She had a flat nasolabial fold on the right as well a weakness in wrinkling the forehead on that side. Nystagmus was elicited when looking to the right and she showed a loss of the right corneal reflex. Other cranial nerves and motor and sensory findings from arms, legs, and trunk were within normal limits. Radiologic imaging confirmed a diagnosis of acoustic neuroma in the cerebellopontine angle.

Explanation -

The tumor growing on the right 8th nerve produces auditory nerve irritation (ringing) and neuron death (deafness). Dizziness, nystagmus, nausea, and vomiting are signs of vestibular nerve involvement. Facial pain and loss of the corneal reflex on the right are also consistent with involvement of the sensory division of the 5th nerve on the right. Weakness of the muscles of the upper and lower face on the right implicates the motor division of the 7th nerve. Unsteadiness in standing and walking is attributable to involvement of the nearby cerebellar peduncles or the cerebellum. The evidence mostly indicates involvement of the peripheral divisions of the 5th, 7th and 8th cranial nerves and the cerebellum. This is a tumor derived by a overgrowth of Schwann cells originating on the vestibular nerve of the 8th nerve just within the internal auditory canal. As it grows the tumor extends into the posterior cranial fossa to the angle between the cerebellum and the pons. In this lateral position it compresses the 5th, 7th and, less often, the 9th and 10th cranial nerves.