A 34-year-old man is evaluated in the clinic due to persistent buzzing in his right ear for the past 6 months. The patient also has decreased hearing on the right side. He has had no fever, ear pain, runny nose, sore throat, or cough. The patient does not use cotton swabs and has not been exposed to loud noise. He tried using over-the-counter oral pseudoephedrine with no improvement in his symptoms. On physical examination, there is no sinus tenderness, and mucous membranes are moist without erythema or exudate. Otoscopic examination reveals normal-appearing external auditory canals bilaterally with pinkish-grey tympanic membranes. MRI of the brain reveals an intracranial tumor. This patient's lesion has most likely arisen from which of the following structures?

Question

A 34-year-old man is evaluated in the clinic due to persistent buzzing in his right ear for the past 6 months.  The patient also has decreased hearing on the right side.  He has had no fever, ear pain, runny nose, sore throat, or cough.  The patient does not use cotton swabs and has not been exposed to loud noise.  He tried using over-the-counter oral pseudoephedrine with no improvement in his symptoms.  On physical examination, there is no sinus tenderness, and mucous membranes are moist without erythema or exudate.  Otoscopic examination reveals normal-appearing external auditory canals bilaterally with pinkish-grey tympanic membranes.  MRI of the brain reveals an intracranial tumor.  This patient's lesion has most likely arisen from which of the following structures?

Quizplus · Accepted Answer

11ec160b_35d2_c776_9249_df5287fc1082_MD0001_00 This patient's clinical presentation is suggestive of acoustic neuroma, a Schwann cell-derived tumor that typically arises from the vestibular portion of the vestibulocochlear nerve (CN VIII). The vestibulocochlear nerve exits the brainstem from the pontomedullary junction, lateral to the facial nerve, and enters the cerebellopontine angle (between the cerebellum and lateral pons). Patients with acoustic neuroma usually have ipsilateral sensorineural hearing loss and tinnitus (ear ringing/buzzing) due to impairment of the cochlear portion of the nerve. Damage to the vestibular component may also result in vertigo, dysequilibrium, and nystagmus. Most cases present unilaterally, but bilateral acoustic neuromas are frequently seen in patients with neurofibromatosis type 2. (Choice A) The trigeminal nerve (CN V) exits the brainstem from the ventrolateral pons. Injury to CN V may cause ipsilateral loss of facial sensation and the corneal reflex (afferent limb) and paralysis of the muscles of mastication. (Choice B) The abducens nerve (CN VI) exits the brainstem from the pontomedullary junction medial to the facial nerve. Injury to CN VI may result in the inability to abduct the ipsilateral eye and horizontal diplopia (lack of innervation to the lateral rectus). (Choice C) The facial nerve (CN VII) exits the brainstem from the ventrolateral pontomedullary junction, just lateral to the abducens nerve. Damage to CN VII may result in ipsilateral facial muscle paralysis (upper and lower), loss of the corneal reflex (efferent limb), loss of taste in the anterior two-thirds of the tongue, and hyperacusis (lack of innervation to the stapedius). (Choice E) The glossopharyngeal nerve (CN IX) exits the brainstem from the postolivary sulcus in the medulla just rostral to the vagus nerve. Injury to CN IX may result in loss of taste/sensation in the posterior one-third of the tongue and absent gag reflex (afferent limb). (Choice F) The vagus nerve (CN X) exits the brainstem from the postolivary sulcus just caudal to the glossopharyngeal nerve. Damage to CN X may cause dysphonia (lack of innervation to the laryngeal muscles), impaired swallowing with inability to elevate the soft palate (lack of innervation to the pharyngeal muscles), and loss of the gag reflex (efferent limb). (Choice G) Fibers of the spinal accessory nerve (CN XI) exit from the lateral medulla and upper segments of the cervical spinal cord. Injury to CN XI can cause weakness on head rotation away from the side of the lesion (lack of innervation to the sternocleidomastoid) and ipsilateral shoulder droop (lack of innervation to the trapezius). Educational objective: Acoustic neuromas are Schwann cell-derived tumors that typically arise from the vestibular portion of the vestibulocochlear nerve and are commonly located at the cerebellopontine angle (between the cerebellum and lateral pons). Patients usually present with unilateral sensorineural hearing loss and tinnitus. __________ References: Management of sporadic vestibular schwannoma. (http://www.ncbi.nlm.nih.gov/pubmed/25886814) Otologic manifestations of acoustic neuroma. (http://www.ncbi.nlm.nih.gov/pubmed/25578127)

A 34-Year-Old Man Is Evaluated in the Clinic Due to Persistent