SECTION VII THE NERVOUS SYSTEM Acoustic Neurinoma A 47-year-old man saw his family physician because of headaches and an unsteady gait.The patient had a long history of difficulties with hearing in his right ear. Fourteen years previously,he experienced a ringing in that ear,but since then he had become progressively more deaf on the right side.In addition,his gait became unsteady,and he tended to fall toward the right.Five years ago,he developed numbness on the right side of his face,and this has since spread to include the right half of the tongue.A year ago,he developed pain in the occipital area,and he sometimes became nauseated.The right side of his face became weak,and it was observed that his right eye constantly remained open.The neurologic examination revealed the following abnormalities.The right eyelid was open and seldom blinked, and the right side of the face was immobile.The right corneal reflex was absent. Taste was lost on the right side of the tongue.The right eye could not be deviated to the right beyond the midline.Nystagmus appeared when the patient moved his eyes horizontally.Sensation was lost on right side of the face.When the patient was asked to say "ah,"the soft palate deviated to the left.Examination of the eyes with an ophthalmoscope revealed papilledema bilaterally.The patient walked with a wide stance,and he lurched to the right.His right arm showed incoordination in the finger-to-nose test.An audiogram showed a complete hearing loss for the right ear,and a caloric test was completely negative on the right.Eighth nerve function was normal for the left ear.In the Weber test,sound was localized to the left ear; the Rinne test was normal for the left ear,but no sound was heard on the right. The patient was referred to a neurosurgeon for removal of an acoustic neurinoma. 1.What cranial nerves were affected in this patient? 2.What accounts for the headaches,papilledema,and nausea? 3.Is the type of deafness conductive or sensorineural?
SECTION VII THE NERVOUS SYSTEM Acoustic Neurinoma A 47-year-old man saw his family physician because of headaches and an unsteady gait. The patient had a long history of difficulties with hearing in his right ear. Fourteen years previously, he experienced a ringing in that ear, but since then he had become progressively more deaf on the right side. In addition, his gait became unsteady, and he tended to fall toward the right. Five years ago, he developed numbness on the right side of his face, and this has since spread to include the right half of the tongue. A year ago, he developed pain in the occipital area, and he sometimes became nauseated. The right side of his face became weak, and it was observed that his right eye constantly remained open. The neurologic examination revealed the following abnormalities. The right eyelid was open and seldom blinked, and the right side of the face was immobile. The right corneal reflex was absent. Taste was lost on the right side of the tongue. The right eye could not be deviated to the right beyond the midline. Nystagmus appeared when the patient moved his eyes horizontally. Sensation was lost on right side of the face. When the patient was asked to say "ah," the soft palate deviated to the left. Examination of the eyes with an ophthalmoscope revealed papilledema bilaterally. The patient walked with a wide stance, and he lurched to the right. His right arm showed incoordination in the finger-to-nose test. An audiogram showed a complete hearing loss for the right ear, and a caloric test was completely negative on the right. Eighth nerve function was normal for the left ear. In the Weber test, sound was localized to the left ear; the Rinne test was normal for the left ear, but no sound was heard on the right. The patient was referred to a neurosurgeon for removal of an acoustic neurinoma. 1. What cranial nerves were affected in this patient? 2. What accounts for the headaches, papilledema, and nausea? 3. Is the type of deafness conductive or sensorineural?
4.Explain the negative caloric test on the right. 5.Explain the loss of taste on the right side of the tongue. 6.Explain the loss of sensation on the right side of the face. 7.Account for the lurching gait and the ataxia of the right arm. ANSWER 1.Acoustic neurinomas are slowly growing tumors of Schwann cells of the eighth cranial nerve.As they enlarge,they can cause loss of function of adjacent cranial nerves and also damage the cerebellum and cerebellar peduncles.In this case, deficits occur in the function of several cranial nerves on the right side,including not only the cochlear and vestibular parts of the eighth nerve (see answers to questions 3 and 4),but also the trigeminal nerve (see answer to question 6),the abducens nerve (failure of the right eye to deviate to the right beyond the midline), the facial nerve (see answer to question 5),and the glossopharyngeal and vagus nerves (deviation of the soft palate to the left).The right cerebellum is also damaged (gait disorder and ataxia of the right arm). 2.Large acoustic neurinomas (or other mass lesions)cause an increase in intracranial pressure.This distorts the meninges and therefore induces pain transmission in the trigeminal system and results in headaches.Papilledema or swelling of the optic nerve head is caused by compression of the venous drainage from the retina through veins that course in the optic nerve.This condition can cause blindness.Nausea often accompanies increases in intracranial pressure and may be caused by pressure on the brainstem. 3.The type of deafness is sensorineural.Conduction deafness is generally not complete.The Weber test is conducted by placing the stem of a vibrating tuning fork in contact with the midline of the forehead or on the vertex of the skull.Normally, the sound can be heard equally well in both ears.In conductive hearing loss,the sound is heard better in the defective ear,whereas in sensorineural hearing loss the sound is louder in the normal ear.The Rinne test determines if air or bone
4. Explain the negative caloric test on the right. 5. Explain the loss of taste on the right side of the tongue. 6. Explain the loss of sensation on the right side of the face. 7. Account for the lurching gait and the ataxia of the right arm. ANSWER 1. Acoustic neurinomas are slowly growing tumors of Schwann cells of the eighth cranial nerve. As they enlarge, they can cause loss of function of adjacent cranial nerves and also damage the cerebellum and cerebellar peduncles. In this case, deficits occur in the function of several cranial nerves on the right side, including not only the cochlear and vestibular parts of the eighth nerve (see answers to questions 3 and 4), but also the trigeminal nerve (see answer to question 6), the abducens nerve (failure of the right eye to deviate to the right beyond the midline), the facial nerve (see answer to question 5), and the glossopharyngeal and vagus nerves (deviation of the soft palate to the left). The right cerebellum is also damaged (gait disorder and ataxia of the right arm). 2. Large acoustic neurinomas (or other mass lesions) cause an increase in intracranial pressure. This distorts the meninges and therefore induces pain transmission in the trigeminal system and results in headaches. Papilledema or swelling of the optic nerve head is caused by compression of the venous drainage from the retina through veins that course in the optic nerve. This condition can cause blindness. Nausea often accompanies increases in intracranial pressure and may be caused by pressure on the brainstem. 3. The type of deafness is sensorineural. Conduction deafness is generally not complete. The Weber test is conducted by placing the stem of a vibrating tuning fork in contact with the midline of the forehead or on the vertex of the skull. Normally, the sound can be heard equally well in both ears. In conductive hearing loss, the sound is heard better in the defective ear, whereas in sensorineural hearing loss the sound is louder in the normal ear. The Rinne test determines if air or bone
conduction is heard best.The stem of a vibrating tuning fork is placed on the mastoid process.When the sound is no longer heard,the tuning fork is removed from the bone, and the fork is brought close to the ear.Normally,the sound is still heard, indicating that air conduction is better than bone conduction.In conductive hearing loss,bone conduction is better than air conduction.The Rinne test was not very helpful in this case because the deafness was complete;in cases of a partial sensorineural hearing loss,the Rinne test is positive (i.e.,hearing is best for air conduction). 4.The caloric test is used to examine vestibular function.When cold water is placed in the external auditory canal of one ear (with the head tilted back to bring the horizontal semicircular canals into the vertical plane),nystagmus will normally develop,and the fast phase of the nystagmus will be toward the opposite ear.Warm water will produce nystagmus with the fast phase toward the ear that is irrigated. In this case,no nystagmus was produced when a caloric test was done on the right side,because the vestibular part of the eighth cranial nerve was interrupted along with the acoustic part of the nerve. 5.The acoustic neurinoma in this case caused a loss of function in the nearby facial,glossopharyngeal,and vagus nerves.The result was not only loss of the motor functions of these cranial nerves (paralysis of the right side of the face,including the levator of the eyelid,and weakness of the soft palate on the right),but also loss of taste on the right side of the tongue.The patient would not have noticed this loss of taste because substances in the mouth would have stimulated taste buds on the left side of the tongue.However,a loss of taste can be determined in a careful neurologic examination. 6.General sensation was lost on the right side of the face and tongue because the tumor damaged the sensory portion of the right trigeminal nerve. 7.The gait disturbance and ataxia of the right arm were caused by compression by the tumor of the cerebellar peduncles and cerebellum on the right side
conduction is heard best. The stem of a vibrating tuning fork is placed on the mastoid process. When the sound is no longer heard, the tuning fork is removed from the bone, and the fork is brought close to the ear. Normally, the sound is still heard, indicating that air conduction is better than bone conduction. In conductive hearing loss, bone conduction is better than air conduction. The Rinne test was not very helpful in this case because the deafness was complete; in cases of a partial sensorineural hearing loss, the Rinne test is positive (i.e., hearing is best for air conduction). 4. The caloric test is used to examine vestibular function. When cold water is placed in the external auditory canal of one ear (with the head tilted back to bring the horizontal semicircular canals into the vertical plane), nystagmus will normally develop, and the fast phase of the nystagmus will be toward the opposite ear. Warm water will produce nystagmus with the fast phase toward the ear that is irrigated. In this case, no nystagmus was produced when a caloric test was done on the right side, because the vestibular part of the eighth cranial nerve was interrupted along with the acoustic part of the nerve. 5. The acoustic neurinoma in this case caused a loss of function in the nearby facial, glossopharyngeal, and vagus nerves. The result was not only loss of the motor functions of these cranial nerves (paralysis of the right side of the face, including the levator of the eyelid, and weakness of the soft palate on the right), but also loss of taste on the right side of the tongue. The patient would not have noticed this loss of taste because substances in the mouth would have stimulated taste buds on the left side of the tongue. However, a loss of taste can be determined in a careful neurologic examination. 6. General sensation was lost on the right side of the face and tongue because the tumor damaged the sensory portion of the right trigeminal nerve. 7. The gait disturbance and ataxia of the right arm were caused by compression by the tumor of the cerebellar peduncles and cerebellum on the right side