Meningioma of the Acoustic Nerve Case File

Meningioma of the Acoustic Nerve Case File

Eugene C. Toy, MD, Ericka Simpson, MD, Pedro Mancias, MD, Erin E. Furr-Stimming, MD

CASE 52

A 43-year-old right-handed woman presents to the office with hearing loss, facial paralysis, and headache. Her history began 1 month ago with a sudden decrease in hearing from her right ear. One week prior to this visit, she noticed weakness of the right face, which has now progressed to complete paralysis. Over the last 3 months she has had intermittent right occipital headache, and clumsiness and imbalance if she turns quickly. She denies any change in her voice or difficulty with swallowing. Her past medical history is unremarkable. She is not on any medications except birth control pills. Her physical examination shows an obvious right facial paralysis. Her pulse is 62 beats/min; blood pressure is 118/62 mm Hg; and temperature is 36.7°C (98.6°F). The head and face have no lesions. Her voice is normal, but her speech is slightly distorted because of the facial paralysis. Her extraocular movements are normal. Her eye grounds do not show any papilledema. Her ears have normal tympanic membranes. The Weber tuning fork lateralizes to the left ear. Air conduction is louder than bone conduction in both ears. There is no neck lymphadenopathy or other masses. There are no cerebellar signs. The remaining physical examination, including the neurologic examination, is normal. An audiogram shows a mild sensorineural hearing loss in the right ear; the left ear has normal hearing. An auditory brainstem response (ABR) is abnormal for the right ear; it is normal for the left ear.

▶ What is the most likely neuroanatomic site of disease and diagnosis?

▶ What is the next diagnostic step?

ANSWERS TO CASE 52:

Meningioma of the Acoustic Nerve                                                 

Summary: A 43-year-old woman has a history of headache, right-sided hearing loss, and right-sided facial paralysis of 1-month duration. The physical examination and ABR tests indicate a sensorineural hearing loss of the right side.

• Most likely neuroanatomic etiology and diagnosis: Cerebellopontine angle (CPA) tumor, with the most common tumors being acoustic neuroma and meningioma
• Next diagnostic step: Magnetic resonance imaging (MRI) with gadolinium

ANALYSIS

Objectives

1. Learn the most common tumors that occur in the CPA.
2. Learn the most common imaging features of these tumors.
3. Learn the available treatment options for these tumors.

Considerations

This 43-year-old woman has symptoms of progressive right-sided hearing loss, facial paralysis, and headache. She also has symptoms of imbalance and disequilibrium. The most common cause of facial nerve paralysis is Bell palsy; however, this patient also has hearing loss, balance issues, and headache, which point to a central rather than peripheral disorder. The ABR confirms an abnormal cranial nerve VIII (or cochlear) function. Patients who present with the combination of hearing loss and facial paralysis demand evaluation by diagnostic imaging to assess for a central nervous system lesion. This patient’s symptoms strongly suggest an abnormality in the CPA. Modern imaging techniques have revolutionized the evaluation of this area. MRI with contrast can readily differentiate the various pathologic processes that occur in this area (Table 52–1).

APPROACH TO:

Cerebellopontine Angle Tumors                                           

DEFINITIONS

ACOUSTIC NEUROMA: A benign tumor that is derived from Schwann cells and arise from the vestibular portion of the acoustic nerve. This is the most common tumor found in the CPA.

AUDITORY BRAINSTEM RESPONSE (ABR): An electrical-evoked hearing test. In this test, electrodes are placed on each ear lobe and on the forehead. A stimulus sound (either a click or tone burst) is delivered into the test ear at a specified loudness; an attached computer captures the electrical brain activity that results from this stimulus and filters out background noise.

BELL PALSY: Idiopathic facial weakness.

CEREBELLOPONTINE ANGLE (CPA): The anatomic space between the cerebellum, pons, and temporal bone. This space contains cranial nerves V through XI.

CONDUCTIVE HEARING LOSS: A form of hearing loss that results from a defect in the sound-collecting mechanism of the ear. These structures include the ear canal, tympanic membrane, middle ear, and ossicles.

MENINGIOMA: Common benign extra-axial tumors of the coverings of the brain. The cell of origin is probably from arachnoid villi. Several histologic subtypes are described: syncytial, transitional, fibroblastic, angioblastic, and malignant.

SENSORINEURAL HEARING LOSS: A form of hearing loss that results from an abnormality in the cochlea or auditory nerve.

CLINICAL APPROACH

Tumors of the Cerebellopontine Angle

CPA tumors are the most common neoplasms of the posterior fossa and account for 7% to 10% of intracranial tumors. Most CPA tumors are benign, with the most common being acoustic neuromas and vascular malformations. The most common nonacoustic CPA neoplasms are meningiomas and epidermoid tumors.

Acoustic Neuromas

Acoustic neuromas are intracranial tumors arising from the Schwann cell sheath involving either the vestibular or cochlear nerve. These comprise about 80% of the tumors in the CPA. They are diagnosed in about 1 per 100,000 people with a rising incidence, perhaps because of the expanded use of MRI. Autopsy studies show a higher incidence of asymptomatic schwannomas. Although a small fraction of affected individuals has neurofibromatosis, the vast majority have no risk factors. Most acoustic neuromas are slow growing, although a small number will increase in size rapidly. Unilateral hearing loss is the most common presentation, although vertigo, headaches, and facial nerve palsy are also seen.

Meningiomas

Meningiomas are usually benign tumors of mesodermal origin and are attached to the dura. These commonly are located along the sagittal sinus, over the cerebral convexities, and in the CPA. Grossly, they are gray, sharply demarcated, and firm. Microscopically, the cells are uniform with round or elongated nuclei and have a characteristic tendency to whorl around each other. Meningiomas tend to affect women more than men in the middle age. Most meningiomas are asymptomatic and are discovered incidentally on neuroimaging. Clinical presentation of meningioma varies due to the location of the tumor. If it is located in optic pathway, visual field defects are noted. CPA tumor locations are generally associated with sensorineural hearing loss. Spinal meningiomas can present with extremity weakness. MRI usually reveals a dural-based mass with dense homogeneous contrast enhancement. Differentials for such appearance on MRI can be lymphoma, tuberculoma, metastatic carcinoma, inflammatory lesions such as sarcoidosis and granulomatosis. Surgical therapy is optimal, and complete resection is curative. For lesions not amenable to surgery, local or stereotactic radiotherapy can ameliorate symptoms. Small asymptomatic lesions in older patients can be observed. Rarely, meningiomas can be more aggressive and have malignant potential; these tumors tend to have higher mitosis and cellular and nuclear atypia. Surgical therapy followed by radiotherapy should be used in these instances.

Epidermoid tumor: A benign tumor composed of squamous epithelial elements thought to arise from congenital rests.

Glomus tumor: The common name for paraganglioma. This highly vascular tumor arises from neuroepithelial cells. These tumors are further named by the structures that they arise from: glomus tympanicum (middle ear), glomus jugulare (jugular vein), glomus vagale (vagus nerve), and carotid body tumor (carotid artery). A rule of 10% is associated with this tumor: approximately 10% of these tumors produce a catecholamine-like substance, approximately 10% of these tumors are bilateral, approximately 10% are familial, and approximately 10% are malignant (ie, potential to metastasize).

APPROACH TO:

Facial Paralysis                                                         

Facial paralysis is a relatively common disorder. In its most common presentation, facial paralysis occurs as a sudden sporadic cranial mononeuropathy. It is not associated with hearing loss; rather, it might be associated with hyperacusis. This form of facial paralysis, also called Bell palsy, is not associated with middle ear disease, parotid tumor, Lyme disease, or any other known cause of facial paralysis. Essentially, Bell palsy is a diagnosis of exclusion. Generally, a pointed history and detailed physical examination will eliminate most of the differential diagnoses. Likewise, the various causes of hearing loss can be eliminated by a careful physical examination. Disease processes, such as otitis media, cholesteatoma, and otosclerosis, can be eliminated by careful history and physical examination with tuning fork tests. However, to know the type and degree of hearing loss, an audiogram is necessary.

Although it requires patient’s cooperation, the audiogram will give the clinician a very accurate measure of the patient’s hearing level. The audiogram can distinguish between sensorineural and conductive hearing loss. Occasionally, patients have mixed hearing loss, a combination of conductive and sensorineural losses in a single ear. Furthermore, the audiogram can give a clue regarding the presence of retrocochlear hearing loss or hearing loss caused by diseases proximal to the cochlea. Tests that might indicate retrocochlear pathology include speech discrimination, acoustic reflexes, and reflex decay.

DIAGNOSIS

Sensorineural hearing loss can be further evaluated by ABR. This test measures the electrical activity within the auditory pathway, and as such, this test helps to evaluate retrocochlear causes of hearing loss. The ABR has five waves that are numbered I through V, and these are correlated to major neural connections in the auditory pathway. These waves have expected morphologies and occur at predictable latencies. Waves that are absent or delayed are indicative of pathology at that point in the auditory pathway. The interwave latencies (such as I-III, III-V, or I-V) can be compared to the opposite side or to standard norms. Abnormalities on ABR need to be further evaluated by imaging studies.

MRI provides excellent definition of the structures within the posterior fossa. Gadolinium contrast allows additional differentiation of various pathologies. Additionally, newer technology, such as fat suppression and diffusion-weighted imaging, can help to identify pathology (Figure 52–1). The MRI appearances of the most common tumors in the posterior fossa are indicated in Table 52–1.

Although MRI with gadolinium contrast gives excellent resolution for the brain, nerve, and soft tissues, computed tomography (CT) scanning is necessary for bony imaging. Often, both imaging modalities are combined to understand the full extent of the disease process within the skull base.

Figure 52–1. Post-gadolinium T1 MRI with fat suppression. CPA meningioma. (Reproduced, with permission, from Lalwani A. Current Diagnosis and Treatment in Otolaryngology: Head & Neck Surgery. 2nd ed. New York, NY: McGraw-Hill; 2008:154.)

aIntensity relative to brain.

+++, moderate enhancement; ++++, maximal enhancement; IAC, internal auditory canal; MRI, magnetic resonance imaging.

Commonly used pneumonic for CPA is AMEN:

A: acoustic neuroma (~ 80% of the CPA tumor)

M: meningioma (~ 10% of the CPA tumor)

E: ependymoma (~ 5% of the CPA tumor)

N: neuroepithelial cyst (~ 5% arachnoid/epidermoid)

TREATMENT

A treatment plan must be created once a CPA tumor is diagnosed. Many factors must be considered when approaching these tumors. The patient’s age, overall health status, tumor size and location, degree of hearing loss, and other neurologic signs should be taken into account. The various available treatment options must be discussed with the patient; the final decision of treatment course must be decided between the patient and the physician.

At least three options should be considered in managing tumors in the posterior fossa: observation and serial imaging, stereotactic radiosurgery, or conventional surgery. Some of these options might be unavailable or unwise for certain tumor types or tumor size. Clearly, the patient who has a large tumor that produces brainstem compression or obstructive hydrocephalus should not be observed over time and serially imaged. These findings demand immediate attention.

Surgery can provide several benefits to the patient. Removal of the tumor allows for final pathologic diagnosis, might correct neurologic deficits, and might prevent further complications caused by continued tumor growth. These benefits can come at a price of new neurologic deficits, meningitis, infection, stroke, facial palsy, or even death. The patient’s underlying health status must be considered because these surgical procedures are often lengthy. Patients with a low overall health status might not tolerate such a procedure.

A relatively new (although >20 years’ experience) type of therapy involves the use of a directed, focus radiation beam to the tumor; this is called gamma knife radiation. Several different proprietary devices have been developed to destroy or at least prevent growth of these types of tumors. The experience with stereotactic radiotherapy is probably greatest with acoustic neuroma because it is the most common mass found in the CPA. Stereotactic radiotherapy has been found to be very effective at managing small- to medium-sized tumors (up to 3 cm). In these tumors, the complication rate for stereotactic radiotherapy is at least as low as that from conventional surgery; and with this type of therapy, a long hospital stay or recovery period is not required.

Using the currently recommended marginal dose of 12 to 13 Gray (Gy), long-term reported outcomes include not only tumor control rates of 92% to 100% but also functional preservation of the trigeminal and facial nerves, with values of 92% to 100% and 94% to 100%, respectively. Nonetheless, hearing preservation remains in the range of 32% to 81%. The disadvantage with stereotactic radiotherapy is the potential for continued growth, and this growth does occur in a significant number of patients. Unfortunately, surgery following stereotactic radiotherapy is technically more difficult, and surgical results are not as successful as from surgery alone.

Stereotactic radiotherapy has its limitations. It is not useful for certain tumor types (meningiomas and epidermoids). Stereotactic radiotherapy cannot provide pathologic specimens for study, and it should never be used when the pathologic diagnosis is in doubt.

CASE CORRELATION

• See also Case 35 (Facial Paralysis)

COMPREHENSION QUESTIONS

52.1 A 45-year-old painter is found to have ataxia. An MRI scan shows a tumor of the CPA. What is the most likely tumor in this location?

A. Epidermoid tumor

B. Paraganglioma

C. Meningioma

D. Acoustic neuroma

E. Lipoma

52.2 What is the best test to elucidate the etiology of unilateral sensorineural hearing loss?

A. Otoacoustic emissions

B. ABR

C. MRI of the internal auditory canals with gadolinium

D. Electronystagmography

E. Detailed physical examination

52.3 What is the most common cause of unilateral facial paralysis?

A. Idiopathic

B. Otitis media

C. Parotid malignancy

D. Acoustic neuroma

E. Lyme disease

ANSWERS

52.1 D. By far, the most common tumor in the CPA is the acoustic neuroma, comprising about 80% of the CPA neoplasms. This patient has the symptom of ataxia, which is less common than hearing loss; however, his occupation as a painter may cause a higher threshold for seeking medical attention for balance and coordination issues.

52. 2 C. Although ABR is used to evaluate unilateral sensorineural hearing loss, its limitation is a lack of specificity for diagnosis. Otoacoustic emissions can measure the degree of hearing loss, but it cannot shed light on a pathologic cause. Electronystagmography is a test that measures the vestibular ocular reflex. Detailed physical examination is an important prerequisite before any diagnostic tests are ordered. Only MRI with contrast enhancement can elucidate the cause of unilateral sensorineural hearing loss.

52.3 A. The most common form of facial paralysis is idiopathic. It is also called Bell palsy. Recent evidence suggests that the cause of Bell palsy is probably recrudescence of herpes simplex virus. Every patient should have a careful examination to rule out other causes of facial paralysis, such as those diagnoses listed. Where indicated, this examination might require an audiogram or MRI.

    CLINICAL PEARLS    

▶ Idiopathic facial paralysis (also called Bell palsy) is the most common cause of unilateral facial weakness. ▶ Bell palsy is a diagnosis of exclusion, and patients with facial paralysis require a careful otologic and cranial nerve examination. ▶ Patients who present with a complaint related to one cranial nerve require evaluation of all cranial nerves. ▶ Acoustic neuromas are the most common tumor of the CPA. ▶ Unilateral sensorineural hearing loss should be further evaluated by MRI with gadolinium contrast.

REFERENCES

Fan G, Curtin H. Imaging of the lateral skull base. In: Jackler R, Brackmann D, eds. Neurotology. 2nd ed. Philadelphia, PA: Elsevier; 2004:383-418. 

Hummel M, Krausgrill C, Perez J, Hagen R, Ernestus RI, Matthies C. Management of vestibular schwannoma: a pilot case series with postoperative ABR monitoring. Clin Neurol Neurosurg. 2016;143:139-143. 

Lo W, Hovsepian M. Imaging of the cerebellopontine angle. In: Jackler R, Brackmann D, eds. Neurotology. 2nd ed. Philadelphia, PA: Elsevier; 2005:349-382.

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