What Is an Acoustic Neuroma?

Acoustic neuroma refers to a tumor that originates from the auditory nerve sheath. It is a benign tumor. The exact designation is an acoustic nerve sheath tumor. % To 95%. More common in adults, the peak is 30-50 years old, rare under 20 years old, children with a single auditory neuroma are very rare, so far, all cases are reported. No significant gender difference. The incidence of left and right is similar, with occasional bilaterality. Clinically, pontine cerebellar horn syndrome and increased intracranial pressure are the main manifestations.

Basic Information

nickname

Auditory schwannoma

English name

acoustic neuroma

Visiting department

neurosurgery

Multiple groups

30-50 years old

Common causes

Inner ear canal segment

Common symptoms

Pontine cerebellar horn syndrome, increased intracranial pressure sign

Causes of acoustic neuroma

Acoustic neuroma mostly originates from the inner ear canal of the phrenic nerve. It can also originate at the beginning of the inner sheath of the inner ear canal or at the base of the inner ear canal. Rarely, acoustic neuroma originates from the auditory nerve, mostly from the superior vestibular nerve, followed by the inferior vestibule. Nerves are generally unilateral, with fewer occurring simultaneously on both sides.

Clinical manifestations of acoustic neuroma

Early ear symptoms

When the tumor volume was small, tinnitus, hearing loss, and dizziness appeared on one side, and a few patients developed deafness after a long time. Tinnitus can be accompanied by paroxysmal vertigo or nausea and vomiting.

2. Mid-term facial symptoms

When the tumor continued to grow, the ipsilateral facial nerve and trigeminal nerve were compressed, facial muscle twitching and lacrimal gland secretion decreased, or mild peripheral facial paralysis occurred. Trigeminal nerve damage is manifested by facial numbness, pain, hypotensiveness, weakened corneal reflexes, poor temporal and chewing muscle strength, or muscle atrophy.

3. Advanced cerebellar pontine angle syndrome and posterior cranial nerve symptoms

When the tumor is large, it compresses the brainstem, cerebellum, and posterior cranial nerves, causing cross hemiplegia and hemiplegia, cerebellar ataxia, unstable gait, difficulty in pronunciation, hoarseness, difficulty swallowing, eating cough, etc. . Occurrence of cerebrospinal fluid circulation obstruction is headache, vomiting, vision loss, optic nipple edema, or secondary optic nerve atrophy.

Auditory neuroma

A typical acoustic neuroma has the above-mentioned clinical manifestations of progressive aggravation, and can be clearly diagnosed with the help of imaging and nerve function tests.

Radiological examination

(1) X-ray film of the skull shows plain enlargement of the inner ear canal, bone erosion, or bone resorption.

(2) CT and MRI scans CT showed that tumors were of equal density or low density, and a few showed high density images. The tumors are mostly round or irregular, located in the mouth area of the inner auditory canal. The MRIT ₁ weighted image shows a slightly lower or equal signal, and the T ₂ weighted image shows a high signal. The fourth ventricle is compressed and deformed, and the brainstem and cerebellum are deformed and displaced. After injection of contrast agent, the parenchymal part of the tumor was significantly strengthened, and the cystic area was not strengthened.

2. Neuro-otology examination

Because patients only have tinnitus and deafness in the early stage, they often visit the otology clinic. Hearing tests and vestibular nerve function tests are commonly used.

(1) Hearing examination There are 4 methods of hearing examination to distinguish whether the hearing impairment is a disorder from the conduction system, the cochlea or the auditory nerve. Hearing test type 1 is normal or middle ear disease; type II is cochlear hearing loss; types III and IV Type is the threshold test for auditory neuropathy tone decay. If the tone subsides more than 30dB, it is an auditory nerve disorder, and the score of the short enhanced sensitivity test is 60% to 100% for cochlear disease. The binaural alternation volume balance test is a cochlear disease, and no supplement is a middle ear or auditory neuropathy.

(2) Vestibular nerve function test Most of the auditory neuroma originated from the vestibular part of the auditory nerve. Early use of hot and cold water tests can almost always find the lesion of the vestibular nerve on the diseased side, the reaction completely disappeared or partially disappeared. This is a common method for diagnosing acoustic neuromas. However, because the fibers from the vestibular nucleus cross the pontine to the contralateral side and are located in the shallow part, they are susceptible to compression by large pontine cerebellar horn tumors, and about 10% of patients on the healthy side can have impaired vestibular function.

Acoustic Neuroma Treatment

Surgical treatment

Acoustic neuroma is the first choice for surgical treatment, which can be completely removed and completely cured. If surgery remains, consider a supplemental gamma knife treatment.

2. Stereotactic radiation therapy

In recent years, with the development of microneurosurgery and intraoperative neuroelectrophysiological monitoring technology, the surgical resection rate and facial nerve retention rate of acoustic neuromas have greatly improved, but the trauma and surgery caused to patients by surgery cannot be ignored. After various complications. With the development of imaging technologies such as CT and MRI, the positioning and qualitative diagnosis of acoustic neuromas have become more accurate, which has provided a guarantee for the application of stereotactic radioneurology in the treatment of acoustic neuromas, and has gradually become a micro-surgery following microsurgery. Beyond another treatment. At present, the main treatment equipment of stereotactic radiation therapy are X knife, gamma knife, proton knife, etc. The X knife is low in cost and convenient to use, but it has the disadvantages of mechanical loss to the positioning target offset; gamma knife positioning is accurate without mechanical loss. Targets are offset, but there are disadvantages such as expensive equipment and long initial preparation. Therefore, when selecting a treatment plan, it is necessary to make a personalized choice based on the patient's condition and the hospital's own situation. At present, in clinical studies of stereotactic radiation therapy for acoustic neuromas, the long-term follow-up tumor growth control rate is about 90%, the vestibular nerve preservation rate is 38% to 71%, and the facial nerve preservation rate is to (according to House-Brack-man Classification) is 90% to 100%. The tumor control rate is high, the complications are few, and it has certain advantages in retaining hearing and reducing facial nerve injury. However, stereotactic radiotherapy also has its shortcomings, such as the inaccurate radiotherapy effect of large tumors. Therefore, it is necessary to strictly grasp the indications of radiotherapy.