Acoustic schwannoma

Introduction to auditory nerve sheath The sphincter sheath originates from the auditory nerve sheath and is a typical schwannomas, accounting for 7.79% to 10.64% of intracranial tumors, accounting for 93.1% of intracranial schwannomas, and accounting for 72.2% of cerebellopontine angle tumors. In the 30 to 60 years old, those under the age of 20 are rare, and women are slightly more than men. Most of the tumors occur in the vestibular segment of the auditory nerve, and a few occur in the cochlea of the nerve. As the tumor grows larger, the outer side of the pons and the anterior cerebellum are compressed, which is filled in the cerebellar pons, and most of the tumor is unilateral. A few are bilateral, such as with neurofibromatosis, the opposite is true. The tumor is a benign lesion, and even if it recurs many times, it does not undergo malignant transformation and metastasis. If it can be removed, it can often obtain a permanent cure. basic knowledge Sickness ratio: 1%-2% Susceptible people: no specific population Mode of infection: non-infectious Complications: cerebrospinal fluid leakage hydrocephalus

The cause of acoustic nerve sheath tumor

Cause (64%):

Molecular genetic studies have found that the occurrence of schwannomas (single or bilateral) is related to the inactivation of NF2 gene, a tumor suppressor gene, located in the long arm 1 region 2 and 2 subbands of chromosome 22 (22q12.2). ), the NF1 gene is also a tumor suppressor gene, located 19q11.2.

Pathogenesis (25%):

Auditory schwannomas cause cerebellar pons syndrome, the symptoms can be light and heavy, which is mainly related to the initial site of the tumor, growth rate, development direction, tumor size, blood supply and cystic changes, etc. The vestibular part is damaged first, so in the early stage, there is loss or decrease of one side vestibular function and stimulation or partial paralysis of the cochlear nerve. As the tumor grows, the anterior pole can touch the sensory root of the trigeminal nerve. Pain in the same side, facial sensation diminished, corneal reflex is slow or loss, and the tip of the tongue and the side of the tongue feels diminished. If the movement root of the trigeminal nerve is also affected, the ipsilateral masticatory muscle weakness may occur, and the mandibular jaw is biased toward the affected side, the masticatory muscle. And the atrophy of the diaphragm.

Auditory nerve sheath prevention

Primary prevention is to reduce or eliminate the carcinogenic effects of various carcinogenic factors on the human body and reduce the incidence. If you should pay attention to participate in physical exercise, change your own low mood, maintain strong energy, thus improve the body's immune function and disease resistance; pay attention to diet, drinking water hygiene, prevent cancer from entering the mouth; do not eat mold and corruption, burnt Food and smoked, grilled, marinated, soaked food, or not drinking for a long time, no smoking, no alcohol, scientific diet, eat more fresh vegetables, fruits and nutritious foods, develop good Health habits. At the same time, attention should be paid to protecting the environment, avoiding and reducing pollution to the atmosphere, diet and drinking water, preventing physical, chemical and parasitic, viral and other carcinogenic factors from invading the human body and effectively preventing cancer.

Secondary prevention is an effective means of early detection, early diagnosis and early treatment to reduce the death of cancer patients. In addition to strengthening physical exercise in daily life, you should also pay attention to some physical changes and regular physical examination. Such as taking chest radiographs, bronchoscopy can find early lung cancer; B-mode ultrasound scan, alpha-fetoprotein determination, can reveal liver cancer; routine vaginal cytology examination, early detection of cervical cancer; esophageal pull net examination, fiber esophagoscopy, Gastroscope, colonoscopy, early detection of esophageal cancer, gastric cancer, colon cancer. Therefore, once you find that your body has cancer, you must go to the oncology hospital to diagnose and treat, establish confidence in the fight against cancer, and actively cooperate, cancer can be cured.

Tertiary prevention is to prevent cancer recurrence and metastasis and prevent complications and sequelae when treating cancer. At present, oncology hospitals have the advantage of a comprehensive treatment, and have different treatment methods for different tumor diseases. Such as surgical removal of tumors, chemotherapy, radiotherapy, Chinese medicine, immunity and other treatments. I believe that as long as you pay attention to learning and master the common and basic knowledge of cancer prevention and treatment, everyone can capture the signs and manifestations of certain cancers as soon as possible so that they can seek medical treatment in time and assist doctors in timely diagnosis and timely treatment.

Auditory schwannoma complications Complications, cerebrospinal fluid, hydrocephalus

Hearing impairment

Although various techniques and monitoring methods have been applied to improve the preservation rate of hearing, since the hearing nerve is more sensitive to intraoperative damage than facial nerve, it is easy to cause damage during surgery, affecting hearing, the size of the tumor volume, whether the tumor invades the internal auditory canal and Whether or not the internal auditory can be enlarged can affect the hearing after surgery.

2. Facial nerve damage

Because of the slow growth of acoustic nerve sheath tumors, until the demyelination of facial nerve fibers exceeds 50% or axonal degeneration occurs, clinical signs of obvious dysfunction will occur. Therefore, facial nerve function damage represents severe compression, indicating that recovery is incomplete. The size of the tumor, whether the facial nerve adheres to the tumor, and whether the tumor grows into the facial nerve can affect the prognosis, sharp separation during surgery, avoiding traction and electrocoagulation, and minimizing the damage of the facial nerve.

3. Cerebrospinal fluid leakage

It is a common complication of sphincter sphincter surgery. It is reported that the incidence rate is 16%. Most of the 1 week after operation, cerebrospinal fluid leakage has the potential to induce meningitis. Cerebrospinal fluid leakage occurs due to subarachnoid space and shale bone or There is traffic or fistula between the mastoids.

4. Hydrocephalus

Edema in the midbrain, pons or medulla may cause hydrocephalus, usually accompanied by obstruction of the ventricles or subarachnoid space, hematoma in the parenchyma, posterior fossa hematoma or hemorrhage into the fourth ventricle can also induce hydrocephalus .

5. Meningitis

Meningitis occurs in 2% to 10% of patients undergoing suboccipital acoustic neuroma surgery. It is common in aseptic meningitis, mainly caused by blood, bone powder or other surgical substances contaminating the subarachnoid space. Bacterial meninges Inflammation is usually associated with cerebrospinal fluid leakage.

6. Damage to other cranial nerves

When the suboccipital approach is used to remove acoustic neuroma, all cranial nerves (V~VII) in the posterior fossa may be temporarily or permanently damaged by vascular, inflammatory or mechanical manipulation, microsurgical techniques, especially It is to avoid traction, attraction and thermal damage to reduce damage to these nerves.

Symptoms of auditory schwannomas Common symptoms Tinnitus hearing loss nausea hearing loss sensory disturbance dizziness ear vestibular function impaired intracranial pressure increased deafness visual impairment

The duration of the sphincter sphincter is longer, and the symptoms can last from several months to several years. Generally, it lasts for 3 to 5 years. The main symptoms of most patients are the symptoms of the sphincter itself, including dizziness, tinnitus and hearing. Decline, these three can occur simultaneously or both at the same time, tinnitus is a high pitch, like a humming or whistle sound, and is continuous, often accompanied by hearing loss, deafness is more important, according to the relevant data report deafness exists in In 85.2% to 100% of cases, tinnitus is only present in 63% to 66.9% of cases. Because the patient has mild symptoms of dizziness and is not accompanied by nausea and vomiting, it is often not noticed by patients and doctors. It is an objective sign that can be detected. If the unilateral deafness is not accompanied by tinnitus, it is often not noticeable to the patient. Occasionally, hearing loss is observed when listening to the phone, or until the complete deafness or other related neurological symptoms are caused. The length of the disease reflects the growth rate of the tumor, the location of the tumor, and whether there is a cystic change. The incidence of clinical symptoms is related to the degree of tumor development. Some authors report The incidence of dizziness was linearly and negatively correlated with the extent of tumor expansion. The smaller the tumor, the higher the incidence of dizziness. The incidence of dizziness was 86% in T1, 65% to 66% in T2 and T3, and 51 in T4. %, the duration of dizziness symptoms is linearly and negatively correlated with the size of the tumor. The larger the auditory nerve sheath, the shorter the duration of dizziness symptoms.

1. The first symptom, the intracranial segment of the nerve can be divided into two parts, the inner part and the outer part. The inner part of the inner auditory canal is called the outer part, and the inner part from the brain stem to the inner ear hole is called the inner part. The junction is roughly the medullary myelin and Schwann cell myelin demarcation zone. Since most of the tumor occurs in the lateral part, the first symptom of most patients is progressive unilateral hearing loss accompanied by tinnitus and dizziness, accounting for about 70%. And this symptom lasts for a long time, usually 3 to 5 years. When the tumor originates from the proximal end of the auditory nerve, because the medial tumor has no bone wall limitation, it will not affect the auditory nerve in the early stage. The first symptom is not hearing impairment, but Headache, nausea and vomiting, visual impairment are the first symptoms. A few elderly patients may have mental changes, manifested as apathetic, indifferent, and unresponsive to surrounding conditions, which may be related to cerebral arteriosclerosis and increased intracranial pressure in the elderly.

2. Secondary symptoms, physical signs of auditory schwannomas are more complicated, the clinical symptoms are not exactly the same, the symptoms can be light and heavy, which is mainly related to the tumor starting site, growth rate, development direction, tumor size, blood supply and Whether it is cystic change and many other factors.

(1) Hearing performance: The most common and typical manifestation of auditory schwannomas is unilateral or more severe sensorineural deafness, also known as sensorineural deafness, which is generally considered to be associated with progressive unilateral hearing loss. Tinnitus is the earliest and most prominent complaint of sphincter tumors. This type of hearing impairment has the following characteristics:

1 The treble rate hearing was first affected, then gradually extended to the mid-bass, causing the slope to treble hearing impairment curve, and finally generally declined.

2 language screening rate is lower than normal, and often not commensurate with bass hearing, that is, pure tone hearing is still in the normal range or only mildly reduced, and the language screening rate is significantly reduced.

3 The air conduction is still larger than the bone conduction, but both are shortened, and the ratio of bone conduction/air conduction is unchanged.

4 Hearing loss is progressive, but 10% of patients show sudden changes or sudden changes in the process of hearing loss.

The occurrence of sudden deafness may be caused by cochlear ischemia caused by tumor compression in the internal auditory canal. Therefore, patients with sudden deafness should also be alert to the possibility of hearing schwannomas.

(2) vestibular symptoms: The function of the vestibular nerve is to regulate the balance of the body, including the head, eyeball, body, limbs, and regulate the body's response to various accelerations. The most common symptoms of vestibular nerve damage are dizziness and nystagmus. Dizziness is a feeling that the patient feels the external environment or is rotating or moving. Although the incidence of vertigo as the first symptom is higher, the actual vertigo is significantly less than the first symptom. Some authors report the vestibular nerve. Symptoms accounted for only 10% of the patients, and in the history of the follow-up, 65% of cases had vestibular nerve involvement, and some occurred a few years ago. Dizziness often occurs at rest but some patients are changing positions such as bending over. Induced or aggravated when sitting or turning the head, some patients may be relieved by taking sedative drugs. Dizziness may be accompanied by nausea and vomiting. The performance is sometimes similar to Meniere's disease. Foreign studies report that 30% have true vertigo, of which Many patients with long-term acute labyrinthine attacks, lasting several days or longer, were diagnosed with labyrinthitis or vestibular neuronitis, and nystagmus was mostly Flatness or horizontal rotation, the direction of slow phase of nystagmus is consistent with the direction of limb deflection. When the brain stem is severely pushed, it can damage the vestibular central nystagmus in the vestibular center. The duration of nystagmus is long, the rhythm is large, and the nystagmus The direction of the slow phase can be inconsistent with the deviation of the limb.

(3) Trigeminal Symptoms: Trigeminal dysfunction is the third most common cranial nerve symptom. The trigeminal nerve is located on the ventrolateral side of the pons in the middle of the cerebral palsy. It consists of a large sensory root and a small moving root. Under the attachment edge of the curtain, walk forward and outward, cross the rock bone and enter the Meckel cavity, and connect with the half moon joint. When the auditory nerve sheath grows forward and upward, it can affect the trigeminal nerve and squeeze the trigeminal nerve on the upper pole of the tumor. Symptoms of trigeminal nerve damage occur between the pons and the midbrain. A group of 1000 patients with auditory schwannomas have 9% of symptoms of trigeminal involvement. The symptoms of trigeminal nerves are as follows:

1 Most patients showed facial numbness as the main symptom. The clinical examination showed that the facial numbness of the patients was significantly higher than that of the subjective sensation, indicating that some patients had already felt symptoms of diminished, but did not attract attention.

Two patients presented with trigeminal neuralgia.

3 may be accompanied by masticatory muscle atrophy. In general, the damage of the trigeminal nerve branch is less, and it appears later. It may be that the motor nerve fiber is more resistant to compression than the sensory fiber. Deviated to the affected side, the diaphragmatic and masseter muscles of the diseased side contracted weakly and atrophied.

4 Isolated trigeminal nerves are less affected, most of them are affected by 2 or 3, and the duration of trigeminal involvement is linearly positively correlated with tumor size. The average duration is 1.3 years, if trigeminal symptoms It is mainly caused by 1, 2 branches, and the corneal reflex is reduced or disappeared, but it is often not noticed by the patient. For one side of the cornea with reflex or disappearance, and one side of the auditory nerve symptoms and signs, it can be regarded as the performance of early auditory schwannomas. Bilateral corneal reflex damage is associated with increased intracranial pressure and tumor compression of the brain stem. Patients often have more lesions on the lesion side.

(4) facial nerve performance: patients with acoustic schwannomas rarely have symptoms and signs of facial paralysis in the early stage. Foreign studies report that 6% of patients with auditory nerve sheath tumor have facial nerve symptoms, facial nerve damage signs appear later, and the degree is also light, possibly motor nerve The fiber has a large tolerance to external stress. Therefore, the long-term facial paralysis caused by acoustic nerve sheath tumor is rare and mostly atypical, because 50% of the nerve fibers of the facial nerve can maintain normal functions, and should be taken seriously when examining the body. Careful, in order to avoid omission, there are still reports of sphincter tumors with recurrent hemifacial tendons, and there are reports of sphincter tumors with only facial paralysis and misdiagnosed as Bell facial paralysis.

(5) Symptoms of increased intracranial pressure: increased intracranial pressure is one of the common clinical features of auditory schwannomas. The morning and evening symptoms of increased intracranial pressure are related to tumor size, growth rate, growth site and other factors. The larger the tumor volume, the more obvious the symptoms of increased intracranial pressure, but the medial tumor, because the tumor is close to the midline, although the tumor volume is not large, the early cerebrospinal fluid circulation is affected, resulting in obstructive hydrocephalus, the symptoms of increased intracranial pressure can be In the early stages of the disease and more prominent, the cause of increased intracranial pressure is:

1 During the process of tumor ingrowth, the medullary medulla is displaced, and the lower part of the aqueduct and the IV ventricle are compressed.

2 Some tumors grow in the direction of the cerebellum, and some of the tumors protrude into the curtain to compress the aqueduct.

3 The posterior cranial fossa and the lower part of the ring pool were occluded by tumor compression and affected cerebrospinal fluid circulation.

4 During the tumor growth process, due to the folding of the arachnoid membrane, arachnoid cysts are formed around the tumor, occupying a certain volume in the cranial cavity.

5 Tumors cause large holes in the occipital bone, causing a sharp increase in intracranial pressure.

Symptoms of increased intracranial pressure are most common with headaches. Severe cases are accompanied by nausea and vomiting. Visual acuity often occurs. Headache symptoms are mostly located in the frontal occipital or bilateral ankles. The unilateral occipital pain seems to be localized. Some patients are still unclear. The location of the pain, the cause of the headache, in addition to the increased intracranial pressure caused by the stimulation and involvement of the meningeal blood vessels and nerves, and other causes, so headache can occur early, headache can be persistent pain, but also sustainable Pain is aggravated, often headache is more severe in the morning, intermittent period can be normal, patients with simple headache can last for more than a few years, such as headache and other symptoms at the same time, it means that the course of disease is shorter, increased intracranial pressure makes the optic nerve Pressure, ocular venous return obstruction, resulting in optic disc edema, severe intracranial pressure can occur retinal hemorrhage, increased intracranial pressure for a long time, can cause secondary atrophy of the optic nerve, the fundus examination, the visual disc becomes light, The edge is unclear, the patient usually has vision loss or black Mongolian, and even some patients are blind, usually affected on both sides, individual patients due to intracranial pressure increase Progression is rapid, and sudden coma, bilateral pupil diminution, later dilated, and soon respiratory disorder, manifested as slow breathing, irregular or apnea, such as occipital macroporous syndrome, so some authors believe that intracranial pressure The presence of increased syndrome indicates that the patient has entered the metaphase or advanced stage. For patients with medial-type auditory schwannomas, due to the lack of cerebellar pons, the symptoms and signs of the cerebral pons, only the symptoms of early intracranial hypertension, and the posterior fossa tumors such as cerebellar hemisphere tumors. And the midline tumor is difficult to identify, causing diagnostic difficulties, therefore, the neurological examination and neuroradiology should be used to determine the diagnosis.

Examination of auditory nerve sheath tumor

1. Neurological examination

Because the patient has only tinnitus and deafness in the early stage, he often visits the ear department. Commonly used are hearing tests and vestibular nerve function tests.

(1) Hearing examination: There are 4 kinds of hearing examination methods, which can distinguish hearing impairment from conduction system, cochlear or auditory nerve obstacle, Bekesy hearing test, type I is normal or middle ear disease, type II is cochlear hearing loss, Type III, IV is auditory neuropathy, sound decay threshold test. If the tone subsides more than 30dB for auditory nerve disorder, the short-enhanced sensitivity test score is 60%-100% for cochlear lesions, and the binaural alternating volume balance test has supplementary phenomenon for cochlear lesions. The middle ear or auditory neuropathy with no supplementation.

(2) vestibular neurological examination: auditory schwannomas originate from the vestibular part of the auditory nerve. Early detection of vestibular nerve dysfunction can be found in both cold and hot water tests. The reaction completely disappears or partially disappears. This is the diagnosis of auditory nerve sheath tumor. The common method, but because the fiber from the vestibular nucleus is located in the shallower part of the cerebral bridge crossing to the contralateral side, it is easy to be oppressed by the large cerebellar pons tumor, and about 10% of the vestibular function of the healthy side can be damaged.

2. Neuroradiological diagnosis

(1) X-ray film: The main change is the expansion of the internal auditory canal caused by bone resorption, and the abnormality of the rock bone fault slice: the width of the inner auditory canal is more than 2 mm larger than the contralateral side, and the posterior wall of the internal auditory canal is more than 3 mm. The contour of the concave edge of the medial end of the internal auditory canal is obscured or blurred, and the horizontal sputum is displaced below the midpoint of the height of the internal auditory canal.

(2) cerebral angiography: the characteristics of the lesions seen are: the basilar artery is close to the slope, the central vein of the cerebellum is moved backward, the bridge, the anterior cerebral vein is close to the slope, and the venous point is moved backward. The anterior inferior cerebellar artery is displaced by the mass from the internal auditory canal. The basilar artery and bridge, the anterior and middle cerebral veins are all moved backward, and the basilar artery can be moved to the opposite side, and the tumor is stained.

(3) CT and MRI examination: The current gold standard for the diagnosis of sphingomyelia is Gd-DTDA-enhanced MRI, especially when the tumor is small (<1cm) or in the internal auditory canal, CT scan is negative and highly suspected of tumor, GD-DTPA enhanced MRI should be performed.

CT and MRI have complementary effects. For example, when CT is found to have enlarged internal auditory canal, enhanced CT can detect tumor, and the degree of gasification of the tibia and the high jugular bulb and posterior semicircular canal are estimated for the middle cranial fossa approach. The distance between the bottom and the bottom is helpful. If the patient has had CT and the tumor is large, MRI can provide a range of brain stem compression, whether the IV ventricle is unobstructed, whether hydrocephalus is present, or suspected auditory schwannomas or CT examination. When it is difficult to determine, the full sequence of MRI can make a differential diagnosis, but also pay attention to the possible false positive of Gd-DTPA, which is related to inflammation of the internal auditory canal or arachnoiditis. Any small, near-bottom enhanced lesion should be An MRI review was conducted after June to assess its growth.

3. Brainstem auditory evoked potential or brainstem electrical response audiometry

For a non-invasive electrophysiological examination, positive for V wave delay or loss, more than 95% of acoustic schwannomas have this performance, has been widely used in the early diagnosis of this tumor.

Diagnosis and differentiation of auditory schwannomas

diagnosis

1. Typical schwannomas have the following characteristics

(1) Early symptoms are mostly caused by vestibular nerve and cochlear nerve damage of the auditory nerve. It is characterized by dizziness, progressive unilateral hearing loss accompanied by tinnitus, and the first symptoms are mostly tinnitus and deafness. Tinnitus tends to last for a short time, and deafness develops. Slow, sustainable for years or decades, most are not noticed by patients.

(2) tumor adjacent to the cranial nerve damage performance, generally with trigeminal nerve and facial nerve damage more common, manifested as peripheral peripheral facial paralysis, or suffering from lateral numbness, masseter muscle weakness or atrophy.

(3) There are symptoms such as cerebellar ataxia or side cone sign in which the walking is unstable and the movement is uncoordinated.

(4) headache, nausea and vomiting, optic disc edema and other symptoms of increased intracranial pressure and dysphagia, drinking water cough, hoarseness and other groups of brain damage.

According to the patient's typical disease evolution process and specific performance, the diagnosis is not difficult, but the key to the problem lies in the early diagnosis. It is best to be in the "ear department" stage of the vestibular nerve and cochlear nerve damage or the tumor is limited to the inner auditory canal. Can make an accurate diagnosis, in order to improve the total resection rate of the tumor, reduce the risk of surgery, and maximize the possible preservation of the facial nerve and auditory nerve function.

2. Patients with early symptoms should consider the possibility of hearing schwannomas.

(1) intermittent or progressively worsening tinnitus.

(2) Hearing is progressively declining or sudden deafness.

(3) A temporary unsteady feeling occurs when dizziness or body position changes.

(4) Intermittent tingling in the deep part of the external auditory canal or deep in the mastoid. In addition to tinnitus, the patients in the "ear department" stage often lack other neurological symptoms and signs, and most of the patients go to the ear clinic, and the medical staff should improve. Be alert.

Therefore, for patients with hearing loss after middle and old years, if there is no other reason, such as trauma, otitis media, etc., should consider whether there is the possibility of hearing schwannomas, hearing and vestibular function tests, brain stem evoked potentials, general radiography Etc., if necessary, brain CT and magnetic resonance examination should be performed to further confirm the diagnosis.

Although 75% to 80% of cases have typical cerebellar pons, but some cases do not have typical clinical manifestations, so the diagnosis should be based on the initial site of the tumor, the direction of development and other different clinical features. Analysis, the inner type of auditory nerve sheath tumor early VIII cranial neuropathy may not be obvious or atypical, and the symptoms of increased intracranial pressure, one side of the pyramidal tract sign and cerebellar ataxia appear earlier, the course of disease tends to progress faster, on the contrary, Lateral auditory schwannomas often present with deafness and tinnitus as the first symptom. This symptom can last for a long time, followed by the evolution of typical auditory schwannoma disease, the difference between intraductal acoustic schwannomas and medial and lateral auditory schwannomas. It is often the symptoms of vestibular and cochlear nerve damage, and facial nerve symptoms appear earlier, other clinical symptoms are relatively rare, clinical analysis should be combined with the results of auxiliary examinations, so that the correct diagnosis can be made early.

Differential diagnosis

Any tumor located in the cerebellopontine angle of the pons may be confused with acoustic neuroma, but most cases have the MRI identification characteristics. The acoustic nerve sheath tumor accounts for 90% of the cerebellopontine angle tumor, followed by meningioma, epidermoid tumor, arachnoid cyst. Lipoma, facial nerve sheath tumor and metastatic tumor.

Meningiomas account for 10% to 15% of cerebellopontine angle lesions. CT and MRI have similar density and signal intensity. Their morphology and location are often different from those of auditory nerve sheath tumors. Meningioma is expressed behind rock bones. For a fixed mass, the axis is not heard inside, the internal auditory is not often invaded by the tumor, and there are bone hyperplasia in 15% to 25% of cases. In addition, 25% to 35% of cases have Intratumoral calcification, 50% to 70% of the D1 weighted MRI of Gd-DTPA has a dural tail sign, it is important to focus on the shape of the tumor rather than a certain individual characteristics, calcification and dural tail sign in the acoustic nerve sheath tumor Rare performance.

Epidermoid tumors account for 10% to 20% of cerebellopontine angle lesions, showing a non-enhancing lesion and low signal on T1-weighted images, higher than cerebrospinal fluid signal, high signal on T2-weighted images, arachnoid cyst often Simultaneously with auditory schwannomas, but also an isolated pathology, this cyst has a signal consistent with cerebrospinal fluid compared with epithelioid tumors, arachnoid cysts are uniform, and epithelioid tumors are consistently thin and heterogeneous Sexual features, followed by arachnoid cysts that displace blood vessels, and epidermoid tumors penetrate into the fissures and are surrounded by neurovascular structures.

Lipomas are rare and are reported to be isolated lesions in the internal auditory canal, or invading the inner auditory canal and cerebellar pons, with a typical high signal on T1 weighted effects, which is difficult to enhance due to their original high signal. In the evaluation, on the T2-weighted image, it may be equal intensity or low intensity, and the fat suppression sequence is introduced in the MRI, so that the disease becomes a low signal, and it is easy to diagnose the lipoma preoperatively.

Metastatic tumors are rare, but cerebral edema in their immediate vicinity should cause high suspicion.

Schwann cell tumors of other cranial nerves in the posterior fossa also appear in the cerebellopontine angle of the cerebral pons, but their origins are often different. Trigeminal schwannomas are the most common, often extending to the middle cranial fossa and the posterior cranial fossa with dumbbell shape, facial nerve sheath tumor Often in the geniculate ganglia, but when it occurs in the inner auditory canal or cerebral cerebral horn, it is difficult to distinguish from auditory schwannomas.

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