acoustic neuroma
Introduction
Introduction to acoustic neuroma Acoustic neuroma is a benign schwannomas of the vestibular (eighth nerve) originating from Schwann cells. Acoustic neuroma accounts for about 7% of intracranial tumors. Hearing loss, tinnitus, dizziness and instability are early symptoms. Other symptoms appear when the tumor grows up and presses the brain. Early diagnosis relies on MRI and audiological examinations, including brainstem evoked potentials. Small tumors are removed by microsurgery to avoid damage to the facial nerve; large tumors require extensive surgical resection. Acoustic neuroma is a benign tumor. It has a good early diagnosis and early treatment. Tinnitus is the first symptom of acoustic neuroma. As long as the tinnitus is like the sound of autumn, you should seek medical advice immediately. Head computer tomography or magnetic resonance imaging can confirm the diagnosis. Tumor diameter > 3cm or existing intracranial hypertension, surgical resection of the tumor is the only way out; if the tumor diameter <3cm, can be considered -knife or X-knife treatment, but the cost is slightly higher, so far, no food has been found A certain food or drug can make a tumor shrink or disappear. basic knowledge The proportion of illness: 0.003% Susceptible people: no specific population Mode of infection: non-infectious Complications: dizziness, deafness, headache, facial paralysis, edema
Cause
The cause of acoustic neuroma
Causes
The cause is unclear, and the possible causes are: genetic factors, physical and chemical factors, and biological factors.
The acoustic neuroma originates from the inner ear canal of the VIII cranial nerve, and can also originate from the beginning of the inner ear canal nerve sheath or the inner ear canal. The acoustic neuroma rarely comes from the auditory nerve, but mostly from the vestibular superior nerve, followed by the vestibular The nerves are generally unilateral, and there are fewer occurrences on both sides at the same time. The appearance of the tumors is gray-red, different in size and shape, and the quality of the bottom is different from that of the capsules. There are membranes on the surface of the tumor. The tumor cells under the microscope are mostly spindle-shaped, long-core rod-shaped, arranged in a fence or a spiral shape. The cytoplasm is like a longitudinal fibrous shape. It contains cells such as rough endoplasmic reticulum. Protrusion, staggered in the intercellular space, and collagen fibers and Ross body coexist, and some tumor cells are polygonal, clustered, unclear, composed of different size and shape of the network, there are mucus-containing micro-cells Two types of cells can coexist, only one of them is the main one, the tumor grows slowly, and the speed can be different in different periods. If the development is too fast, the center can be liquefied, and the blood vessels of the tumor itself are not much distributed. No nerves Walk through.
Pathogenesis
The symptoms of cerebellar pons syndrome can be mild or severe, which is mainly related to the initial site of tumor, growth rate, development direction, tumor size, blood supply and cystic changes. At the beginning of the tumor, the vestibular part is the first to be damaged. 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, its anterior pole can touch the sensory root of the trigeminal nerve and cause pain in the same side of the face, facial sensation is reduced, corneal reflex is slow or lost, and the tip of the tongue and the side of the tongue feel reduced. If the movement root of the trigeminal nerve is also affected, the ipsilateral masticatory muscle weakness may occur, the mouth and jaw may be biased toward the affected side, and the masticatory muscles and diaphragm muscles may be atrophied.
In pathology, most of the tumors originate from the vestibular part of the auditory nerve, 3/4 originates from the upper vestibular nerve, and a few are from the cochlear part. The vestibular nerve inner part (outer part) is about 10 mm long, the pons cerebral horn part (inside part) is 15 mm, and the total length is about 25 mm. There is a boundary band between the glial myelin sheath and the Schwann cell myelin sheath. In the inner ear hole area. Tumors often occur in the internal auditory canal because they originate from Schwann cells. About 3/4 of the tumors occur in the lateral part, and only 1/4 occur in the medial part. As the tumor grows and grows, the tumor can cause the internal auditory canal to expand, and the cerebral pons is filled into the cerebral pons. Most of the tumors are unilateral, and a few are bilateral; if they are accompanied by neurofibromatosis, the opposite is true.
The probability of occurrence on both sides varies from one report to another. In general, the incidence of the left and right sides is almost equal. The acoustic schwannomas have a complete envelope, and the surface is mostly smooth, sometimes slightly nodular, and its shape and size depend on the growth of the tumor. Generally, after the clinical diagnosis is established, the volume has mostly exceeded 2.5 cm in diameter. Large tumors can occupy the entire posterior cranial fossa and move up through the canopy to the edge of the occipital foramen. The medial side can reach the opposite side of the pons. The tumor always resides in the subarachnoid space in the cranial cavity. Therefore, the surface always has a thickened arachnoid covering, and a certain amount of cerebrospinal fluid is wrapped like arachnoid cyst. The parenchymal part of the tumor is grayish yellow to grayish red, and the texture is firm and brittle. There are often cysts of different sizes in the tumor tissue, which contain light yellow transparent cysts and sometimes fibrin clots. The tumor and the cerebellum are closely adhered to each other, but generally do not invade the cerebellar parenchyma. Most of the tumors protrude into the inner auditory canal, causing the opening to expand. The meninges are often tightly attached to the tumor. The facial nerve tube is closely attached to the inner side of the tumor due to more adhesions, and often cannot be visually distinguished. This makes surgery to preserve facial nerves a problem, so microsurgery is particularly important.
The main blood supply of the tumor comes from the anterior inferior cerebellar artery. This blood vessel separates into the tumor capsule near the tumor and divides into several small branches into the tumor tissue. Other branches of the pons artery with the basilar artery and the posterior inferior cerebellar artery of the superior cerebellum to the tumor. The small blood vessels associated with small sphincter tumors are the anterior inferior cerebellar artery. The surface in contact with the cerebellum also receives arterial blood supply from the surface of the cerebellum. The venous return mainly enters the superior sinus auditory nerve through the rock vein.
Prevention
Acoustic neuroma prevention
Acoustic neuroma is a benign tumor. It has a good early diagnosis and early treatment. Tinnitus is the first symptom of acoustic neuroma. As long as the tinnitus is like the sound of autumn, you should seek medical advice immediately. Head computer tomography or magnetic resonance imaging can confirm the diagnosis. Tumor diameter > 3cm or existing intracranial hypertension, surgical resection of the tumor is the only way out; if the tumor diameter <3cm, can be considered -knife or X-knife treatment, but the cost is slightly higher, so far, no food has been found A certain food or drug can make a tumor shrink or disappear.
Complication
Acoustic neuroma complications Complications, dizziness, deafness, headache, facial paralysis, edema
Patients with hearing impairment after middle and lower years, if there is no other reason, such as trauma, otitis media, etc., should be thought to be a sphincter tumor, should go to the hospital as soon as possible.
The acoustic neuroma is located in the cerebral horn of the cerebellar pons, and the course of the disease is long. The first symptoms are almost all obstacles of the auditory nerve itself, including dizziness, dizziness, unilateral tinnitus and deafness. The tinnitus is high-pitched, like humming or whistling, and is continuous, often With hearing loss, (ushing describes the procedure for the appearance of symptoms in detail:
1 cochlear and vestibular symptoms are dizziness, dizziness, tinnitus, deafness.
2 occipital headache accompanied by discomfort in the large occipital region of the diseased side.
3 cerebellar sympathetic movement disorders, movements are not coordinated.
4 adjacent cranial nerve damage symptoms, such as side pain, facial convulsions, facial sensation diminished, peripheral facial paralysis.
5 symptoms of increased intracranial pressure, such as optic nerve head edema, increased headache, vomiting, double vision and so on.
Symptom
Acoustic neuroma symptoms Common symptoms Paroxysmal dizziness, cough and reflex, papilledema, ear vestibular hearing loss, tremor
(1) Early symptoms:
1 Tinnitus: One side, the pitch is different, the progressiveness is increased, and it starts at the same time as hearing loss, but it may also be the only symptom in the early stage.
2 Hearing loss: One-sided progressive deafness, often expressed in the early days when talking to people, smelling their voices and not knowing what they are, and gradually developing into full-fledged.
3 vertigo: a small number of transient vertigo, accompanied by pressure in the ear, nausea, vomiting, such as membrane lost water symptoms, but most of the performance is unstable; due to slow tumor development, vestibular gradual compensation can cause The vertigo disappeared.
4 In the deep side of the affected ear or in the mastoid pain, the posterior wall of the external auditory canal is numb.
(2) Symptoms of tumor invasion or primary in the posterior cranial fossa:
1 trigeminal nerve is affected by the branch; the same side is numb.
2 can appear on the same side of the peripheral facial paralysis.
3 In the advanced stage, if the tumor oppresses the cerebellum, there will be unclear vocalization and movement disorders.
4 headache: at the beginning of the occipital and top, in the late stage due to increased intracranial pressure, the full headache; can be accompanied by visual impairment and brain conduction beam involvement symptoms.
Examine
Audition of acoustic neuroma
Neurological examinations are often seen in the ear because of the earliest tinnitus and deafness in the patient. Commonly used are hearing tests and vestibular nerve function tests.
Hearing test
There are four types of hearing tests that distinguish hearing impairment from hearing, cochlear or auditory nerve impairment tests, type I is normal or middle ear disease; type II is cochlear hearing loss; and type III IV is auditory neuropathy tone decline threshold test. If the pitch subsides more than 30dB for auditory nerve disorders, the short-enhanced sensitivity test score is 60% to 100% for cochlear lesions, and the binaural alternating volume balance test has a cochlear lesion with an additive phenomenon, and the middle ear or auditory neuropathy without supplementation.
Vestibular nerve function test
The acoustic neuroma originated from the vestibular part of the auditory nerve. In the early stage, almost all the symptoms of vestibular nerve function damage and complete disappearance or partial disappearance were found in the hot and cold water test. This is a common method of diagnosing acoustic neuroma. However, since the fibers from the vestibular nucleus cross the pons to the contralateral side, about 10% of the vestibular function in the shallower part of the oppressive side of the large cerebellar pons tumor can be damaged.
Neuroradiological diagnosis
(1) X-ray film:
The main change is the index of bone mass absorption caused by the enlargement of the internal auditory canal. The width of the inner auditory canal is more than 2mm larger than the contralateral side; the posterior wall of the internal auditory canal is more than 3mm; the inner auditory canal is concave. The quality profile disappears or is ambiguous; the sputum level shifts below the midpoint of the height of the inner auditory canal.
(2) cerebral angiography:
The characteristics of the lesions seen are: the basilar artery is close to the slope; the anterior cerebellar central vein is moved backward; the bridge and the mid-brain vein are close to the slope; the venous point is moved backward; when the lesion is large, the anterior cerebellar artery is also seen from inside. The lumps of the auditory canal, the basilar artery and the bridge, the anterior and middle cerebral veins all move backward; the basilar artery can move to the opposite side; the tumor is stained.
(3) CT and MRI examinations:
The current diagnostic criteria for sphingomylin is Gd-DTDA-enhanced MRI, especially when the tumor is small (<1 cm) or within the internal auditory canal, and the CT scan is negative and highly suspected of tumor presence should be GD-DTPA-enhanced MRI. CT and MRI have complementary effects. For example, when CT is found to have enlarged internal auditory canal, enhanced CT can be used to estimate the degree of gasification of the tibia and the high jugular bulb and posterior semicircular canal for estimating the middle cranial fossa approach. The distance at the bottom helps. If the patient has had CT and the tumor is large, MRI can provide a range of brain stem compression. IV ventricle is open to hydrocephalus, whether the presence of it is difficult to determine for suspected auditory schwannomas or CT examination, the full sequence of MRI can be done Differential diagnosis. But also pay attention to the possible false positives of Gd-DTPA, which is related to inflammation or arachnoiditis in the internal auditory canal; any small enhancement lesions near the bottom should be reviewed by MRI after June to assess their growth.
Brainstem auditory evoked potential
Brainstem auditory evoked potential or brainstem electrical response hearing test is 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 this Early diagnosis of the tumor.
Diagnosis
Diagnosis of acoustic neuroma
Diagnostic points
Early
Ear Symptoms Tumor volume is small, one side of tinnitus, hearing loss and dizziness appear, and a few patients have deafness after a little longer. Tinnitus can be accompanied by paroxysmal vertigo or nausea or vomiting.
Medium term
Facial Symptoms When the tumor continues to increase, the ipsilateral facial nerve and the trigeminal nerve are compressed, and facial muscle twitching and lacrimal gland secretion are reduced, or mild peripheral facial paralysis is present. Trigeminal nerve damage manifests as facial numbness, pain, decreased tactile sensation, decreased corneal reflex, poor diaphragm muscle and masticatory muscles, or muscle atrophy.
Late
Cerebellar cerebral horn syndrome and posterior cranial nerve symptoms, when the tumor volume is large, oppressing the brain stem, cerebellum and posterior cranial nerve, causing cross-biased and partial sensory disturbance, cerebellar ataxia, gait instability, Difficulty in pronunciation, hoarseness, difficulty swallowing, eating cough, etc. Cerebrospinal fluid circulatory obstruction may have headache, vomiting, vision loss, papilledema or secondary optic atrophy.
Differential diagnosis
Acoustic neuroma should be differentiated from facial neuroma: facial neuromas are rare, and can occur anywhere in the facial nerve from the brainstem to the neuro-muscle junction, occurring in the cerebellopontine angle (CPA) and the internal auditory canal (IAC). The clinical manifestations resemble acoustic neuromas. The clinical features of facial neuroma depend on the location and extent of the lesion. Although there are reports of cases of acute facial paralysis and fluctuating facial paralysis, the most common clinical symptoms are still progressive facial paralysis, sensorineural neuropathy. Deafness, dizziness, and tinnitus may be clinical symptoms of tumors located in CPA and IAC, in addition to 2/3 dysfunction of the tongue, facial convulsions, dry eyes, dry mouth and other symptoms.
When facial neuroma grows in CPA or IAC, facial nerve palsy is uncommon. MRI and CT cannot identify the surface located in CPA or IA C. Acoustic neuroma, some symptoms of acoustic neuroma, facial palsy or paralysis, facial paralysis and taste Obstruction, etc., should consider the possibility of facial neuroma.
