Auditory neuroma is the most common benign tumor of the pontocerebellar horn and is traditionally treated by craniotomy. Since the beginning of the use of gamma knife as a treatment for auditory neuroma in 1968, good results have been achieved. At present, for auditory neuroma of about 3 cm, gamma knife and microsurgery have become an alternate treatment method.
I. Patient selection
1.The maximum diameter of the tumor is about 3 cm. Those with partial cystic changes can be relaxed appropriately.
2, older and systemic conditions can not withstand general anesthesia craniotomy, gamma knife treatment can be preferred.
3.Postoperative residual tumor, postoperative recurrence and no obvious brainstem compression.
4, those who want to maintain the function of facial and auditory nerve.
5. Microsurgery is recommended for those with severe trigeminal neuralgia.
II. Preoperative preparation (omitted)
Positioning options
1.MR+CT (bone window position).
2.MR.
3.CT (bone window position): pay attention to avoid artifacts when installing the cephalic frame.
IV. Principles of measurement plan
1.Choose different size collimators according to the size of the lesion.
2.Generally use 50% isodose curve to cover the tumor, and do not advocate the use of too high isodose curve.
3.The number of collimators and the size of weights should be used reasonably in order to obtain a satisfactory measurement plan and maximize the radiobiological effect.
4.Eventually produce a satisfactory radiation foci (three-dimensional image) similar to the volume of the lesion.
5.Peripheral dose 10, 5 – 15Gy (reference dose).
6.The internal auditory canal is a bony canal with no compensatory space, and a slightly lower dose is recommended in the internal auditory canal.
V. Postoperative treatment
1, after the end of the gamma knife with 20% mannitol 250ml + dexamethasone 2, 5mg IV once to reduce the acute radiation reaction.
2, prophylactic antimicrobial.
3.Neurotrophic agents.
4.Allopathic treatment.
Sixth, follow up
1.Follow up the patient once every six months for two years. Perform detailed neurological examination, especially facial, auditory and trigeminal nerve scores. And do imaging examination. (It is recommended to do cranial MR scan + enhancement).
2.If the tumor shrinks or remains the same size after two years, follow up with imaging examination after one year.
3.If the tumor still shrinks or remains the same size after three years, follow up in two, four, eight or sixteen years intervals.
4.Many patients (especially those with partial cystic change of tumor), after gamma knife treatment
About 6 months after gamma knife treatment, imaging examination shows that the center of the tumor is weakened, and the volume can be significantly increased is a normal pathological change process, as long as the patient’s symptoms are not significantly aggravated, not accompanied by increased intracranial pressure. As long as the patient’s symptoms are not significantly aggravated and there is no intracranial pressure increase, it is not necessary to consider “tumor enlargement, treatment is ineffective, and surgical treatment is performed”. Generally, the line to judge whether the treatment is effective is 2 years after gamma knife treatment.
VII. Complications
1, facial nerve: postoperative facial nerve paralysis of varying degrees generally occurs in the treatment
3-6 months after the treatment period. Once early treatment (hormones, neurotrophic agents, physiotherapy, etc., most of them can recover to varying degrees), the actual incidence of permanent facial paralysis is about 2%.
2.Auditory nerve: hearing may decrease 10-20 decibels after surgery, hearing retention rate depends on preoperative hearing level, hearing preservation is about 51%.
3, trigeminal nerve: postoperative facial sensory loss and numbness about 6% or so, usually with mild symptoms, and generally the motor branch of the trigeminal nerve is not involved.
4.Tinnitus: difficult problem
5.Cerebellar ataxia symptoms
6, traffic hydrocephalus: about 5% of patients can occur traffic hydrocephalus, mainly related to the characteristics of the disease cerebrospinal fluid protein increase, absorption disorders. Ventriculoperitoneal shunt can be performed.