| It is estimated that incidence of acoustic neuromas (AN) is around 6%-9% of all intracranial tumors and 80%-90% of tumors in cerebellopontine angle which ranks the fourth following meningioma, hypophysoma and neurospongioma. It arises from the vestibular nerve and is caused by an overproliferation of schwann cells. It is one kind of benign tumors with malignant clinical performances. Complete excision is the first choice, meanwhile it is also important to avoid complications such as facial and cochlear nerve dysfunction after operation.At present, there are some limitations for selecting and administering the therapeutic regimens of AN. So it is necessary to get thoroughly understand about the characteristic of this tumor. In this study, surgical practices of AN were summarized up to 23 years. Furthermore, how to preserve the facial nerve and how to monitor the hearing changes to eventually keep normal hearing were also explored. Additionally, the results of study on the relationship among bionomics, MRI signal, histologic characteristics and cell proliferation could be used to predict the growth of tumor and provide a more reasonable therapeutically plan to improve patients' living quality.Part One: clinical analysis of surgical treatment for acoustic neuromasWe retrospectively analyzed 125 cases of acoustic neuroma undergoing surgical treatment in a span from 1983.3 to 2006.3. Among them, there were 111 cases with complete patient's information, 93 cases with complete follow-up information six months after operation, and 65 cases with complete information of one year after operation.In 111 cases, there were 87 cases with complete excision ( 87/111, 78.38%),while 12 cases with partial excision or internal-cyst excision. In addition, there were 36 cases in TL surgical approach, 10 cases in MF surgical approach and 65 cases in RS surgical approach. In this study, all cases survived the surgical procedure. Serious surgical complications include leakage of cerebrospinal fluid (14.4%), intracranial hematoma(6.3%), post group cranial nerve dysfunction(4.5%), meningitis(3.6%), limbs handicap(3.6%), balance disturbance(1.8%), hemiplegia and aphasia(0.9%)and extradural hematoma(0.9%). These results indicated that the safety of surgical treatments for acoustic neuroma has been improved greatly.The objective of present study was to evaluate the effectiveness of intraoperative facial nerve monitoring and auditory nerve monitoring during vestibular schwannoma resection. The results of anatomical preservation of facial nerve with intraoperative facial nerve monitoring (IFNM) was better than that of no intraoperative facial nerve monitoring (NIFNM) (95.24% vs 76.7%, P<0.05). And the difference of the facial nerve function after 6 months was significant (House-Brackmann Grade I or II) (77.78% vs 56.67%, P<0.05, respectively).Twelve cases of AN were resected by RS. Continuous hearing monitoring of ABR and ECochG were performed during operation. Hearing was preserved in 2 cases, and the tumor size was smaller than 2cm. Both of them ranked class A hearing preoperation and postoperation. During continuous hearing monitoring, the waves I and Illcould be evoked, whereas wave V appeared in one case at the end of the operation. Ten cases had total hearing loss after operation, among which the waves I and III could be evoked, wave V disappeared in one case. But it had complication of intracranial hematoma, epidural hematoma and extradural hematoma in the first day after surgery, and resulted in total hearing loss. There were waves I (AP) in 7 of 10 cases. The AP amplitudes decreased significantly in 5 cases or dropped to zero when operation neared the internal auditory canal (IAC). After operation, the AP amplitudes were recovered 50~60 percent or completely. In one case, although the cochlear nerve was cut down, the AP could still be recorded after the tumor resection. In another case, however, theAP amplitude dropped to zero while entry zone of cochlea nerve was pulled and no wave could be observed from then on. Two had no significant waves after anesthesia. One of them showed lower amplitude of AP after partial resection. The others didn't show any waves all the time. In order to reduce irreversible hearing damage significantly, intra-operative hearing monitoring by combination of ABR and ECochG during operation would be performed in the future to promote hearing outcome. Drilling of IAC and removal of tumor at the lateral end of the IAC were considered as the most critical step for achieving hearing preservation. If waves I , III and V or waves I and III could be evoked, the hearing would be survived after tumor resection. The AP was not sensitive to detect auditory damages but susceptible to auditory ischemia and vasospasm. The hearing would not be survived if only the AP could be evoked after tumor resection. The postoperative hearing could not be predicted by results of AP.In this series, 5 cases were administered by endoscope during operation, with its merits, surgeon can observe the relations among tumor, nerves and vessels more easily. So it is helpful to keep important structures safe during removal of tumor. But the disadvantages would have to be noticed when using endoscope: First, surgeon could only operate with one hand;second, hemorrhage could block image of endoscope;finally, image of endoscope was two-dimensions.This study showed that microsurgical technique had made zero mortality of acoustic neuromas opreation come true. Preservations of hearing, facial nerve and cochlear nerve were improved obviously. Monitoring technique of the facial nerve should be one of the most important methods to preserve the facial nerve function. It was possible to preserve hearing by monitoring the cochlear nerve and more research were needed to identify other fluencing factors.Part Two: bionomical studies of acoustic neuromasThere are 53 cases with complete clinical information in this study. Histological characteristics and MRI images were analyzed. With immunohistochemistry method, TGF- P i expression was confirmed and theproliferation index of tumor cell was calculated. Using data above-mentioned, the relationship among tumor proliferation, MRI characteristics of acoustic neuroma, histological representation, size of tumor, clinical proliferation index of tumor, tumor proliferation activity were analyzed. The significance of TGF- P 1 expression was also discussed. Based on transmission electron microscope, bionomics of acoustic neuroma on ultra structural level could be understood. Result: In MRI, homogeneous signals were mostly Antoni A type, heterogeneous signals and cystic degeneration were mostly Antoni B type and (or) mixed type(P<0.05).Based on tumor diameter, the tumor sizes were listed as cystis degeneration, heterogeneous and homogeneous respectively. The tumor with heterogeneous signal and cystis degeneration had hemorrhage or abundant of Antoni B type tissue, which grow faster potentially and is dangerous. Cell proliferation labeling index LI (Ki-67) was unrelated to tumor size, but it was related to LI (PCNA) and clinical growth rate. The expression of TGF-P i of acoustic neuroma in Antoni A type was much higher than Antoni B type and mixed type (PO.05), but LI (Ki-67) had positive correlation with TGF-3 i(r=0.35963, P<0.05 ). So TGF- P i had something to do with biological behavior of acoustic neuroma. Cystis degeneration was one special pattern of acoustic neuroma. Tumor size enlargement was due to enlargement of volume of the cysit but not fast proliferation of parenchyma cell;cystis degeneration often occurred in large-size tumor, which mostly resulted from thrombogenesis, hemorrhage, necrosis and exudation. Clinically, they tended to grow quickly, so the tumor needed to be observed carefully. Under Electron microscope, type Antoni B presented increasing blood vessel and organelle in organelle, which hints to intensive metabolic activity and provided evidences on molecular level that type Antoni B would be grow quickly and could have cystis degeneration. Conclusion: In MRI, homogeneous signals were mostly Antoni A type;heterogeneous signals and cystis degeneration were mostly Antoni B type and (or) mixed type. The tumors of heterogeneous signal and cystis degeneration growfaster with potential dangerousness. Cell proliferation-labeling index LI (Ki-67) and LI (PCNA) were related to clinical growth rates? which reflected proliferation activities of tumor cells. TGF- 3 i may participate in the biological behavior of acoustic neuroma. Cystis degeneration was one special pattern of acoustic neuroma, and enlargement was due to volume of the cysit but unrelated to fast proliferation of parenchyma cell. |
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