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Cystic acoustic neuroma
Journal of Clinical Neuroscience (2005) 12(3), 253–255 0967-5868/$ - see front matter ª 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2004.03.040
Clinical study
Cystic acoustic neuroma Su Wandong MD, Liu Meng MD, Li Xingang MD, Liu Yuguang MD, Zhu Shugan MD, Wang Lei MD, Wu Chengyuan MD Department of Neurosurgery, Qilu Hospital of Shandong University, Jinan, PR China
Summary To define the clinical characteristics of cystic acoustic neuroma, we retrospectively analyzed 22 patients with cystic acoustic neuroma and reviewed the literature with regard to clinical manifestation, imaging features, diagnosis, surgical procedures and prognosis. An acoustic neuroma was defined as cystic according to the following criteria: the presence hypodense/hypointense areas on CT or MRI, the identification of cystic elements at operation and histological verification. At the end of surgery the facial nerve was anatomically intact in 86.4% of cystic acoustic neuromas. Complete removal of the tumor was achieved in 18 cases (81.8%). We conclude that patients with cystic acoustic neuroma need prompt surgery with special attention paid to the preservation of the facial nerve. ª 2005 Elsevier Ltd. All rights reserved. Keywords: acoustic neuroma, neoplasm, cystic, neurosurgery
INTRODUCTION Acoustic neuroma is a relatively common intracranial tumor, and accounts for 8–10% of all primary intracranial tumors and 80% of cerebellopontine angle tumors. The tumor is generally composed of Antoni type A and B tissue histologically. Cystic areas are routinely observed in radiological studies of acoustic neuroma.1 This has long been held to be due to degenerative changes within the tumor or the coalescence of microcysts in Antoni type B tissue. However, recently it has been proposed that cystic tumors contain a predominance of the Antoni type B tissue, surrounded by a membrane-like structure composed of type A cells.2 The reported incidence of cyst formation in acoustic neuroma varies from 11.3%3 to 24%.1 Cystic acoustic neuroma has been associated with rapid tumor growth, short symptom duration, and with clinical facial nerve involvement.4 Twenty-two patients with cystic acoustic neuroma in a series of 289 cases of acoustic neuroma were treated in our hospital between January, 1996 and December, 2001. Diagnosis was confirmed at operation and by histopathology. We retrospectively analyzed these 22 patients and reviewed the literature with regard to clinical manifestation, imaging features, diagnosis, surgical procedures and prognosis.
images showed hyperintense cysts mixed within the isointense mass. Cysts varied in size and number but had similar signal characteristics between tumors. Tumor diameter ranged from 2.5 to 6.2 cm and it was more than 4.0 cm in 15 cases. All cases were operated via a sub-occipital retrosigmoid approach. An acoustic neuroma was deemed to be cystic according to the following criteria: the CT or MRI appearance as described above, operative identification of cystic elements and histological verification. In 59.1% of cystic acoustic neuromas there was adherence to the brainstem, in 45.5% to the tenth and eleventh cranial nerves and in 27.3% to the dura. At the end of surgery the facial nerve was anatomically intact in 86.4% of cystic acoustic neuromas. The post-operative facial nerve function was evaluated according to the House–Brackmann classification and the results are listed in Table 2. Complete removal was achieved in 18 cases (81.0%). Deliberate subtotal tumor removal was performed in 4 cases (18.2%) for various reasons, including facial nerve involvement, technical difficulty, risk of bleeding and brain stem adherence. There were no peri-operative deaths. At followup two years after surgery, no recurrence was found in the 18 cases with complete removal. In the 4 patients with subtotal removal there was residual tumor. Complications are listed in Table 3.
CLINICAL MATERIAL There were 12 males and 10 females, ranging in age from 14 to 69 years (mean 46 years). The duration of initial symptoms prior to definitive diagnosis was between 60 days and 10 years. Prior to surgery no patient had previous radiotherapy. The symptoms and signs of the 22 patients are listed in Table 1. All patients had plain and enhanced CT and MRI scans in our series. CT scan showed a mixed density mass in the cerebellopontine angle. These were isodense on the pre-contrast scan with hypodense areas. On administration of contrast, only the isodense portion of the tumor enhanced. Enlargement of the internal auditory canal was demonstrated in 14 cases. T1-weighted MRI showed isointense tumor with hypointense areas. T2-weighted Received 5 February 2004 Accepted 24 March 2004 Correspondence to: Dr. Su Wandong MD, Department of Neurosurgery, Qilu Hospital of Shandong University, Jinan, PR China. Tel.: +86 531 2169424; Fax: +86 531 6927544 E-mail: [email protected]
DISCUSSION Incidence and etiology In previous studies based only on neuroradiological images, the cystic tumors comprised 9.7%,5 11.3%,3 20.5%6 and 24%1 of all acoustic neuromas. Fundova et al.7 reported that the incidence of cystic acoustic neuroma was 5.7% based on appearance on CT or MRI with operative and immunohistological verification. This study included a large number of patients (773) and had strict criteria for classification of a tumor as cystic, and thus is probably more accurate. In our study, the incidence of cystic acoustic neuroma is 7.6%. The pathological mechanism of cyst development in acoustic neuroma is unclear thus far. Isolated or repeated intratumoral hemorrhage, hyaline, fatty, and mucinous degeneration and microcystic change have all been proposed as possible mechanisms of cyst formation. Antoni B tissue is characterized by a loose texture and is more commonly associated with cyst formation. Charabi et al.2,8 suggest that Antoni B tissue produces a myxomatous material in small cystic areas, which coalesce into larger 253
254 Wandong et al.
Table 1 Symptoms and signs of 22 patients presenting with cystic acoustic neuroma Symptoms and signs Hearing loss (incomplete) Headache Facial dysesthesia Tinnitus Ataxia Cranial nerve IX, X, XI dysfunction Hearing loss (complete) Papilledema Facial nerve palsy (HB grade 2) Facial nerve palsy (HB grade 4) Vertigo
Number of patients 20 19 18 15 14 8 6 5 4 2 1
enhancement is noted in 80% of the tumors after contrast administration. Enlargement of the internal auditory canal is common. CT cysternography is also helpful for anatomic delineation of acoustic neuroma. The differential diagnosis of this CT scan appearance is arachnoid cyst or epidermoid cyst. Due to the relatively lower resolution and bone artifact in the posterior fossa, it is difficult to distinguish cystic regions in a tumor from necrosis.
HB, House–Brackmann.
Table 2 Post-operative facial nerve function after 2 years using the House– Brackmann (HB) classification HB grade 2 3 4 5 6
Number of patients 5 8 4 2 3
Table 3 Complications of surgery for cystic acoustic neuroma in 22 patients Complication Cerebral edema Meningitis Postoperative hematoma CSF leak Death Total
Number of patients 3 1 0 0 0 4
cysts, which then compress the surrounding Antoni A tissue, thus creating membrane-like or capsular structure of Antoni type A tissue. Symptom onset and disease course A relatively rapid increase in tumor volume and acute evolution of symptoms of compression of surrounding structures are frequently observed with cystic acoustic neuroma. There has been much interest in the growth rate of acoustic neuroma with and without cyst formation. Kameyama et al.9 suggested that residual cystic acoustic neuroma was associated with rapid re-growth and required re-operation, as compared to residual acoustic neuroma without cyst formation. Fundova et al. reported that cystic acoustic neuroma was usually associated with a substantially shorter duration of symptoms and an increased risk of operative damage to the facial nerve compared with solid acoustic neuroma. Ki-67 immunostaining of cystic acoustic neuroma revealed that rapid volume increase was more likely to due to an increase in the cyst volume than to a high growth rate of tumor cells.2
Radiological appearance Cystic acoustic neuroma has characteristic CT findings with a mixed density mass in the cerebellopontine angle, which is isodense pre-contrast with hypodense areas. Marked heterogenous Journal of Clinical Neuroscience (2005) 12(3), 253–255
Fig. 1 The three subtypes of acoustic neuroma based on MRI appearance:10 (a) Type A – a large, single cystic region with a relatively small amount of peripheral solid tumor. (b) Type B – a cystic region within a largely solid tumor mass. (c) Type C – multicystic tumor.
ª 2005 Elsevier Ltd. All rights reserved.
Cystic acoustic neuroma
MRI is superior to CT for imaging of the posterior fossa and cerebellopontine angle, particularly for internal auditory canal lesions. T1-weighted MRI shows isointense tumor with hypointense areas. The T2-weighted image shows hyperintense cysts mixed with isointense tumor tissue. Cysts vary in size and number but have similar signal characteristics between tumors. The isointense solid regions of the tumor typically display marked and consistent early enhancement on T1-weighted images lasting 45–60 min after paramagnetic contrast administration. Arachnoid cysts and epidermoid cysts rarely show enhancement after contrast administration. Kameyama et al.10 divide cystic acoustic neuroma into three subtypes according to the MRI findings: (A) Large, single cystic region surrounded by a relatively small amount of peripheral tissue. (B) Single cystic region in a largely solid tumor. (C) Multicystic tumor. Type A and B tumors typically have a shorter clinical history than type C cystic acoustic neuroma. A cystic region in a largely solid tumor may be due to necrosis or hemorrhage within a solid tumor. In our study, 12 patients had type A tumors, 4 type B and 6 type C (Fig. 1(a)–(c)).
Treatment and prognosis The results of stereotactic radiosurgery for the treatment of cystic acoustic neuroma are relatively unsatisfactory.11 However, the results of surgical excision are much better. Fundova et al.7 reported that the outcome of the surgery for cystic acoustic neuroma was less favorable than that for solid acoustic neuroma. As cyst formation in acoustic neuroma is associated with rapid tumor growth, it may have a poor surgical outcome and higher morbidity.10 Cyst formation may predict a more intimate involvement of the neural tissue and a higher tendency to post-operative bleeding.12 In our study, we found that total resection with preservation of the facial nerve was more difficult in cystic acoustic neuroma than in solid tumors. This may be because the arachnoid plane is relatively difficult to preserve and the cranial nerves are displaced in a relatively uncertain position compared to solid tumors. Dissection of the facial nerve from the tumor is more difficult and the solid portion of the cystic acoustic neuroma appears more vascular than in solid tumors. Samii et al. reported that the rate of anatomic facial nerve preservation was reduced from 93% in solid tumors to 88% in cystic acoustic neuromas.13 In our group, the facial nerve
ª 2005 Elsevier Ltd. All rights reserved.
255
was anatomically intact at the end of surgery in 86.4% cases. Fundova et al. reported that cystic acoustic neuroma was more likely to be associated with hydrocephalus (27%) or intraoperative damage to the facial nerve than solid tumors. Charabi et al.4 reported that the growth rate of cystic acoustic neuroma is higher than that of solid tumor and that patients with cyst formation become more symptomatic in a shorter time, due to the expansion of cystic elements. Thus, cystic acoustic neuromas differ from solid tumors in their rapid growth, frequent involvement of the facial nerve and the unpredictability of their biological behavior. In conclusion, cystic acoustic neuroma has a worse surgical outcome compared to solid tumors. This should be taken into consideration when managing patients with cystic acoustic neuroma. These patients require prompt surgery due to the possibility of sudden expansion of the cystic elements. Particular attention should be given to preservation of the facial nerve.
REFERENCES 1. Wallace CJ, Fong TC, Auer RN. Cystic intracranial schwannoma. Can Assoc Radiol J 1993; 44: 453–459. 2. Charabi S, Klinken L, Tos M, Thomsen J. Histopathology and growth pattern of cystic acoustic neuromas. Laryngoscope 1994; 104: 1348–1352. 3. Tali ET, Yuh WT, Nguyen HD, et al. Cystic acoustic schwannomas: MR characteristics. AJNR Am J Neuroradiol 1993; 14: 1241–1247. 4. Charabi S, Tos M, Borgesen SE, Thomsen J. Cystic acoustic neuromas. Results of translabyrinthine surgery. Arch Otolaryngol Head Neck Surg 1994; 120: 1333–1338. 5. Kendall B, Symon L. Investigation of patients presenting with cerebellopontine angle syndromes. Neuroradiology 1977; 13: 65–84. 6. Robbins B, Marshall Jr WH. Computed tomography of acoustic neurinoma. Radiology 1978; 128: 367–370. 7. Fundova P, Charabi S, Tos M, Thomsen J. Cystic vestibular schwannoma: surgical outcome. J Laryngol Otol 2000; 114: 935–939. 8. Charabi S, Mantoni M, Tos M, Thomsen J. Cystic vestibular schwannomas: neuroimaging and growth rate. J Laryngol Otol 1994; 108: 375–379. 9. Kameyama S, Tanaka R, Honda Y, et al. The long-term growth rate of residual acoustic neurinomas. Acta Neurochir (Wien) 1994; 129: 127–130. 10. Kameyama S, Tanaka R, Kawaguchi T, et al. Cystic acoustic neurinomas: studies of 14 cases. Acta Neurochir (Wien) 1996; 138: 695–699. 11. Pendl G, Ganz JC, Kitz K, et al. Acoustic neurinomas with macrocysts treated with gamma knife radiosurgery. Stereotact Funct Neurosurg 1996; 66(Suppl 1): 103–111. 12. Matthies C, Samii M, Krebs S. Management of vestibular schwannomas (acoustic neuromas): radiological features in 202 cases – their value for diagnosis and their predictive importance. Neurosurgery 1997; 40: 469–481, Discussion 481–482. 13. Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): the facial nerve preservation and restitution of function. Neurosurgery 1997; 40: 684–694, Discussion 694–695.
Journal of Clinical Neuroscience (2005) 12(3), 253–255
Clinical study
Cystic acoustic neuroma Su Wandong MD, Liu Meng MD, Li Xingang MD, Liu Yuguang MD, Zhu Shugan MD, Wang Lei MD, Wu Chengyuan MD Department of Neurosurgery, Qilu Hospital of Shandong University, Jinan, PR China
Summary To define the clinical characteristics of cystic acoustic neuroma, we retrospectively analyzed 22 patients with cystic acoustic neuroma and reviewed the literature with regard to clinical manifestation, imaging features, diagnosis, surgical procedures and prognosis. An acoustic neuroma was defined as cystic according to the following criteria: the presence hypodense/hypointense areas on CT or MRI, the identification of cystic elements at operation and histological verification. At the end of surgery the facial nerve was anatomically intact in 86.4% of cystic acoustic neuromas. Complete removal of the tumor was achieved in 18 cases (81.8%). We conclude that patients with cystic acoustic neuroma need prompt surgery with special attention paid to the preservation of the facial nerve. ª 2005 Elsevier Ltd. All rights reserved. Keywords: acoustic neuroma, neoplasm, cystic, neurosurgery
INTRODUCTION Acoustic neuroma is a relatively common intracranial tumor, and accounts for 8–10% of all primary intracranial tumors and 80% of cerebellopontine angle tumors. The tumor is generally composed of Antoni type A and B tissue histologically. Cystic areas are routinely observed in radiological studies of acoustic neuroma.1 This has long been held to be due to degenerative changes within the tumor or the coalescence of microcysts in Antoni type B tissue. However, recently it has been proposed that cystic tumors contain a predominance of the Antoni type B tissue, surrounded by a membrane-like structure composed of type A cells.2 The reported incidence of cyst formation in acoustic neuroma varies from 11.3%3 to 24%.1 Cystic acoustic neuroma has been associated with rapid tumor growth, short symptom duration, and with clinical facial nerve involvement.4 Twenty-two patients with cystic acoustic neuroma in a series of 289 cases of acoustic neuroma were treated in our hospital between January, 1996 and December, 2001. Diagnosis was confirmed at operation and by histopathology. We retrospectively analyzed these 22 patients and reviewed the literature with regard to clinical manifestation, imaging features, diagnosis, surgical procedures and prognosis.
images showed hyperintense cysts mixed within the isointense mass. Cysts varied in size and number but had similar signal characteristics between tumors. Tumor diameter ranged from 2.5 to 6.2 cm and it was more than 4.0 cm in 15 cases. All cases were operated via a sub-occipital retrosigmoid approach. An acoustic neuroma was deemed to be cystic according to the following criteria: the CT or MRI appearance as described above, operative identification of cystic elements and histological verification. In 59.1% of cystic acoustic neuromas there was adherence to the brainstem, in 45.5% to the tenth and eleventh cranial nerves and in 27.3% to the dura. At the end of surgery the facial nerve was anatomically intact in 86.4% of cystic acoustic neuromas. The post-operative facial nerve function was evaluated according to the House–Brackmann classification and the results are listed in Table 2. Complete removal was achieved in 18 cases (81.0%). Deliberate subtotal tumor removal was performed in 4 cases (18.2%) for various reasons, including facial nerve involvement, technical difficulty, risk of bleeding and brain stem adherence. There were no peri-operative deaths. At followup two years after surgery, no recurrence was found in the 18 cases with complete removal. In the 4 patients with subtotal removal there was residual tumor. Complications are listed in Table 3.
CLINICAL MATERIAL There were 12 males and 10 females, ranging in age from 14 to 69 years (mean 46 years). The duration of initial symptoms prior to definitive diagnosis was between 60 days and 10 years. Prior to surgery no patient had previous radiotherapy. The symptoms and signs of the 22 patients are listed in Table 1. All patients had plain and enhanced CT and MRI scans in our series. CT scan showed a mixed density mass in the cerebellopontine angle. These were isodense on the pre-contrast scan with hypodense areas. On administration of contrast, only the isodense portion of the tumor enhanced. Enlargement of the internal auditory canal was demonstrated in 14 cases. T1-weighted MRI showed isointense tumor with hypointense areas. T2-weighted Received 5 February 2004 Accepted 24 March 2004 Correspondence to: Dr. Su Wandong MD, Department of Neurosurgery, Qilu Hospital of Shandong University, Jinan, PR China. Tel.: +86 531 2169424; Fax: +86 531 6927544 E-mail: [email protected]
DISCUSSION Incidence and etiology In previous studies based only on neuroradiological images, the cystic tumors comprised 9.7%,5 11.3%,3 20.5%6 and 24%1 of all acoustic neuromas. Fundova et al.7 reported that the incidence of cystic acoustic neuroma was 5.7% based on appearance on CT or MRI with operative and immunohistological verification. This study included a large number of patients (773) and had strict criteria for classification of a tumor as cystic, and thus is probably more accurate. In our study, the incidence of cystic acoustic neuroma is 7.6%. The pathological mechanism of cyst development in acoustic neuroma is unclear thus far. Isolated or repeated intratumoral hemorrhage, hyaline, fatty, and mucinous degeneration and microcystic change have all been proposed as possible mechanisms of cyst formation. Antoni B tissue is characterized by a loose texture and is more commonly associated with cyst formation. Charabi et al.2,8 suggest that Antoni B tissue produces a myxomatous material in small cystic areas, which coalesce into larger 253
254 Wandong et al.
Table 1 Symptoms and signs of 22 patients presenting with cystic acoustic neuroma Symptoms and signs Hearing loss (incomplete) Headache Facial dysesthesia Tinnitus Ataxia Cranial nerve IX, X, XI dysfunction Hearing loss (complete) Papilledema Facial nerve palsy (HB grade 2) Facial nerve palsy (HB grade 4) Vertigo
Number of patients 20 19 18 15 14 8 6 5 4 2 1
enhancement is noted in 80% of the tumors after contrast administration. Enlargement of the internal auditory canal is common. CT cysternography is also helpful for anatomic delineation of acoustic neuroma. The differential diagnosis of this CT scan appearance is arachnoid cyst or epidermoid cyst. Due to the relatively lower resolution and bone artifact in the posterior fossa, it is difficult to distinguish cystic regions in a tumor from necrosis.
HB, House–Brackmann.
Table 2 Post-operative facial nerve function after 2 years using the House– Brackmann (HB) classification HB grade 2 3 4 5 6
Number of patients 5 8 4 2 3
Table 3 Complications of surgery for cystic acoustic neuroma in 22 patients Complication Cerebral edema Meningitis Postoperative hematoma CSF leak Death Total
Number of patients 3 1 0 0 0 4
cysts, which then compress the surrounding Antoni A tissue, thus creating membrane-like or capsular structure of Antoni type A tissue. Symptom onset and disease course A relatively rapid increase in tumor volume and acute evolution of symptoms of compression of surrounding structures are frequently observed with cystic acoustic neuroma. There has been much interest in the growth rate of acoustic neuroma with and without cyst formation. Kameyama et al.9 suggested that residual cystic acoustic neuroma was associated with rapid re-growth and required re-operation, as compared to residual acoustic neuroma without cyst formation. Fundova et al. reported that cystic acoustic neuroma was usually associated with a substantially shorter duration of symptoms and an increased risk of operative damage to the facial nerve compared with solid acoustic neuroma. Ki-67 immunostaining of cystic acoustic neuroma revealed that rapid volume increase was more likely to due to an increase in the cyst volume than to a high growth rate of tumor cells.2
Radiological appearance Cystic acoustic neuroma has characteristic CT findings with a mixed density mass in the cerebellopontine angle, which is isodense pre-contrast with hypodense areas. Marked heterogenous Journal of Clinical Neuroscience (2005) 12(3), 253–255
Fig. 1 The three subtypes of acoustic neuroma based on MRI appearance:10 (a) Type A – a large, single cystic region with a relatively small amount of peripheral solid tumor. (b) Type B – a cystic region within a largely solid tumor mass. (c) Type C – multicystic tumor.
ª 2005 Elsevier Ltd. All rights reserved.
Cystic acoustic neuroma
MRI is superior to CT for imaging of the posterior fossa and cerebellopontine angle, particularly for internal auditory canal lesions. T1-weighted MRI shows isointense tumor with hypointense areas. The T2-weighted image shows hyperintense cysts mixed with isointense tumor tissue. Cysts vary in size and number but have similar signal characteristics between tumors. The isointense solid regions of the tumor typically display marked and consistent early enhancement on T1-weighted images lasting 45–60 min after paramagnetic contrast administration. Arachnoid cysts and epidermoid cysts rarely show enhancement after contrast administration. Kameyama et al.10 divide cystic acoustic neuroma into three subtypes according to the MRI findings: (A) Large, single cystic region surrounded by a relatively small amount of peripheral tissue. (B) Single cystic region in a largely solid tumor. (C) Multicystic tumor. Type A and B tumors typically have a shorter clinical history than type C cystic acoustic neuroma. A cystic region in a largely solid tumor may be due to necrosis or hemorrhage within a solid tumor. In our study, 12 patients had type A tumors, 4 type B and 6 type C (Fig. 1(a)–(c)).
Treatment and prognosis The results of stereotactic radiosurgery for the treatment of cystic acoustic neuroma are relatively unsatisfactory.11 However, the results of surgical excision are much better. Fundova et al.7 reported that the outcome of the surgery for cystic acoustic neuroma was less favorable than that for solid acoustic neuroma. As cyst formation in acoustic neuroma is associated with rapid tumor growth, it may have a poor surgical outcome and higher morbidity.10 Cyst formation may predict a more intimate involvement of the neural tissue and a higher tendency to post-operative bleeding.12 In our study, we found that total resection with preservation of the facial nerve was more difficult in cystic acoustic neuroma than in solid tumors. This may be because the arachnoid plane is relatively difficult to preserve and the cranial nerves are displaced in a relatively uncertain position compared to solid tumors. Dissection of the facial nerve from the tumor is more difficult and the solid portion of the cystic acoustic neuroma appears more vascular than in solid tumors. Samii et al. reported that the rate of anatomic facial nerve preservation was reduced from 93% in solid tumors to 88% in cystic acoustic neuromas.13 In our group, the facial nerve
ª 2005 Elsevier Ltd. All rights reserved.
255
was anatomically intact at the end of surgery in 86.4% cases. Fundova et al. reported that cystic acoustic neuroma was more likely to be associated with hydrocephalus (27%) or intraoperative damage to the facial nerve than solid tumors. Charabi et al.4 reported that the growth rate of cystic acoustic neuroma is higher than that of solid tumor and that patients with cyst formation become more symptomatic in a shorter time, due to the expansion of cystic elements. Thus, cystic acoustic neuromas differ from solid tumors in their rapid growth, frequent involvement of the facial nerve and the unpredictability of their biological behavior. In conclusion, cystic acoustic neuroma has a worse surgical outcome compared to solid tumors. This should be taken into consideration when managing patients with cystic acoustic neuroma. These patients require prompt surgery due to the possibility of sudden expansion of the cystic elements. Particular attention should be given to preservation of the facial nerve.
REFERENCES 1. Wallace CJ, Fong TC, Auer RN. Cystic intracranial schwannoma. Can Assoc Radiol J 1993; 44: 453–459. 2. Charabi S, Klinken L, Tos M, Thomsen J. Histopathology and growth pattern of cystic acoustic neuromas. Laryngoscope 1994; 104: 1348–1352. 3. Tali ET, Yuh WT, Nguyen HD, et al. Cystic acoustic schwannomas: MR characteristics. AJNR Am J Neuroradiol 1993; 14: 1241–1247. 4. Charabi S, Tos M, Borgesen SE, Thomsen J. Cystic acoustic neuromas. Results of translabyrinthine surgery. Arch Otolaryngol Head Neck Surg 1994; 120: 1333–1338. 5. Kendall B, Symon L. Investigation of patients presenting with cerebellopontine angle syndromes. Neuroradiology 1977; 13: 65–84. 6. Robbins B, Marshall Jr WH. Computed tomography of acoustic neurinoma. Radiology 1978; 128: 367–370. 7. Fundova P, Charabi S, Tos M, Thomsen J. Cystic vestibular schwannoma: surgical outcome. J Laryngol Otol 2000; 114: 935–939. 8. Charabi S, Mantoni M, Tos M, Thomsen J. Cystic vestibular schwannomas: neuroimaging and growth rate. J Laryngol Otol 1994; 108: 375–379. 9. Kameyama S, Tanaka R, Honda Y, et al. The long-term growth rate of residual acoustic neurinomas. Acta Neurochir (Wien) 1994; 129: 127–130. 10. Kameyama S, Tanaka R, Kawaguchi T, et al. Cystic acoustic neurinomas: studies of 14 cases. Acta Neurochir (Wien) 1996; 138: 695–699. 11. Pendl G, Ganz JC, Kitz K, et al. Acoustic neurinomas with macrocysts treated with gamma knife radiosurgery. Stereotact Funct Neurosurg 1996; 66(Suppl 1): 103–111. 12. Matthies C, Samii M, Krebs S. Management of vestibular schwannomas (acoustic neuromas): radiological features in 202 cases – their value for diagnosis and their predictive importance. Neurosurgery 1997; 40: 469–481, Discussion 481–482. 13. Samii M, Matthies C. Management of 1000 vestibular schwannomas (acoustic neuromas): the facial nerve preservation and restitution of function. Neurosurgery 1997; 40: 684–694, Discussion 694–695.
Journal of Clinical Neuroscience (2005) 12(3), 253–255