preservação da função do nervo facial schwanoma...

Preservação da função do nervo facial

e da audição em cirurgias de

Schwanoma Vestibular

Luiz Cláudio Modesto Pereira

Doutorando FCS - UNB

Neurocirurgião HBDF

Neuroma do acústico / Schwanoma

Vestibular

Considerações gerais:

O “neuroma do acústico” é um tumor benigno originado das células de Schwann em torno no nervo vestibular.

È o mais freqüente schwanoma intracraniano e mais comum tumor do APC

Em 1991, o NIH (National Institutes of Health), após conferencia de consenso sobre o neuroma do acústico concluiu que a denominação preferida seria Schwanoma Vestibular. Ainda assim o longo tempo de uso do termo prévio o consagrou,

ainda hoje não tendo sido totalmente abandonado...

Os neuromas do acústico ocorrem em 2 grupos distintos: Ocorrência esporádica unilateral: sem historia familiar e sem

associação a outros tumores ou anormalidades do SNC.

Ocorrência Bilateral, usualmente familiar, na facomatose “neurofibromatose tipo 2”. Nestes casos outros tumores intracranianos ou espinhais podem ocorrer.

R. G. Ojemann Youmans - Neurological Surgery 4ª/e

Neuroma do acústico / Schwanoma

Vestibular Considerações gerais:

A perda auditiva é o sinal clinico inicial mais comum Usualmente a redução é lenta mas podendo ser

aguda e ter evolução flutuante.

Um dos primeiros sinais é a dificuldade de compreender palavras ao telefone...

Tinnitus, tonturas, vertigens, sensação de “peso ou entupimento no ouvido” podem se seguir

A medida que o tumor alarga este começa a comprimir o nervo trigêmeo podendo causar dormência em face.

Em pacientes com tumores largos podem ainda ocorrer Cefaléia, diplopia, as vezes HIC

Instabilidade de marcha, ataxia

Rouquidão e dificuldade de deglutição

R. G. Ojemann Youmans - Neurological Surgery 4ª/e

Historia natural O Schwanoma Vestibular usualmente tem lento crescimento mas sua

progressão é imprevisível. Alguns cessam crescimento alguns regridem parcialmente e raramente alguns tem rápida progressão.

Bederson e colaboradores relataram 70 pacientes acompanhados clinicamente por não concordarem com a cirurgia ou por terem progressão sintomática. Após uma media de FU de 36 meses (de 6 a 84 meses) observou que No primeiro ano 29 pacientes (41%) não tiveram progressão tumoral detectável.

Destes, num segundo ano, dos 18 que submeteram-se a exames apenas 1 sofreu crescimento tumoral.

Regressão tumoral parcial ocorreu em 4 pacientes (6%)

Dois pacientes sofreram deterioro clinico sem mudança do volume tumoral.

Em 37 pacientes (53%), ocorreu crescimento tumoral, entre 1 e 17 mm (média 3.4 ± 0.5 mm) no primeiro ano,

De 23 pacientes acompanhados por um segundo ano, 21 mantiveram crescimento tumoral.

O crescimento tumoral não guardou correlação com idade duração de sintomas e volume tumoral inicial.

Crescimento tumoral rápido foi notado em 7 pacientes.

Anatomia

Fossa posterior

Cond. auditivo interno

Seios venosos

Pares cranianos

Cerebelo

Tronco encefálico

A escolha da

abordagem

depende da

locallização e

extensão

anatômica do

tumor

Acessos ao

Schwanoma

vestibular

Acesso pela

Fossa media

Acesso retrosigmoideo

Acesso ao APC

Acesso translabirintico

Atico

Canal semicircular horizontal

Canal semicircular posterior

Seio petroso

Seio sigmoide

N Facial

Preservação da função do nervo

facial Sistema de gradação :

House, J. W., and Brackmann, D. E.: Facial nerve grading system. Otolaryngol. Head Neck

Surg., 93:184, 1985.

40

50

60

70

80

90

100

Volume tumor

IC 0,9 1,9 2,9 3,9 > 4


facial

VOLUME TUMORAL Serie de 1985 – boa função facial

(graus 1 ou 2), após 1 ano de FU:

intracanalicular, 26 pacientes (96%);

0.0 a 0.9 cm, 37 pacientes (100 %);

1.0 a 1.9 cm, 122 pacientes (96 %);

2.0 a 2.9 cm, 96 pacientes (77 %);

3.0 a 3.9 cm, 102 pacientes (60 %);

Acima de 4.0 cm, 71 pacientes (58 %).

House, J. W., and Brackmann, D. E.: Facial nerve grading system. Otolaryngol. Head Neck Surg.,

93:184, 1985.


facial Evolução da

função facial

pós operatória:

PO imediato

1 ano

6 meses

Prakash Sampath, et al. Facial nerve injury in acoustic

neuroma (vestibular schwannoma) surgery: etiology and

prevention. Neurosurg Focus 5 (3):Article 4, 1998

Função facial, Literatura até 1997

Prakash Sampath, et al. Facial nerve injury in

acoustic neuroma (vestibular schwannoma)

surgery: etiology and prevention. Neurosurg

Focus 5 (3):Article 4, 1998

Preservação da função

do nervo facial

Evolução X volume

tumoral:

PO imediato

6 meses

Prakash Sampath, et al. Facial nerve injury in

acoustic neuroma (vestibular schwannoma)

surgery: etiology and prevention. Neurosurg

Focus 5 (3):Article 4, 1998


facial

Volume de risco

Para o centro de referencia de Leiden (University Medical Centre) o volume que correlaciona-se com maior poder preditivo da ocorrência de seqüela facial foi de 17.5mm, com sensibilidade e especificidade em 0.86 and 0.61. (permitindo predição 36% mais acurada em relação ao valor randômico prévio de 11mm.

Hastan, D. *; Godefroy, W. P. *; Malessy, M. J.A. +; van der Mey, A. G.L. *

Establishing a method to predict the outcome of vestibular schwannoma

surgery based on one's own results. Clinical Otolaryngology. 32(5):346-351,

October 2007.

Preservação da função facial

Jacob, Abraham MD; Robinson, Lawrence L. Jr MD; Bortman, Jared S. MD; Yu,

Lianbo PhD; Dodson, Edward E. MD; Welling, D Bradley MD, PhD Nerve of Origin,

Tumor Size, Hearing Preservation, and Facial Nerve Outcomes in 359

Vestibular Schwannoma Resections at a Tertiary Care Academic Center.

Laryngoscope. 117(12):2087-2092, December 2007.

Preservação da função facial

Jacob, Abraham MD.Nerve of Origin, Tumor Size, Hearing Preservation, and

Facial Nerve Outcomes in 359 Vestibular Schwannoma Resections at a

Tertiary Care Academic Center. Laryngoscope. 117(12):2087-2092, December

2007.

Preservação facial global 90%


facial Tipo do tumor :

Tumor sólido X tumor com componente cístico:

estudo de 70 pacientes com schwanoma cístico, operados por via translabiríntica, de 1981 a 2007, comparados a casos com tumor sólido, pareados nos parâmetros :

Gradação de House-Brackmann

Tamanho tumoral

Abrodahgem cirúrgica

Idade age

Não demonstrou diferença de gradação House-Brackmann,

2 anos após a cirurgia

Jones, Stephen E.M. M.B.B.S., F.R.C.S. (ORL-HNS) 1; Baguley, David M. Ph.D., M.Sc., M.B.A. 1;

Moffat, David A. B.Sc., M.A., F.R.C.S. 1 Are Facial Nerve Outcomes Worse Following Surgery

for Cystic Vestibular Schwannoma?. Skull Base: An Interdisciplinary Approach. 17(5):281-284,

July 2007.

Função do nervo facial

Em alguns pacientes o envolvimento do N.

Facial é intenso. Nestes casos as

decisões podem ser:

Deixar um pequeno remanescente da cápsula

tumoral (ressecção radical subtotal)

Dividir o nervo e aproximar suas bordas

Realizar enxertia com o nervo grande

auricular ou nervo sural.

Função do nervo facial Se o paciente desenvolver paralisia facial é

fundamental a proteção da córnea: Fechamento de pálpebra

Lagrima artificial

Pomada oftálmica

Tarsorafia

Peso de ouro na pálpebra

Se persistir a paralisia: Anastomose hopoglosso-facial total ou parcial

Procedimento ocular palpebral

Transposição de músculo temporal

Preservação da função coclear

Em 19984 Ojeman R.G. e colaboradores publicam serie de 22 casos de tentativa de preservação da audição nas cirurgias de SV.

47 publicações subsequentes atualizaram esta série. En 1988, Gardner e Robertson revisaram os relatos de preservação de audição em literatura inglesa, de 1954 a 1986. Até 1990 os dados de literatura não apontavam para melhoria dos resultados.

Uma das questões básicas era a definição de audição útil ou funcional. O critério mais aceito era o limiar de reconhecimento de fala menor que 50 dB e um índice de discriminação acima de 50%.

Ojeman R.G. usou indice de discriminação de 35 % por achar util para alguns pacientes.

Por outro lado Whittaker e Luetje enfatizaram que uma audição suficiente implicaria em índice de discriminação acima de 60%.


Segundo Ojeman, para pacientes com pelo

menos 35 % de discriminação de fala, no pré

operatório, a chance de preservação de

audição após a cirurgia era de:

60 % se tumor extender < 5 mm na fossa posterior

(FP).

36 % se extender de 0.6 a 1.5 cm na FP. .

Baixa probabilidade de preservação de audição se

tumor > 2 cm, independente da audição pre op.

Existem casos esporádicos de preservação de

audição em tumores mais volumosos.


Uma das formas de preservação da audição é o uso da monitorização funcional :

Pot Evocados auditivos Eletrococleografia, principalmente de curta

latencia (não afetados por anestesia).

Potenciais evocados do tronco cerebral

O Status dos componentes N1 e onda V tem clara correlação com o o resultado final


Resultados a longo prazo :

Shelton e colaboradores, em 8 anos de FU : 14 de 25 pacientes (56%) tiveram perda significativa de audição…

Palva e colaboradores apos 4 anos de FU : 2 de 13 pacientes tiveram perda significativa de audição

Rosenberg e associados não observaram declínio progressivo de audição, em 9 pacientes.

McKenna e colaboradores, em média de 5.4 anos de FU: 4 de 18 pacientes tiveram perda auditiva significativa

Samii e colaboradores : 50% de preservação da audição.

As alterações não se correlacionaram com : Tamanho do tumor, audição prévia, timming da cirurgia, sexo e idade.

Preservação da audição

Jacob, Abraham MD. Nerve of Origin, Tumor Size, Hearing Preservation, and

Facial Nerve Outcomes in 359 Vestibular Schwannoma Resections at a

Tertiary Care Academic Center. Laryngoscope. 117(12):2087-2092, December

2007.

Preservação da audição

Jacob, Abraham MD. Nerve of Origin, Tumor Size, Hearing Preservation, and Facial Nerve

Outcomes in 359 Vestibular Schwannoma Resections at a Tertiary Care Academic Center.

Laryngoscope. 117(12):2087-2092, December 2007.

Conclusões

“It is possible to remove VS completely while functionally preserving the facial and cochlear nerves. An elaborated microsurgical technique accompanied by continuous electrophysiological monitoring leads to preservations rates greater than 98% for the facial and approximately 50% for the cochlear nerve, independent of tumor size.”

Amir Samii, M.D., Ph.D.

Neurosurgery 60[ONS Suppl 1]:ONS-124–ONS-128, 2007

Anatomia osso

The dimensions of the posterior fossa differ among patients. The distance from the transverse sinus to the floor of the posterior fossa may vary by more than 1 cm in different individuals. The internal auditory meatus lies approximately 1 cm anterior and superior to the jugular foramen; however, these landmarks are closer in some patients. Just above and often slightly anterior to the internal auditory meatus is a prominence of bone. The internal auditory meatus is usually 5 to 7 mm in diameter, and it leads to a canal that measures about 1 cm to the transverse crest. Bone can be removed to the level of the crest, but lateral to this the labyrinth may be injured.50

CRANIAL NERVES

Cranial Nerve IV. The trochlear nerve is seen in the tentorial notch lying on the brain stem parallel to the tentorial edge and above the trigeminal nerve. It may be adherent to the capsule of large tumors.

Cranial Nerve V. The broad trigeminal nerve is located about 1 cm anterior to the internal auditory meatus. This distance can vary, and the nerve may be displaced directly anteriorly or anterosuperiorly by the tumor. In the suboccipital approach, the large sensory component generally hides the anteriorly displaced motor branch from view. The nerve fibers course medially and slightly downward and backward to enter the pons through the middle cerebellar peduncle.

Cranial Nerve VI. The abducens nerve emerges from the anterior surface of the brain stem in a sulcus between the inferior border of the pons and the upper end of the pyramid. The nerve passes anteriorly and laterally through the cerebellopontine angle to enter the dura at the base of the sphenoid bone. From the suboccipital view, the nerve is usually seen deep in the space between the seventh and eighth cranial nerve complex and the ninth and tenth nerves. This nerve may be adherent to large tumors.

Anatomia osso

The dimensions of the posterior fossa differ among patients. The distance from the transverse sinus to the floor of the posterior fossa may vary by more than 1 cm in different individuals. The internal auditory meatus lies approximately 1 cm anterior and superior to the jugular foramen; however, these landmarks are closer in some patients. Just above and often slightly anterior to the internal auditory meatus is a prominence of bone. The internal auditory meatus is usually 5 to 7 mm in diameter, and it leads to a canal that measures about 1 cm to the transverse crest. Bone can be removed to the level of the crest, but lateral to this the labyrinth may be injured.50

CRANIAL NERVES

Cranial Nerve IV. The trochlear nerve is seen in the tentorial notch lying on the brain stem parallel to the tentorial edge and above the trigeminal nerve. It may be adherent to the capsule of large tumors.

Cranial Nerve V. The broad trigeminal nerve is located about 1 cm anterior to the internal auditory meatus. This distance can vary, and the nerve may be displaced directly anteriorly or anterosuperiorly by the tumor. In the suboccipital approach, the large sensory component generally hides the anteriorly displaced motor branch from view. The nerve fibers course medially and slightly downward and backward to enter the pons through the middle cerebellar peduncle.

Cranial Nerve VI. The abducens nerve emerges from the anterior surface of the brain stem in a sulcus between the inferior border of the pons and the upper end of the pyramid. The nerve passes anteriorly and laterally through the cerebellopontine angle to enter the dura at the base of the sphenoid bone. From the suboccipital view, the nerve is usually seen deep in the space between the seventh and eighth cranial nerve complex and the ninth and tenth nerves. This nerve may be adherent to large tumors.

Cranial Nerves VII and VIII. The facial nerve and vestibulocochlear nerves emerge from the lateral surface of the brain stem close to the inferior border of the pons. Rhoton has beautifully described and illustrated this anatomical relationship, aiding in the identification and dissection of the facial nerve.51 The facial nerve arises from the brain stem near the lateral end of the pontomedullary sulcus, 1 to 2 mm anterior to the point at which the vestibulocochlear nerve joins the brain stem at the lateral end of the sulcus. In patients with large tumors, the nerves are usually displaced apart, but in those with small tumors the facial nerve is often hidden anterior to the vestibulocochlear nerve and can be seen only with displacement of this nerve. The facial nerve has a constant relationship to the junction of the glossopharyngeal, vagus, and accessory nerves with the lateral side of the medulla. The facial nerve arises 2 to 3 mm above the most rostral rootlet contributing to these nerves. In exposing the tumor, the flocculus is seen projecting into the cerebellopontine angle just posterior to the point at which the facial and vestibulocochlear nerves join the pontomedullary sulcus. Another landmark is the choroid plexus projecting from the foramen of Luschka, which lies on the posterior surface of the glossopharyngeal and vagus nerves just inferior to the junction of the facial and vestibular nerves with the brain stem.

In the cerebellopontine angle, the seventh and eighth cranial nerves course laterally and slightly upward to enter the internal auditory meatus and canal. At the lateral end of the canal, the transverse crest separates the facial nerve and superior vestibular nerve above from the cochlear nerve and inferior vestibular nerve below. A bony ridge separates the facial nerve and nervus intermedius anteriorly from the superior vestibular nerve posteriorly.

In the posterior fossa, the facial nerve is usually on the anterior surface of the tumor, as one would expect with the tumor arising from the vestibular nerve. However, the facial nerve can be displaced around the superior pole, the inferior pole, or, rarely, across the posterior surface of the capsule. Koos and Perneczky found that in patients with the largest tumors, the location of the facial nerve was as follows: anterior, 73 per cent; superior, 10 per cent; inferior, 8 per cent; and posterior, 9 per cent.23 In the series of Sugita and Kobayashi, the facial nerve was as follows: anterior, 50 per cent; superior, 30 per cent; inferior, 15 per cent; and posterior, 2 per cent.60 The author has found the posterior location in only 1 per cent of these patients. Rhoton found that the facial nerve in the internal auditory canal was usually displaced anteriorly but could also be in an anterior superior or anterior inferior location.50

Cranial Nerves IX, X, and XI. The glossopharyngeal, vagus, and accessory nerves are seen during the initial exposure of the cerebellopontine angle. The accessory nerve enters the posterior fossa through the foramen magnum and turns laterally on the dura toward the jugular foramen. The vagus and glossopharyngeal nerves arise from the lateral medulla between the inferior cerebellar peduncle and the oliva and pass through the central part of the jugular foramen, with the inferior petrosal sinus anteriorly and the sigmoid sinus posteriorly. The glossopharyngeal nerve lies in the anterior part of the foramen and is separated from the vagus nerve by a band of fibrous tissue.

Exames complementares

Audiography documents hearing loss in almost all patients with acoustic neuroma when they first seek medical attention.

The characteristic finding is a sensorineural hearing loss characterized by poorer speech discrimination than would be anticipated from the findings on pure-tone audiometric testing.

The most common pure-tone abnormality is a high-frequency loss; however, a flat loss, low-tone loss, or trough-shaped loss may be observed.20

Pure-tone audiometry and speech discrimination testing are the only audiometric tests now performed on a regular basis.

Diagnostico histológico

The histological criteria for the diagnosis of acoustic neuroma are the same as those of schwannomas that arise from other nerves.14, 59§59

The classic description of a schwannoma is tissue composed of densely packed elongated spindle cells in interlocking fascicles with a tendency toward palisading (Antoni type A tissue), often intermingled with loosely textured tissue with extracellular clear spaces that sometimes are associated with cyst formation (Antoni type B tissue) and, frequently, with nuclear atypia. Varying patterns can be seen.

Other findings may include Verocay bodies, hemosiderin deposition, hyalinized blood vessels, malformation-like vessels, recent and old thromboses, sheets of foam macrophages, foci of high cellularity, whorls, and collagenous scarring.

Sobel found lobular growth patterns in about 40 per cent and meningioma tissue in 20 per cent of patients with neurofibromatosis type 2.59§59

Indicações de tratamento INDICATIONS FOR SURGERY

1. Recent or worsening symptoms except in elderly patients with mild symptoms

2. The possibility of preservation of useful hearing

3. Enlargement of the tumor in patients who are being followed except in elderly patients with small or medium-sized tumors

4. Regrowth after subtotal removal in younger patients

5. Enlargement of a tumor after radiosurgery once the initial swelling reaction has subsided

6. The patient's decision after discussion of the treatment options

INDICATIONS FOR RADIATION THERAPY OR RADIOSURGERY

1. Enlargement of small or medium-sized tumors in elderly patients with mild symptoms who are being followed

2. Regrowth after subtotal removal

3. Major medical illness that significantly increases the risk of operation


INDICATIONS FOR OBSERVATION

1. A long history of auditory symptoms in patients of any age and with tumors of any size

2. Mild symptoms in elderly patients

3. An incidental finding of a tumor on scanning for some other reason


Técnicas cirúrgicas

The microsurgical removal of an acoustic neuroma can be achieved with

A suboccipital approach - When an attempt is being made to preserve hearing, the author and his neuro-otology colleagues usually use the suboccipital approach. For most patients, the author has preferred the suboccipital (posterior fossa) approach because of the wide visualization that it allows, the ability to save hearing in appropriate cases, and the good results obtained with its use. The details of the middle fossa approach have been described by Brackmann.

A translabyrinthine approach - The details of the translabyrinthine approach have been described by House and Hitselberger.

A middle fossa approach - some surgeons prefer the middle fossa approach. The author uses this approach when the tumor is located in the lateral end of the internal auditory canal.

Good results from all three approaches have been reported by groups of experienced surgeons.45 A high percentage of patients can be cured with resultant low morbidity and mortality.

Both the suboccipital and the translabyrinthine approaches have been used to remove tumors of all sizes.

Resulotados de cirurgia

Results of Suboccipital Operation for Unilateral Acoustic Neuroma

Good results using the suboccipital (posterior fossa) approach for removal of unilateral acoustic neuromas have been reported by many surgeons.1, 6, 8, 22, 23, 53, 61§1 A personal series of 461 patients with unilateral acoustic neuromas managed with a suboccipital approach in conjunction with an otologist has been reviewed.43 Tumors are categorized as intracanalicular or by their extension into the posterior fossa at 1.0-cm intervals.

The functional results of the operation are reported as good, fair, or poor. The term "good" was used for those patients who were free of major neurological deficit and who returned to their pre-illness level of activity. Seventh and eighth cranial nerve function was not considered. "Fair" described patients who were functionally independent but not able to return to their previous full-time activity because of a neurological deficit or because of a significant preoperative neurological deficit that, although usually improved, continued to cause disability. Many of these patients returned to work and lead essentially normal lives. The term "poor" described those patients who were dependent because of a major new or preoperative neurological disability. In the overall series, 99 per cent of patients were independent in their activities. All patients with tumors up to 1.0 cm in diameter had a good result, as did 96 per cent of those with tumors 1.0 to 1.9 cm in diameter and 93 per cent of those with lesions 2.0 to 2.9 cm in diameter. Even patients with large tumors had an 80 per cent chance of attaining a good outcome. The most common reason for the fair results was impairment of balance, gait, or coordination. Dysarthria or diplopia occurred in some patients. In 6 of the 43 patients with a fair outcome, significant preoperative deficits improved but still limited activity. In a small percentage of patients, a significant problem with headache lasted longer than expected and in two patients prevented full recovery, resulting in their inclusion in the fair result category.

Two poor results and two deaths occurred (operative mortality, 0.5 per cent). The poor results were due to a stroke caused by a middle cerebral embolus and to the effects of an intraoperative brain stem hemorrhage. One death was of a 69-year-old woman who made a full recovery only to develop chronic meningitis that progressed over several months with no diagnosis and no response to treatment. The other operative mortality followed a hemorrhage into the cerebellum and brain stem during the removal of a tumor 4 cm in diameter.

EXTENT OF TUMOR REMOVAL

AND RECURRENCE The goal of the operation is total removal of the tumor. However, this goal must be tempered by surgical judgment that considers the need to preserve

and improve function as well as long-term results. The author's experience indicates that subtotal and radical subtotal resections of acoustic neuromas are substantiated because their associated recurrence rate and, in patients with large tumors, the incidence of postoperative neurological problems have been low. This has been noted to be especially true in elderly patients.

Radical subtotal removal describes those procedures in which a small fragment of tumor is left, usually because it is densely adherent to the facial nerve or brain stem (Fig. 129-17). The term "subtotal removal" is used to describe those cases in which an extensive removal of tumor has been performed but in which a portion of the rim of the tumor capsule is left attached to the brain stem and cranial nerves (Fig. 129-18).

When a radical subtotal or subtotal removal has been selected, the rate of recurrence should be carefully evaluated. Over the 15 years of the series of 461 patients, none of the 43 patients with radical subtotal removal has had recurrence requiring treatment. These patients have been followed for 1 to 14 years (average, 5.4 years). The tumors of seven of the patients could not be seen on follow-up scanning.

In this series, 9 of 56 patients with subtotal removal (16 per cent) had recurrence requiring treatment (average duration of follow-up, 5.2 years). Treatment of the recurrence included total removal of the tumor in four patients, radical subtotal removal in one, radiation therapy in two, and another subtotal removal in two. One patient with subtotal removal and the patient with radical subtotal removal have showed no further growth over 4 years. The other patient with a second subtotal removal had an aggressive regrowth of her tumor and she is considering radiation therapy.

Recurrence can also occur following apparent total removal of a tumor. The known recurrence rate in this series was 0.8 per cent (i.e., 3 of 360). The first patient with recurrence was 69 years of age. She exhibited extensive recurrence over 2 years and had another apparent total removal. Subsequent magnetic resonance imaging over 3 years showed no recurrence. The second patient had a diagnosis of recurrence at 5 years after surgery. She received fractionated radiation therapy, and no change was observed over the subsequent 4 years. The last patient had a small tumor detected on her first magnetic resonance imaging 9 years after surgery. Repeat imaging over 2 years demonstrated no change.

Wazen and colleagues found that in 9 of 13 patients with subtotal removal (aged 66 to 81 years), no growth in the residual tumors was observed in the follow-up period, which ranged from 6 months to 15 years.67 Klemink and co-workers reported on 20 patients who had incomplete removal of their tumors in an attempt to reduce the operative risks.21 Two groups were defined—{emdash}one comprising patients with subtotal resection (resection of less than 95 per cent of the tumor), and the other consisting of patients with near-total removal (resection of 95 per cent or more of the tumor). The subtotal resection group included mostly elderly patients (mean age, 68.5 years) with large tumors. The near-total resection group consisted of young patients (mean age, 45.8 years). The mean duration of follow-up was 5 years, and only one patient showed regrowth. Lownie and Drake reported that 9 of 11 patients followed for 10 to 22 years after radical intracapsular removal did not have recurrence.28§28 The two recurrences were at 2 and 3 years postoperatively.

Radiocirurgia

The growth of an acoustic neuroma can be arrested in some patients with the use of radiation therapy or radiosurgery. Experience with gamma irradiation, linear accelerator, proton beam, and fractionated conventional therapy has been reported.9, 29, 66§9

Results of treatment with stereotactic radiosurgery and the 201-source cobalt-60 gamma unit have been reported by a Pittsburgh group.29 Of 96 patients with unilateral acoustic neuromas and minimum 6-month follow-up, 68 of the tumors (71 per cent) were unchanged, 25 (26 per cent) were smaller, and 2 (2 per cent) were larger. The incidence of a delayed facial nerve weakness was 29 per cent, with recovery in approximately 90 per cent of patients. The preservation of useful hearing (as defined by this group, greater than 50 per cent speech discrimination score and less than 50 dB loss in pure-tone average) was 34 per cent at 2 years in the 37 per cent of patients with useful hearing preoperatively. Trigeminal neuropathy occurred in 33 per cent, but it tended to be mild and temporary. A few patients developed new parenchymal changes in the middle cerebellar peduncle and pons as seen on magnetic resonance imaging. No associated symptoms were noted, and these changes tended to resolve. Four patients required a ventriculoperitoneal shunt for hydrocephalus within 1 year of having radiosurgery.

ACOUSTIC SCHWANNOMA

With the obvious exception of the optic nerves, the cranial nerves are myelinated by Schwann cells and are therefore potential sites for schwannomas. In practice, only one, the eighth cranial nerve, is commonly affected. The fifth is worthy of mention but is nevertheless a very distant second.

In the eighth cranial nerve, the transition from the central to the peripheral nervous system occurs approximately 1 cm out along its course just as it exits, or enters, the internal auditory meatus. For this reason, vestibular schwannomas are associated with distinctive flaring of the auditory meatus and auditory canal.

The lesions are usually unilateral but are bilateral in neurofibromatosis type 2.

the biological behavior of the schwannoma is one of slow growth, and, like other true schwannomas, malignant degeneration is exceedingly uncommon.136§136 Primary malignant neoplasms of the cranial nerves, particularly the fifth, are recognized but often have an unproven relationship to the Schwann cell.

Vestibular schwannomas are the most

common cerebellopontine angle tumors in

adults but rarely occur in children, except

those with neurofibromatosis.

Neurofibromatosis Type 2

Neurofibromatosis type 2 is much less common than neurofibromatosis type 1 with an incidence of approximately 1 in 40,000 births.

Molecular Genetics The gene for neurofibromatosis type 2 (NF2) has been identified on chromosome 22. The gene product, named merlin (or schwannomin), has been localized to the cell membrane. Merlin belongs to a family of proteins that act as membrane organizers, linking integral membrane proteins with cytoskeletal elements.109, 133§109, 133 It is possible that merlin contributes to the maintenance of cell shape, participates in cell adhesion to the extracellular matrix, and is involved in intercellular communication. Mutations have been identified in the NF2 region in the germ line of patients with this disorder.109§109 In addition, somatic mutations have been identified in schwannomas and meningiomas in neurofibromatosis type 2 patients with an identified germ line mutation, supporting the hypothesis that the NF2 gene has tumor suppressor function.109§109 Inactivation of this gene may be a common occurrence in sporadic meningiomas and has also been identified in other tumor types.7, 112§7

recidiva

Concern about recurrence following removal of an acoustic neuroma with preservation of the cochlear nerve has been discussed in the literature. Thedinger and colleagues emphasize that inadequate exposure of the lateral end of the internal auditory canal may be associated with the leaving of a remnant of tumor.65§65 Neely reported that in patients in whom all of the tumor appeared to have been removed, residual tumor was found in the cochlear nerve, and he concluded that, "histologic data suggest that complete tumor removal in attempts to preserve hearing may be beyond our surgical capabilities."38 However, Samii and associates reported no recurrence in 16 patients followed 1 to 8 years after undergoing removal of intracanalicular acoustic neuromas with anatomical preservation of the cochlear and facial nerves.53 In our series, an attempt to preserve hearing was made in 119 patients with tumors less than 2.0 cm in diameter. Follow-up computed tomography and magnetic resonance imaging have shown no definite recurrence in those in whom the cochlear nerve was kept intact. A few patients have an area of gadolinium enhancement in the internal auditory canal on postoperative magnetic resonance imaging. Whether this represents residual tumor or postoperative scar is unknown, but this finding has remained unchanged on follow-up scanning.

Tinnitus may persist in the ear following removal of an acoustic neuroma. There does not seem to be any difference in the incidence of tinnitus in those patients who had the cochlear nerve preserved to save hearing and in those in whom the cochlear nerve was divided to remove the tumor.13§13

preservação da função do nervo facial schwanoma...

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