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The Laryngoscope Lippincott Williams & Wilkins, Inc. © 2003 The American Laryngological, Rhinological and Otological Society, Inc.
Inner Ear Extension of Vestibular Schwannomas Maurizio Falcioni, MD; Abdelkader Taibah, MD; Di Giuseppe Trapani, MD; Tarek Khrais, FRCS, HSD, MD; Mario Sanna, MD
Objective: Inner ear extension of vestibular schwannomas (VSs) is a rare finding but has important clinical implications. This report reviews the treatment options and presents the experience of the Gruppo Otologico, Piacenza, Italy, in this field. Study Design: Case report and literature review. Methods: Five cases of VSs with inner ear extension were surgically removed. In all of them, the cochlea was partially or completely invaded by the lesion. Results: In 4 cases, the inner ear extension was preoperatively identified on magnetic resonance imaging, and the surgical removal was planned through a transotic approach. In the last case, the cochlear invasion was not detected preoperatively, and the lesion was removed during a second surgery performed to seal a cerebrospinal fluid fistula. Conclusions: VSs with inner ear extension should be distinguished from pure intralabyrinthine schwannomas because of differences in clinical significance. Cochlear involvement is more frequent than vestibular involvement and is often accompanied by a dead ear. Dead ear caused by small VSs should alert the surgeon to the possibility of a cochlear extension. The presence of an intracochlear involvement requires the adoption of an approach that allows control of the cochlear turns, and we found the transotic approach to be the most suitable. Undetected cochlear extensions that are left in place may grow with time. Key words: Vestibular schwannoma, vestibule, cochlea, inner ear, labyrinth. Laryngoscope, 113:1605–1608, 2003
INTRODUCTION Until the late 1980s, schwannomas confined to the labyrinth were reported almost exclusively as intraoperative or postmortem finding. The situation changed after the introduction of magnetic resonance imaging (MRI), when the preoperative discovery of intralabyrinthine schwannomas (ISs) became more frequent. In our opinion, these lesions should be distinguished from labyrinthine From the Gruppo Otologico, Piacenza, Italy. This work was supported by a grant from A.S.A.B. (Associazione Studio Aggiornamento Basicranio). Editor’s Note: This Manuscript was accepted for publication May 7, 2003. Send Correspondence to Maurizio Falcioni, MD, Gruppo Otologico, Via Emmanueli 42, 29100 Piacenza, Italy. E-mail: maurizio.falcioni@ gruppootologico.it
Laryngoscope 113: September 2003
involvement by vestibular schwannomas (VSs) because of the different clinical implications. The following study reports 5 cases of VSs with inner ear invasion surgically treated at the Gruppo Otologico, Piacenza, Italy. A summary of the main features of the five cases is reported in Table I.
CASE REPORTS Case 1 A 24-year-old man reported a sudden right-sided hearing loss (HL) and tinnitus for 2 years, in the absence of any vestibular complaints. Audiometry revealed the presence of right-sided anacusis. MRI showed a right-sided internal auditory canal (IAC) neoformation that invaded the basal turn of the cochlea. Cochlear extension was not mentioned on the radiologic report. Surgical removal was accomplished through a transotic (TO) approach. The patient was discharged after 5 days with normal facial function. At follow-up after 1 year, the MRI did not show any tumor recurrence.
Case 2 A 49-year-old woman reported a progressive left-sided HL over 13 years, accompanied by occasional tinnitus and vertigo. Audiometry revealed the presence of left-sided dead ear. MRI showed a cerebellopontine angle neoformation (size 1 cm) with invasion of the cochlea. Cochlear extension was not mentioned on the radiologic report. The tumor was removed through a TO approach. The patient was hospitalized for 6 days and discharged with a facial nerve (FN) dysfunction (grade III according to the House-Brackmann scale). At the last follow-up, 1 year after surgery, the FN function had recovered to grade II.
Case 3 A 26-year-old woman reported a progressive right-sided HL and tinnitus over 1 year. She did not experience any vestibular disturbances. Audiometry revealed the presence of right-sided dead ear. MRI revealed an intracanalicular neoformation. No inner ear extension was mentioned on the radiologic reports of the two MRI scans that had been done elsewhere. The tumor was removed through a translabyrinthine approach (TLA). After 3 days, the patient experienced a rhino-liquorrhea. Reevaluation of the preoperative MRI showed the presence of tumoral extension into the basal turn of the cochlea (Fig. 1). During the revision surgery for closure of the cerebrospinal fluid fistula, the cochlea was drilled, and the residual tumor was removed. The patient was hospitalized for 9 days and discharged with a FN palsy. One
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TABLE I. Patient Features. Patient
Symptoms
Hearing
Symptoms Duration
Inner ear Involvement
IAC/CPA Involvement
1 2
HL, tinnitus HL, tinnitus, vertigo HL, tinnitus
Dead ear Dead ear
2 years 13 years
Basal turn Cochlea
Dead ear
1 year
3 4 5
HL, tinnitus, Dead ear vertigo HL, Dead ear unsteadiness
24 years 5 years
Middle Ear Involvement
Radiological Report
Preoperative Detection
Approach
IAC CPA (1 cm)
NO NO
No IE involvement No IE involvement
YES YES
TO TO
Basal turn
IAC
NO
NO
All
CPA (3 cm)
YES
No IE involvement (2 MRI) No IE involvement
YES
Cochlea
IAC
NO
No IE involvement
YES
TLA and revision TO TO
IAC ⫽ internal auditory canal; CPA ⫽ cerebellopontine angle; HL ⫽ hearing loss; IE ⫽ inner ear; TO ⫽ transotic approach; TLA ⫽ translabyrinthine approach;MRI ⫽ magnetic resonance imaging.
year later, the MRI showed no recurrence, and the FN function had recovered to a grade III.
Case 4 A 48-year-old woman reported a left-sided tinnitus over 24 years accompanied by a left-sided progressive HL over 13 years. She also experienced one episode of vertigo. Audiometry revealed the presence of left-sided dead ear. The MRI showed a 3 cm cerebellopontine angle neoformation extending to the IAC, all the inner ear, as well as the geniculate ganglion (Fig. 2). Both the inner ear and geniculate ganglion involvement were not mentioned on the radiologic report. The computed tomography (CT) scan showed an IAC enlargement and the presence of soft tissue in middle ear near the round window (Fig. 3). The geniculate fossa was enlarged as well. Tumor removal was planned through a TO approach. During the surgery, two different lesions were disclosed, originating respectively from the VIII and VII cranial nerve. The tumor filled all the inner ear protruding into the middle ear cavity through the round window. It was not possible to locate the central stump of the FN. The patient was hospitalized for 6 days and discharged with a total palsy of the VII cranial nerve. Two months later, the patient underwent hypoglosso-facial anastomosis. At the first follow-up, 3 months after the last surgery, the FN function was still grade VI.
Case 5 A 54-year-old man reported a right-sided HL and unsteadiness over 5 years. Audiometry revealed the presence of rightsided dead ear. The MRI showed an IAC lesion involving all the cochlea turns (Fig. 4). Surgical removal was planned through a TO approach. The patient was hospitalized for 4 days and discharged with a normal FN function (grade I). Because he was operated on only few months ago, no follow-up is presently available.
DISCUSSION Histologically, VSs develops in the myelinated part of the VIII cranial nerve, often in the IAC. However, Schwann cells are also present in the modiolus, close to the spiral ganglia1, so schwannomas theoretically may arise in this area. The first report of an IS is attributed to Mayer, in 1917.2 It was discovered at autopsy in a patient affected by neurofibromatosis. Since then, a few cases have been reported as postmortem or intraoperative findings during surgery for Me´ nie`re’s disease.3 The first preoperative raLaryngoscope 113: September 2003
1606
diologic diagnosis of an intracochlear schwannoma was reported by Karlan et al.4 in 1972, through a polytomography demonstrating nonvisualization of the basal turn of the cochlea. In 1994, Doyle and Brackmann5 reported the first series of preoperatively diagnosed ISs through MRI. Currently, refinements in the MRI technique allow the differentiation of lesions developing in the inner ear, including small tumors.6 The increased frequency of reporting ISs during the last years has coincided with the development of the MRI. In some articles, pure ISs have been listed together with labyrinthine involvement by VSs.5,7,8 In agreement with Zbar et al.9, we think that the two lesions should be distinguished from each other because of the different clinical implications and, probably, the different site of origin. In fact, although it is not possible to definitively identify the origin of a schwannoma with IAC and inner ear involvement,10 the hypothesis of a progressive involvement of the labyrinth during the growth of a VS seems to be more reasonable. This is supported by the fact that cochlear involvement is more frequent than vestibular involvement. This difference can be explained by the presence of the weakest part of the fundus, the cribriform area, between the IAC and the cochlea.11 All our cases showed involvement of the cochlea. Two of the smallest tumors (cases 1 and 3) had a minimal inner ear component, confined to the basal turn of the cochlea, as if discovered at the beginning of the invasion. If the tumor’s origin was in the cochlea, it is difficult to understand why such a tumor should first erode the cribriform area before growing along the way of least resistance offered by the cochlear turns. However, it seems reasonable to suppose the tumor originated from the cochlear nerve.12 This is in agreement with our surgical finding in which, in all three small tumors, there was a clear involvement of the cochlear nerve. In the two remaining lesions, the IAC was completely filled by the lesion, and it was not possible to establish the nerve of the origin. In rare cases, the tumor involving the inner ear can have further growth into the middle ear, through the oval window or the round window. Because of the natural barrier represented by the footplate, the round window Falcioni et al: Extension of Vestibular Schwannomas
www.medicsindex.com
route is more probable and has been reported more frequently in literature.11,13,14 In one of our patients, the tumor completely filled the inner ear, with a small component protruding into the middle ear cleft through the round window. This extension was visible on MRI and was further confirmed by a CT scan. As already reported, CT scan is useful as a complementary evaluation for schwannomas involving the middle ear, allowing a clear definition of the lesion’s extent and its relationship with the surrounding structures.11 HL, tinnitus, and vertigo are the symptoms usually reported in presence of an IS. It seems that vertigo is related only to the involvement of the posterior labyrinth.5 This may not be the case in VSs with inner ear extension because the symptomatology is also related to the retrocochlear component of the tumor. All of our five cases presented with HL that progressed to anacusis at the time of diagnosis. Vertigo was reported at the beginning of the symptoms by two patients. Dead ear seems to be particularly common in cases of VSs with cochlear involvement.5 As a consequence, the contemporary presence of a dead ear and a VS should prompt the surgeon to carefully evaluate the MRI to detect any lateral extension into the cochlea. Although toxic and metabolic theories have also been proposed, HL in these patients seems to be related to the direct cochlear invasion.15 Labyrinthine invasion is clearly visible on MRI as an enhanced mass lateral to the IAC fundus after gadolinium infusion or as a lack of inner ear fluid in the fast spin echo sequences. However, particularly in cases with limited inner ear involvement, this component of the lesion can be overlooked with a nonaccurate scan evaluation. In all our cases, the inner ear extension was not pointed out in the radiologic report. All the scans had been carried out in other centers, probably without adequate experience in petrous bone and cerebellopontine angle (CPA) lesions, and those incomplete reports could have been of particular significance when planning the surgical removal. In four cases, the labyrinthine component was identified by the physicians of Gruppo Otologico during office scan evaluation, but in one patient, the cochlear extension escaped this reassessment (case 3). From a clinical point of view, management of pure IS depends only on symptomatology, in particular the presence of vertigo. If no disabling vertigo is present, the tumor can be radiologically monitored.8 On the contrary, VSs involving the inner ear should be treated according to the IAC/CPA extension, and the patient’s age and wishes. In both instances, no hearing preservation procedure is feasible. The only pure IS patient that presented to our center has been conservatively treated and is being radiologically monitored. All five cases of VSs with inner ear extension presented in this series have been surgically treated. In the four cases in which the inner ear involvement has been preoperatively detected, the removal was planned through a TO approach.16,17 The last case was originally treated by means of a TLA, and the tumor remnants inside the cochlea were discovered during reevaluation of the preoperative scan because of the development of a rhinoliquorrea. A revision surgery was then planned, allowing removal of the residual lesion and cloLaryngoscope 113: September 2003
Fig. 1. Magnetic resonance imaging, axial view, patient 3. The scan shows an internal auditory canal lesion with an extension to the basal turn of the cochlea.
sure of the cerebrospinal fluid fistula. Green and McKenzie7 reported two cases in which a VS with undetected cochlear extension was treated with a TLA, leaving the inner ear component of the tumor. One patient required a revision surgery, whereas the other did not show any tumor growth on serial MRI. The classic TLA allows opening and control of the vestibule and semicircular canal while the cochlea remains inaccessible. In contrast, in the TO approach, the external and middle ear are removed, the external auditory canal is closed as a blind sac, and the cochlea is drilled out. Although this approach is more time consuming, it allows a direct control of any tumor extension inside the cochlea. As a consequence, in the presence of an intralabyrinthine extension of a VS, the TLA can be adopted only when the intralabyrinthine component is limited to the vestibule and the semicircular canals, whereas involvement of the cochlea requires management through a TO approach. The retrosigmoid approach, not allowing access to the inner ear, is contrain-
Fig. 2. Magnetic resonance imaging, axial view, patient 4. A large lesion involving the cerebellopontine angle and internal auditory canal. Enhancement of the cochlea, vestibule, and lateral semicircular canal is also clearly visible.
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Fig. 3. Computed tomograph, coronal view, patient 4. The tumor protrudes from the round window, partially occupying the middle ear cleft.
dicated in the presence of intralabyrinthine tumoral extension. Takizawa et al.18 reported two cases of recurrence after a retrosigmoid approach in patients affected by VSs with intralabyrinthine extensions. Both recurrences occurred mainly in the extradural space. The middle cranial fossa approach theoretically can offer a good exposure of all the vestibule and the turns of the cochlea. However, because complete tumor removal in this pathology requires the sacrifice of hearing, use of such a procedure, which was originally meant to preserve hearing, does not make sense.
CONCLUSIONS Currently, inner ear involvement by VSs is more frequently reported because of the use of high-resolution MRI. In our opinion, VSs with labyrinthine extension should be distinguished from pure ISs because of the different clinical significance and, probably, the different
Fig. 4. Magnetic resonance imaging, axial view, patient 5. The fundus of the internal auditory canal is filled by a lesion extending to the basal turn of the cochlea.
Laryngoscope 113: September 2003
1608
origin. According to our data, involvement of the cochlea is more frequent than vestibular involvement and is often accompanied by a dead ear. Cochlear invasion by a VS should always be looked for on the MRI, especially in presence of a dead ear, and, because such extensions could be missed by radiologists, the surgeon should personally evaluate the MRI for their presence. The presence of an intracochlear tumoral extension requires the adoption of an approach allowing direct control of the cochlear turns. Because it is impossible to preserve any hearing, the TO approach seems to be the most appropriate procedure. Undetected cochlear extensions left in place during surgery may grow with time and require a revision surgery. Theoretically, because of the frequent anacusis present in these patients, this growth may go on asymptomatically until the tumor reaches considerable size.
BIBLIOGRAPHY 1. Anson BJ, Donalson JA. Surgical Anatomy of the Temporal Bone. Philadelphia: WB Saunders, 1981. 2. Mayer O. Ein Fall von multiplen Tumoren in den Endansbreintungen des Akustikus. Z Ohrenheilk 1917;75: 95–113. 3. Sataloff RT, Roberts BR, Feldman M. Intralabyrinthine schwannoma. Am J Otol 1988;9:323–326. 4. Karlan MS, Basek M, Potter GB. Intracochlear neurilemmoma. Arch Otolaryngol 1972;96:573–575. 5. Doyle KJ, Brackmann DE. Intralabyrinthine schwannomas. Otolaryngol Head Neck Surg 1994;110:517–523. 6. Hegarty JL, Patel S, Fischbein N, et al. The value of enhanced magnetic resonance imaging in the evaluation of endocochlear disease. Laryngoscope 2002;112:8 –17. 7. Green JD, McKenzie D. Diagnosis and management of intralabyrinthine schwannomas. Laryngoscope 1999;109: 1626 –1621. 8. Fitzgerald DC, Grundfast KM, Hecht DA, Mark AS. Intralabyrinthine Schwannomas. Am J Otol 1999;20:381–385. 9. Zbar RIS, Megerian CA, Khan A, Rubinstein JT. Invisible culprit: intralabyrinthine schwannomas that do not appear on enhanced magnetic resonance imaging. Ann Otol Rhinol Laryngol 1997;106:739 –742. 10. Donnelly MJ, Daly CA, Briggs RJ. MR imaging features of an intracochlear acoustic schwannoma. J Laryngol Otol 1994; 108:1111–1114. 11. Amoils CP, Lanser MJ, Jackler RK. Acoustic neuroma presenting as a middle ear mass. Otolaryngol Head Neck Surg 1992;107:478 – 482. 12. Barbieri M, Bruzzo M, Mora R, et al. Cochlear schwannomas. Skull Base 2001;11:241–244. 13. Storrs LA. Acoustic neuromas presenting as a middle ear tumors. Laryngoscope 1974;84:1175–1180. 14. Julian GG, Harnsberger HR, Shelton C, Davidson HC. Imaging case of the month: translabyrinthine schwannoma. Am J Otol 1998;19:246 –247. 15. Roland PS, Glimore J. Intracochlear schwannoma. Otolaryngol Head Neck Surg 1998;119:681– 684. 16. Fisch U, Mattox D. Microsurgery of the Skull Base. New York: Thieme Medical Publishers, 1988. 17. Sanna M, Saleh E, Panizza B, et al. Atlas of Acoustic Neurinoma Microsurgery. Stuttgart-New York: Georg Thieme Verlag, 1998. 18. Takizawa T, Tanaka Y, Miyairi Y, et al. Acoustic neuroma involving the labyrinth: two case reports. In: Sanna M, Taibah A, Russo A, Mancini F eds. Acoustic Neurinoma and Other CPA Tumors. Bologna: Monduzzi Editore, 1999: 153–155.
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Inner Ear Extension of Vestibular Schwannomas Maurizio Falcioni, MD; Abdelkader Taibah, MD; Di Giuseppe Trapani, MD; Tarek Khrais, FRCS, HSD, MD; Mario Sanna, MD
Objective: Inner ear extension of vestibular schwannomas (VSs) is a rare finding but has important clinical implications. This report reviews the treatment options and presents the experience of the Gruppo Otologico, Piacenza, Italy, in this field. Study Design: Case report and literature review. Methods: Five cases of VSs with inner ear extension were surgically removed. In all of them, the cochlea was partially or completely invaded by the lesion. Results: In 4 cases, the inner ear extension was preoperatively identified on magnetic resonance imaging, and the surgical removal was planned through a transotic approach. In the last case, the cochlear invasion was not detected preoperatively, and the lesion was removed during a second surgery performed to seal a cerebrospinal fluid fistula. Conclusions: VSs with inner ear extension should be distinguished from pure intralabyrinthine schwannomas because of differences in clinical significance. Cochlear involvement is more frequent than vestibular involvement and is often accompanied by a dead ear. Dead ear caused by small VSs should alert the surgeon to the possibility of a cochlear extension. The presence of an intracochlear involvement requires the adoption of an approach that allows control of the cochlear turns, and we found the transotic approach to be the most suitable. Undetected cochlear extensions that are left in place may grow with time. Key words: Vestibular schwannoma, vestibule, cochlea, inner ear, labyrinth. Laryngoscope, 113:1605–1608, 2003
INTRODUCTION Until the late 1980s, schwannomas confined to the labyrinth were reported almost exclusively as intraoperative or postmortem finding. The situation changed after the introduction of magnetic resonance imaging (MRI), when the preoperative discovery of intralabyrinthine schwannomas (ISs) became more frequent. In our opinion, these lesions should be distinguished from labyrinthine From the Gruppo Otologico, Piacenza, Italy. This work was supported by a grant from A.S.A.B. (Associazione Studio Aggiornamento Basicranio). Editor’s Note: This Manuscript was accepted for publication May 7, 2003. Send Correspondence to Maurizio Falcioni, MD, Gruppo Otologico, Via Emmanueli 42, 29100 Piacenza, Italy. E-mail: maurizio.falcioni@ gruppootologico.it
Laryngoscope 113: September 2003
involvement by vestibular schwannomas (VSs) because of the different clinical implications. The following study reports 5 cases of VSs with inner ear invasion surgically treated at the Gruppo Otologico, Piacenza, Italy. A summary of the main features of the five cases is reported in Table I.
CASE REPORTS Case 1 A 24-year-old man reported a sudden right-sided hearing loss (HL) and tinnitus for 2 years, in the absence of any vestibular complaints. Audiometry revealed the presence of right-sided anacusis. MRI showed a right-sided internal auditory canal (IAC) neoformation that invaded the basal turn of the cochlea. Cochlear extension was not mentioned on the radiologic report. Surgical removal was accomplished through a transotic (TO) approach. The patient was discharged after 5 days with normal facial function. At follow-up after 1 year, the MRI did not show any tumor recurrence.
Case 2 A 49-year-old woman reported a progressive left-sided HL over 13 years, accompanied by occasional tinnitus and vertigo. Audiometry revealed the presence of left-sided dead ear. MRI showed a cerebellopontine angle neoformation (size 1 cm) with invasion of the cochlea. Cochlear extension was not mentioned on the radiologic report. The tumor was removed through a TO approach. The patient was hospitalized for 6 days and discharged with a facial nerve (FN) dysfunction (grade III according to the House-Brackmann scale). At the last follow-up, 1 year after surgery, the FN function had recovered to grade II.
Case 3 A 26-year-old woman reported a progressive right-sided HL and tinnitus over 1 year. She did not experience any vestibular disturbances. Audiometry revealed the presence of right-sided dead ear. MRI revealed an intracanalicular neoformation. No inner ear extension was mentioned on the radiologic reports of the two MRI scans that had been done elsewhere. The tumor was removed through a translabyrinthine approach (TLA). After 3 days, the patient experienced a rhino-liquorrhea. Reevaluation of the preoperative MRI showed the presence of tumoral extension into the basal turn of the cochlea (Fig. 1). During the revision surgery for closure of the cerebrospinal fluid fistula, the cochlea was drilled, and the residual tumor was removed. The patient was hospitalized for 9 days and discharged with a FN palsy. One
Falcioni et al: Extension of Vestibular Schwannomas
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TABLE I. Patient Features. Patient
Symptoms
Hearing
Symptoms Duration
Inner ear Involvement
IAC/CPA Involvement
1 2
HL, tinnitus HL, tinnitus, vertigo HL, tinnitus
Dead ear Dead ear
2 years 13 years
Basal turn Cochlea
Dead ear
1 year
3 4 5
HL, tinnitus, Dead ear vertigo HL, Dead ear unsteadiness
24 years 5 years
Middle Ear Involvement
Radiological Report
Preoperative Detection
Approach
IAC CPA (1 cm)
NO NO
No IE involvement No IE involvement
YES YES
TO TO
Basal turn
IAC
NO
NO
All
CPA (3 cm)
YES
No IE involvement (2 MRI) No IE involvement
YES
Cochlea
IAC
NO
No IE involvement
YES
TLA and revision TO TO
IAC ⫽ internal auditory canal; CPA ⫽ cerebellopontine angle; HL ⫽ hearing loss; IE ⫽ inner ear; TO ⫽ transotic approach; TLA ⫽ translabyrinthine approach;MRI ⫽ magnetic resonance imaging.
year later, the MRI showed no recurrence, and the FN function had recovered to a grade III.
Case 4 A 48-year-old woman reported a left-sided tinnitus over 24 years accompanied by a left-sided progressive HL over 13 years. She also experienced one episode of vertigo. Audiometry revealed the presence of left-sided dead ear. The MRI showed a 3 cm cerebellopontine angle neoformation extending to the IAC, all the inner ear, as well as the geniculate ganglion (Fig. 2). Both the inner ear and geniculate ganglion involvement were not mentioned on the radiologic report. The computed tomography (CT) scan showed an IAC enlargement and the presence of soft tissue in middle ear near the round window (Fig. 3). The geniculate fossa was enlarged as well. Tumor removal was planned through a TO approach. During the surgery, two different lesions were disclosed, originating respectively from the VIII and VII cranial nerve. The tumor filled all the inner ear protruding into the middle ear cavity through the round window. It was not possible to locate the central stump of the FN. The patient was hospitalized for 6 days and discharged with a total palsy of the VII cranial nerve. Two months later, the patient underwent hypoglosso-facial anastomosis. At the first follow-up, 3 months after the last surgery, the FN function was still grade VI.
Case 5 A 54-year-old man reported a right-sided HL and unsteadiness over 5 years. Audiometry revealed the presence of rightsided dead ear. The MRI showed an IAC lesion involving all the cochlea turns (Fig. 4). Surgical removal was planned through a TO approach. The patient was hospitalized for 4 days and discharged with a normal FN function (grade I). Because he was operated on only few months ago, no follow-up is presently available.
DISCUSSION Histologically, VSs develops in the myelinated part of the VIII cranial nerve, often in the IAC. However, Schwann cells are also present in the modiolus, close to the spiral ganglia1, so schwannomas theoretically may arise in this area. The first report of an IS is attributed to Mayer, in 1917.2 It was discovered at autopsy in a patient affected by neurofibromatosis. Since then, a few cases have been reported as postmortem or intraoperative findings during surgery for Me´ nie`re’s disease.3 The first preoperative raLaryngoscope 113: September 2003
1606
diologic diagnosis of an intracochlear schwannoma was reported by Karlan et al.4 in 1972, through a polytomography demonstrating nonvisualization of the basal turn of the cochlea. In 1994, Doyle and Brackmann5 reported the first series of preoperatively diagnosed ISs through MRI. Currently, refinements in the MRI technique allow the differentiation of lesions developing in the inner ear, including small tumors.6 The increased frequency of reporting ISs during the last years has coincided with the development of the MRI. In some articles, pure ISs have been listed together with labyrinthine involvement by VSs.5,7,8 In agreement with Zbar et al.9, we think that the two lesions should be distinguished from each other because of the different clinical implications and, probably, the different site of origin. In fact, although it is not possible to definitively identify the origin of a schwannoma with IAC and inner ear involvement,10 the hypothesis of a progressive involvement of the labyrinth during the growth of a VS seems to be more reasonable. This is supported by the fact that cochlear involvement is more frequent than vestibular involvement. This difference can be explained by the presence of the weakest part of the fundus, the cribriform area, between the IAC and the cochlea.11 All our cases showed involvement of the cochlea. Two of the smallest tumors (cases 1 and 3) had a minimal inner ear component, confined to the basal turn of the cochlea, as if discovered at the beginning of the invasion. If the tumor’s origin was in the cochlea, it is difficult to understand why such a tumor should first erode the cribriform area before growing along the way of least resistance offered by the cochlear turns. However, it seems reasonable to suppose the tumor originated from the cochlear nerve.12 This is in agreement with our surgical finding in which, in all three small tumors, there was a clear involvement of the cochlear nerve. In the two remaining lesions, the IAC was completely filled by the lesion, and it was not possible to establish the nerve of the origin. In rare cases, the tumor involving the inner ear can have further growth into the middle ear, through the oval window or the round window. Because of the natural barrier represented by the footplate, the round window Falcioni et al: Extension of Vestibular Schwannomas
www.medicsindex.com
route is more probable and has been reported more frequently in literature.11,13,14 In one of our patients, the tumor completely filled the inner ear, with a small component protruding into the middle ear cleft through the round window. This extension was visible on MRI and was further confirmed by a CT scan. As already reported, CT scan is useful as a complementary evaluation for schwannomas involving the middle ear, allowing a clear definition of the lesion’s extent and its relationship with the surrounding structures.11 HL, tinnitus, and vertigo are the symptoms usually reported in presence of an IS. It seems that vertigo is related only to the involvement of the posterior labyrinth.5 This may not be the case in VSs with inner ear extension because the symptomatology is also related to the retrocochlear component of the tumor. All of our five cases presented with HL that progressed to anacusis at the time of diagnosis. Vertigo was reported at the beginning of the symptoms by two patients. Dead ear seems to be particularly common in cases of VSs with cochlear involvement.5 As a consequence, the contemporary presence of a dead ear and a VS should prompt the surgeon to carefully evaluate the MRI to detect any lateral extension into the cochlea. Although toxic and metabolic theories have also been proposed, HL in these patients seems to be related to the direct cochlear invasion.15 Labyrinthine invasion is clearly visible on MRI as an enhanced mass lateral to the IAC fundus after gadolinium infusion or as a lack of inner ear fluid in the fast spin echo sequences. However, particularly in cases with limited inner ear involvement, this component of the lesion can be overlooked with a nonaccurate scan evaluation. In all our cases, the inner ear extension was not pointed out in the radiologic report. All the scans had been carried out in other centers, probably without adequate experience in petrous bone and cerebellopontine angle (CPA) lesions, and those incomplete reports could have been of particular significance when planning the surgical removal. In four cases, the labyrinthine component was identified by the physicians of Gruppo Otologico during office scan evaluation, but in one patient, the cochlear extension escaped this reassessment (case 3). From a clinical point of view, management of pure IS depends only on symptomatology, in particular the presence of vertigo. If no disabling vertigo is present, the tumor can be radiologically monitored.8 On the contrary, VSs involving the inner ear should be treated according to the IAC/CPA extension, and the patient’s age and wishes. In both instances, no hearing preservation procedure is feasible. The only pure IS patient that presented to our center has been conservatively treated and is being radiologically monitored. All five cases of VSs with inner ear extension presented in this series have been surgically treated. In the four cases in which the inner ear involvement has been preoperatively detected, the removal was planned through a TO approach.16,17 The last case was originally treated by means of a TLA, and the tumor remnants inside the cochlea were discovered during reevaluation of the preoperative scan because of the development of a rhinoliquorrea. A revision surgery was then planned, allowing removal of the residual lesion and cloLaryngoscope 113: September 2003
Fig. 1. Magnetic resonance imaging, axial view, patient 3. The scan shows an internal auditory canal lesion with an extension to the basal turn of the cochlea.
sure of the cerebrospinal fluid fistula. Green and McKenzie7 reported two cases in which a VS with undetected cochlear extension was treated with a TLA, leaving the inner ear component of the tumor. One patient required a revision surgery, whereas the other did not show any tumor growth on serial MRI. The classic TLA allows opening and control of the vestibule and semicircular canal while the cochlea remains inaccessible. In contrast, in the TO approach, the external and middle ear are removed, the external auditory canal is closed as a blind sac, and the cochlea is drilled out. Although this approach is more time consuming, it allows a direct control of any tumor extension inside the cochlea. As a consequence, in the presence of an intralabyrinthine extension of a VS, the TLA can be adopted only when the intralabyrinthine component is limited to the vestibule and the semicircular canals, whereas involvement of the cochlea requires management through a TO approach. The retrosigmoid approach, not allowing access to the inner ear, is contrain-
Fig. 2. Magnetic resonance imaging, axial view, patient 4. A large lesion involving the cerebellopontine angle and internal auditory canal. Enhancement of the cochlea, vestibule, and lateral semicircular canal is also clearly visible.
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Fig. 3. Computed tomograph, coronal view, patient 4. The tumor protrudes from the round window, partially occupying the middle ear cleft.
dicated in the presence of intralabyrinthine tumoral extension. Takizawa et al.18 reported two cases of recurrence after a retrosigmoid approach in patients affected by VSs with intralabyrinthine extensions. Both recurrences occurred mainly in the extradural space. The middle cranial fossa approach theoretically can offer a good exposure of all the vestibule and the turns of the cochlea. However, because complete tumor removal in this pathology requires the sacrifice of hearing, use of such a procedure, which was originally meant to preserve hearing, does not make sense.
CONCLUSIONS Currently, inner ear involvement by VSs is more frequently reported because of the use of high-resolution MRI. In our opinion, VSs with labyrinthine extension should be distinguished from pure ISs because of the different clinical significance and, probably, the different
Fig. 4. Magnetic resonance imaging, axial view, patient 5. The fundus of the internal auditory canal is filled by a lesion extending to the basal turn of the cochlea.
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origin. According to our data, involvement of the cochlea is more frequent than vestibular involvement and is often accompanied by a dead ear. Cochlear invasion by a VS should always be looked for on the MRI, especially in presence of a dead ear, and, because such extensions could be missed by radiologists, the surgeon should personally evaluate the MRI for their presence. The presence of an intracochlear tumoral extension requires the adoption of an approach allowing direct control of the cochlear turns. Because it is impossible to preserve any hearing, the TO approach seems to be the most appropriate procedure. Undetected cochlear extensions left in place during surgery may grow with time and require a revision surgery. Theoretically, because of the frequent anacusis present in these patients, this growth may go on asymptomatically until the tumor reaches considerable size.
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