Acta Oto-Laryngologica
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method Jin Kanzaki, Kaoru Ogawa, Toshiaki O-uchi, Ryuzo Shiobara & Shigeo Toya To cite this article: Jin Kanzaki, Kaoru Ogawa, Toshiaki O-uchi, Ryuzo Shiobara & Shigeo Toya (1991) Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method, Acta Oto-Laryngologica, 111:sup487, 22-29, DOI: 10.3109/00016489109130441 To link to this article: http://dx.doi.org/10.3109/00016489109130441
Published online: 08 Jul 2009.
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Date: 03 April 2016, At: 04:39
Acta Otolaryngol (Stockh) 1991; Suppl. 487: 22-29
’
Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method JIN KANZAKI,’ KAORU OGAWA,’ TOSHIAKI 0-UCHI’ RYUZO SHIOBARA,’ and SHIGEO TOYA’ From the ‘Department of Otolaryngology and ’Department of Neurosurgery, School of Medicine, Keio University, Tokyo, Japan
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Kanzaki J, Ogawa K, 0-Uchi T, Shiobara R, Toya S. Hearing preservation in acoustic neuroma surgery by the extended middle cranial fossa method. Acta Otolaryngol (Stockh) 1991; Suppl 487: 22-29. The results of attempted hearing preservation were investigated in 160 cases of acoustic neuroma surgery carried out by a team of otologists and neurosurgeons at Keio University Hospital during a 14-year period from 1976 to 1989. Surgery was carried out by the middle cranial fossa (MCF) approach in the earlier cases and by the extended middle cranial fossa (EMCF) approach in the more recent cases. Measurable postoperative hearing was preserved in 20 of the 160 cases. Preoperatively, 22 cases had tumors of 20 mm or smaller in diameter, hearing levels (HL) of 50 dB or lower, and speech discrimination scores (SDS) of 50% or higher; 8 (36%) met these conditions postoperatively. Among those cases with hearing preserved postoperatively, hearing was unchanged from the preoperative level in 9 cases and changed in 11 cases. Total tumor removal was achieved in 19 cases. In one case, part of the tumor was left in order to preserve hearing, but MRI and CT have revealed no change in hearing or tumor enlargement to date, at 4 1/2 years after surgery. Hearing was preserved but progressively deteriorated postoperatively in one case in which the tumor was believed to have been totally removed but there was recurrence and in another case of total resection of neurofibromatosis 11. Postoperatively, there were increased incidences of absence of the stapedius reflex, Type V by BBkksy audiometry, and prolongation of the ITS, disappearance of Wave V, and no response in measurements of the ABR. Key words: hearing preservation, acoustic neuroma surgery, extended middle cranial fossa approach.
INTRODUCTION Until twenty years ago, there was little interest in hearing preservation in acoustic neuroma (AN) surgery. This was due not only to the fact that few patients presented with useful hearing preoperatively but also to the high mortality rates, low rate of total tumor removal, and poor results of attempted preservation of facial nerve function. Advances in diagnostic and surgical techniques, however, have led to lower mortality, as well as higher rates of total tumor removal and preservation of facial nerve function. Hearing preservation has therefore naturally surfaced as the next goal in AN surgery. In recent years, more patients have presented with small tumors of less than 20 mm in diameter and good preoperative hearing. In addition, advances have been made in the intraoperative monitoring of cochlear nerve function. These have led to increased reports of successful hearing preservation. In this paper, we report the results of attempted hearing preservation in cases of AN surgery by the extended middle cranial fossa (EMCF) approach. MATERIAL AND METHODS The results of 160 cases of AN surgery carried out by a team of otologists and neurosurgeons at Keio Universtiy Hospital during a 14-year period from May 1976 to September 1989 were
Hearing preservation in A N surgery
23
investigated. In the 86 cases in the earlier part of the series, hearing preservation was attempted only by the middle cranial fossa (MCF) approach. In the more recent 74 cases, hearing preservation was attempted mainly by the EMCF approach type 111 (1). Those cases with hearing preserved postoperatively were followed over periods ranging from 6 months to 10 years (average: 32 months).
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RESULTS 1) Rate of hearing preservation Of those cases of attempted hearing preservation by the MCF approach among the 86 earlier cases of the series, hearing was preserved in only 5. Compared to the preoperative hearing level (HL) there was no change postoperatively in 4 cases and change in 1 case. In the cases of attempted hearing preservation by the EMCF approach type I11 among the 74 cases in the latter half of the series, hearing was preserved in 15 (22%) cases. Among the 160 cases in the entire series, 22 had tumors of 20 mm in diameter or smaller, HL of 50 dB or lower, and speech discrimination scores of 50% or higher (50/50) preoperatively. Of the 20 cases in which hearing could be preserved postoperatively, the residual hearing deteriorated rapidly postoperatively and the deafness occurred in 2 cases. However, among the 22 cases with 50/50 hearing and tumors of 20mm in diameter or smaller preoperatively, hearing was preserved in 8 (36%) (Table I).
Table I. Pre- and post-operative hearing level and speech discrimination scores in cases with preserved hearing
Group
Sex
Age
Tumor size
Hearing level*
Maximum speech discrimination serve
Approach
Pre-op
Post-op
Pre-op
Post-op
A
1. 2. 3. 4. 5. 6. 7. 8.
M. S. H. M. K. C. H. K. E. S. I. M. S. K.
Y.s.
F M F F F M M F
53 37 52 44 55 37 45 32
IC IC IC IC 30 5 IC 20
MCF MCF MCF MCF EMCFIII EMCFIII EM CF III EMCFIII
17 25 48 72 30 23 25 62
25 30 47 65 40 30 32 65
80 82 68 26 72 92 56 48
80 70 60 20 NT 90 68 NT
B
1. 2. 3. 4. 5.
U. K. M. S. Y. M. M. Y. 0. A.
F F M M M
38 49 23 26 35
16 18 IC 20 IC
EM C F III MCF MCF EMCFIII MCF
20 18 62 12 63
35 53 63 32 97
80 60 90 92 54
50 50 24 60 20
C
1. H. N. 2. K. Y. 3. S. M.
F M F
53 55 58
10 IC 30
MCF MCF EMCFIII
34 62 57
58 88 62
70 22 NT
52 6 40
D
1. Y. H. 2. Y.J.
M M
63 55
IC IC
EMCFIII EMCFIII
30 43
88 83
72 12
NT NT
E
1. Y .M. 2. 0. T.
F M
18 43
5 15
EMCFIII EMCFIII
80 18
77 25
20 78
16 80
*
dB, average in 500 Hz, 1 000 Hz and 2 000 Hz. NT: not tested.
(Oh)
24 J . Kanzaki et al. 2) Postoperative course Cases with hearing preserved often show findings of mixed hearing loss immediately after surgery. This is attributable to conduction disturbance due to leakage of cerebrospinal fluid (CSF) from the mastoid air cells around the internal auditory canal into the tympanic cavity and to the effects of surgical manipulation on nerves and blood vessels. Among the 20 cases in which hearing was preserved postoperatively, follow-up observation was carried out for 6 months or longer (average: 32 months) in all but the 2 cases in which the patients became deaf about one month postoperatively. A change in the conversational range (500 Hz 1 000 Hz + 2000 Hz/3) postoperatively of less than 15 dB was classified as “unchanged” (A group), while that of 15 db or more was classified as “deteriorated.” Only those cases with measurable hearing were classified as “deteriorated” i.e, patients who were deaf were not classified. Those cases with deterioration of hearing were divided into 4 groups according to the postoperative course. In most of the cases, hearing was either unchanged or deteriorated postoperatively but stabilized thereafter. There were 3 cases in which the patient developed severe hearing impairment or deafness postoperatively but in which the HL later recovered to levels that, while less satisfactory than before surgery, were nevertheless measurable. In 2 cases, hearing deteriorated after a considerable interval after surgery. One was a case of neurofibromatosis 2, and the other was a case of recurrence of unilateral AN (Fig. 1, Table 11). Among the 20 cases with hearing preserved postoperatively, there were 12 cases with 50/50 hearing preoperatively; only 8 of these had 50/50 hearing postoperatively. Total removal of the tumor was achieved in 19 of the 20 cases. In one case, a part of the tumor was left intact because intraoperative monitoring revealed deterioration of the electrocochleographic action potentials ( AP) and compound action potentials. At 4 1/2 years after surgery, hearing is stable, and CT and MRI findings reveal no enlargement of the tumor. In another case, the tumor was believed to have been totally removed, but there was recurrence (cyst formation) 2 1/2 years after surgery.
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+
3) Postoperative jndings of BPktsy audiometry, stapedius reflex (SR) test, and auditory brain stem response ( A B R ) audiometry The findings of BekCsy audiometry, SR test, and ABR audiometry at 6 months to 1 year after surgery were examined. Compared to the preoperative findings, these were either almost unchanged or deteriorated. There were hardly any cases of improvement after surgery (Tables 111, IV and V). Postoperatively, there tended to be an increase in the number of cases classified as Jerger type IV by BCktsy audiometry or with absence of the SR. In the ABR test, there were increased incidences of abnormal findings such as prolongation of the interaural differences of wave V (IT5), disappearance of wave V, and complete absence of all waves.
DISCUSSION 1) Increused incidence of small tumors It is known that hearing preservation is difficult in AN surgery when the tumor exceeds 20 mm in diameter (2). The 160 cases in our series were divided into the early period (50 cases), middle period (50 cases), and most recent period (60 cases), and the distribution of cases according to tumor size was investigated. The incidence of tumors of 20 mm in diameter or smaller increased from 24% in the early period, to 42% in the middle period, to 58% in the late period (overall incidence: 42.6%).
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26 J. Kanzaki et al. Table 11. Course of post-operative hearing, pre- and post-operative hearing levels and speech discrimination scores Hearing level/Speech discrimination (dB)/(%)
No
Post-op course
Pre-op
Post-op Short-term
At. final exam
~~
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A. Unchanged B. Deteriorated but thereafter unchanged C . Deteriorated but partly recovered D. Progressively deteriorated E. Deteriorated gradually or after long interval
*
9
40.5/68.2 dB/%
44.2/58.9
4
28.3/71.5
54.3/45.0
3
51.0/41.0
92.0 dB
3
36.5142.0
85.5
2*
49.0149.0
52.0/48.0
1
69.3132.1
81.0/34.0
One case of neurofibromatosis 2 and one case of recurrence.
Table 111. Pre- and post -operative BPkksy audiograms Post-op
Pre-op
Type Type Type Type
I I1 111 IV
Type I
Type I1
Type 111
5 0 0
0 0 0 0
1 0 0 0
1
1
1
1
6
0
1
4
11
1
Total
Type IV 1
Total 7 2
1
Table IV. Pre- and post-operative stapedius refex test findings Post-op
Pre-op
Normal
Elevated threshold
Absent
Total
Normal Elevated threshold Absent
3 0
0 1
3 0
6 1
0
2
3
5
Total
3
3
6
12
2) Postoperative hearing During and immediately after surgery , hearing is liable to be affected by damage to the inner ear or cochlear nerve by surgical manipulation and by disturbances in conduction due to the accumulation of CSF with in the tympanic cavity. These factors should especially be taken into consideration when examining the findings of audiological monitoring.
27
Hearing preservation in A N surgery
Table V. Pre- and post-operative ABR test jndings Post-op
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Pre-op
IT, < 0.2 ms
IT,0.2
IT5 1.0 ms
Loss of wave V
No response
0
1 0
5 0 0
0 0 0 0 0
6
0
1
Total
1
2 4 6 1
1
1
4
14
1
Postoperative changes in hearing are due to disturbance of blood flow to the inner ear and damage to the cochlear nerve during surgical manipulation. Evidence of damage to the cochlear nerve is demonstrated postoperatively by the findings of BCktsy audiometry, SR test, and ABR audiometry. In the cases in which hearing deteriorated postoperatively but later improved, the recovery is believed to be due to improvement in the inner ear damage and the disturbance of intraneural blood flow. According to Kveton et al. ( 6 ) , this hearing loss is caused by a conduction block of the cochlear nerve. We believe that disturbance of the intraneural blood flow is involved in such a conduction block and surmise that disturbance of blood flow to the inner ear is an additional factor. A similar mechanism is believed to be involved in the cases of rapid postoperative hearing deterioration. The fact that hearing remained severely impaired for a time postoperatively but the residual hearing deteriorated rapidly thereafter, leading to deafness, may indicate the rapid progression of the inner ear damage. Group E comprises one case of recurrence and one case of neurofibromatosis 2. Since the tumor is known to invade the nerve in the latter case, the results are an expected outcome. Histological studies have reported that attempts to preserve hearing in cases of unilateral AN may possibly result in tumors that have invaded the cochlear nerve to be left intact (7). However, since no connection has been found between preoperative audiological findings and histological cochlear nerve findings (8), particularly as regards the invasion of the tumor into the nerve, we currently have no way of predicting preoperatively whether invasion has occurred. In those cases in which hearing was preserved postoperatively, the histological findings on the cochlear nerve are not known, so it is necessary to watch out for recurrence through postoperative audiological examinations and by CT an MRI. In the 18 cases excluding those in group E, no recurrence was observed by CT or MRI. In the case of neurofibromatosis 2 in group E, in which hearing deteriorated after an extended postoperative period, no recurrence was observed by MRI, but invasion of the cochlear nerve was suspected. Rosenberg et al. (9) have reported no deterioration of the preserved hearing and have found no recurrence by CT in their cases of unilateral AN. Based on this and other reports, as well as on our own experiences, we feel that in cases with satisfactory preoperative hearing or with hearing loss in the contralateral ear, an effort to preserve hearing should be made after consideration of the tumor size and the intraoperative macroscopic findings on the
28 J . Kanzaki et al. Table VI. Pre- and post-operative classification for hearing preservation according to Gardner (Ref. 10) Gardner classification 1
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2 3 4 5
PTA (dB)
Speech discrim (%)
Pre-op
0-30 31-80 61 -90 91 -max.loss No response
100-70 69- 50 40-5 4- 1 No response
10 4 6 0 0
4 7 2 2
20
20
Post-op
5
cochlear nerve. Meanwhile, in cases of neurofibromatosis 2, hearing should be preserved even if only temporarily.
3 ) Rate of successful hearing preseruation An excellent summary of the literature on hearing preservation after AN surgery is presented in the report by Gardner et al. (10). In order for hearing to be preserved postoperatively, the tumor should be 20mm in diameter or smaller (the preservation rate is even better with tumors of 10mm or smaller); the preoperative hearing level should be 50dB or better; the SDS should be 50% or higher; and the ABR wave V should be identifiable (11). There is as yet no consensus on which surgical approach affords the best results in regard to hearing preservation. One reason for this is that the method of evaluating hearing preservation varies from one investigator to another. Specific methods of evaluation have even been proposed. Table VI shows our results organized according to the method of Gardner et al. (2). In the future, it will be desirable and necessary for different investigators to study hearing preservation by comparative analysis under set conditions and by the same method of evaluation. REFERENCES 1. Kanzaki J, Shiobara R, Toya S. Classification of the extended middle cranial fossa approach. Acta Otolaryngol (Stockh) Suppl 487: 6- 16 (this supplement).
2. Glasscock ME, Hays JW, Josey AF et al. Middle fossa approach for acoustic tumor removal and preservation of hearing. In: Brackmann DE, ed. Neurological surgery of the ear and skull base. New York: Raven Press, 1982: 223-6. 3. Tos M, Thomsen J. The price of preservation of hearing in acoustic neuroma surgery. Ann Otol Rhino1 Laryngol 1982; 91: 240-5. 4. Tos M, Thomsen J. Middle fossa operation and suboccipital operation for removal of acoustic neuromas. Acta Otolaryngol (Stockh) 1988; Suppl 449: 21-2. 5. Thomsen J, Tos M, Hamsen A. Acoustic neuroma surgery:results of translabyrinthine tumour removal in 300 patients. Discussion of choice of approach in relation to overall results and possiblility of hearing preservation. Bnt J Neurosurg 1989; 100: 594-601. 6. Kveton JF, Tarlov EC, Drumheller G et al. Cochlear nerve conduction block: An explanation for spontaneous hearing return after acoustic tumor surgery. Otolaryngol Head Neck Surg 1989; 100: 594-601.
Hearing preservation in A N surgery 7. Neely JG. Is it possible to totally resect an acoustic tumor and conserve hearing? Otolaryngol Head Neck Surg 1984; 92: 162-7. 8. Ylikoski J, Collan Y, Palva T et al. Cochlear nerve in neurilemmomas. Arch Otolaryngol 1978; 104: 679-84. 9. Rosenberg RA, Cohen NL, Ransohoff J. Long-term hearing preservation after acoustic neuroma surgery. Otolaryngol Head Neck Surg 1987; 97: 270-4. 10. Gardner G, Robertson JH. Hearing preservation in unilateral acoustic neuroma surgery. Ann Otol Rhino1 Laryngol 1988; 97: 55-66. 11. Kanzaki J, Ogawa K, Shiobara R et al. Hearing preservation in acoustic neuroma surgery and postoperative audiological findings. Acta Otolaryngol (Stockh) 1989; Suppl 107: 474-8.
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Address for correspondence: J. Kanzaki, Department of Otolaryngology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160, Japan.
29
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method Jin Kanzaki, Kaoru Ogawa, Toshiaki O-uchi, Ryuzo Shiobara & Shigeo Toya To cite this article: Jin Kanzaki, Kaoru Ogawa, Toshiaki O-uchi, Ryuzo Shiobara & Shigeo Toya (1991) Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method, Acta Oto-Laryngologica, 111:sup487, 22-29, DOI: 10.3109/00016489109130441 To link to this article: http://dx.doi.org/10.3109/00016489109130441
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 10
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [Imperial College London Library]
Date: 03 April 2016, At: 04:39
Acta Otolaryngol (Stockh) 1991; Suppl. 487: 22-29
’
Hearing Preservation in Acoustic Neuroma Surgery by the Extended Middle Cranial Fossa Method JIN KANZAKI,’ KAORU OGAWA,’ TOSHIAKI 0-UCHI’ RYUZO SHIOBARA,’ and SHIGEO TOYA’ From the ‘Department of Otolaryngology and ’Department of Neurosurgery, School of Medicine, Keio University, Tokyo, Japan
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Kanzaki J, Ogawa K, 0-Uchi T, Shiobara R, Toya S. Hearing preservation in acoustic neuroma surgery by the extended middle cranial fossa method. Acta Otolaryngol (Stockh) 1991; Suppl 487: 22-29. The results of attempted hearing preservation were investigated in 160 cases of acoustic neuroma surgery carried out by a team of otologists and neurosurgeons at Keio University Hospital during a 14-year period from 1976 to 1989. Surgery was carried out by the middle cranial fossa (MCF) approach in the earlier cases and by the extended middle cranial fossa (EMCF) approach in the more recent cases. Measurable postoperative hearing was preserved in 20 of the 160 cases. Preoperatively, 22 cases had tumors of 20 mm or smaller in diameter, hearing levels (HL) of 50 dB or lower, and speech discrimination scores (SDS) of 50% or higher; 8 (36%) met these conditions postoperatively. Among those cases with hearing preserved postoperatively, hearing was unchanged from the preoperative level in 9 cases and changed in 11 cases. Total tumor removal was achieved in 19 cases. In one case, part of the tumor was left in order to preserve hearing, but MRI and CT have revealed no change in hearing or tumor enlargement to date, at 4 1/2 years after surgery. Hearing was preserved but progressively deteriorated postoperatively in one case in which the tumor was believed to have been totally removed but there was recurrence and in another case of total resection of neurofibromatosis 11. Postoperatively, there were increased incidences of absence of the stapedius reflex, Type V by BBkksy audiometry, and prolongation of the ITS, disappearance of Wave V, and no response in measurements of the ABR. Key words: hearing preservation, acoustic neuroma surgery, extended middle cranial fossa approach.
INTRODUCTION Until twenty years ago, there was little interest in hearing preservation in acoustic neuroma (AN) surgery. This was due not only to the fact that few patients presented with useful hearing preoperatively but also to the high mortality rates, low rate of total tumor removal, and poor results of attempted preservation of facial nerve function. Advances in diagnostic and surgical techniques, however, have led to lower mortality, as well as higher rates of total tumor removal and preservation of facial nerve function. Hearing preservation has therefore naturally surfaced as the next goal in AN surgery. In recent years, more patients have presented with small tumors of less than 20 mm in diameter and good preoperative hearing. In addition, advances have been made in the intraoperative monitoring of cochlear nerve function. These have led to increased reports of successful hearing preservation. In this paper, we report the results of attempted hearing preservation in cases of AN surgery by the extended middle cranial fossa (EMCF) approach. MATERIAL AND METHODS The results of 160 cases of AN surgery carried out by a team of otologists and neurosurgeons at Keio Universtiy Hospital during a 14-year period from May 1976 to September 1989 were
Hearing preservation in A N surgery
23
investigated. In the 86 cases in the earlier part of the series, hearing preservation was attempted only by the middle cranial fossa (MCF) approach. In the more recent 74 cases, hearing preservation was attempted mainly by the EMCF approach type 111 (1). Those cases with hearing preserved postoperatively were followed over periods ranging from 6 months to 10 years (average: 32 months).
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RESULTS 1) Rate of hearing preservation Of those cases of attempted hearing preservation by the MCF approach among the 86 earlier cases of the series, hearing was preserved in only 5. Compared to the preoperative hearing level (HL) there was no change postoperatively in 4 cases and change in 1 case. In the cases of attempted hearing preservation by the EMCF approach type I11 among the 74 cases in the latter half of the series, hearing was preserved in 15 (22%) cases. Among the 160 cases in the entire series, 22 had tumors of 20 mm in diameter or smaller, HL of 50 dB or lower, and speech discrimination scores of 50% or higher (50/50) preoperatively. Of the 20 cases in which hearing could be preserved postoperatively, the residual hearing deteriorated rapidly postoperatively and the deafness occurred in 2 cases. However, among the 22 cases with 50/50 hearing and tumors of 20mm in diameter or smaller preoperatively, hearing was preserved in 8 (36%) (Table I).
Table I. Pre- and post-operative hearing level and speech discrimination scores in cases with preserved hearing
Group
Sex
Age
Tumor size
Hearing level*
Maximum speech discrimination serve
Approach
Pre-op
Post-op
Pre-op
Post-op
A
1. 2. 3. 4. 5. 6. 7. 8.
M. S. H. M. K. C. H. K. E. S. I. M. S. K.
Y.s.
F M F F F M M F
53 37 52 44 55 37 45 32
IC IC IC IC 30 5 IC 20
MCF MCF MCF MCF EMCFIII EMCFIII EM CF III EMCFIII
17 25 48 72 30 23 25 62
25 30 47 65 40 30 32 65
80 82 68 26 72 92 56 48
80 70 60 20 NT 90 68 NT
B
1. 2. 3. 4. 5.
U. K. M. S. Y. M. M. Y. 0. A.
F F M M M
38 49 23 26 35
16 18 IC 20 IC
EM C F III MCF MCF EMCFIII MCF
20 18 62 12 63
35 53 63 32 97
80 60 90 92 54
50 50 24 60 20
C
1. H. N. 2. K. Y. 3. S. M.
F M F
53 55 58
10 IC 30
MCF MCF EMCFIII
34 62 57
58 88 62
70 22 NT
52 6 40
D
1. Y. H. 2. Y.J.
M M
63 55
IC IC
EMCFIII EMCFIII
30 43
88 83
72 12
NT NT
E
1. Y .M. 2. 0. T.
F M
18 43
5 15
EMCFIII EMCFIII
80 18
77 25
20 78
16 80
*
dB, average in 500 Hz, 1 000 Hz and 2 000 Hz. NT: not tested.
(Oh)
24 J . Kanzaki et al. 2) Postoperative course Cases with hearing preserved often show findings of mixed hearing loss immediately after surgery. This is attributable to conduction disturbance due to leakage of cerebrospinal fluid (CSF) from the mastoid air cells around the internal auditory canal into the tympanic cavity and to the effects of surgical manipulation on nerves and blood vessels. Among the 20 cases in which hearing was preserved postoperatively, follow-up observation was carried out for 6 months or longer (average: 32 months) in all but the 2 cases in which the patients became deaf about one month postoperatively. A change in the conversational range (500 Hz 1 000 Hz + 2000 Hz/3) postoperatively of less than 15 dB was classified as “unchanged” (A group), while that of 15 db or more was classified as “deteriorated.” Only those cases with measurable hearing were classified as “deteriorated” i.e, patients who were deaf were not classified. Those cases with deterioration of hearing were divided into 4 groups according to the postoperative course. In most of the cases, hearing was either unchanged or deteriorated postoperatively but stabilized thereafter. There were 3 cases in which the patient developed severe hearing impairment or deafness postoperatively but in which the HL later recovered to levels that, while less satisfactory than before surgery, were nevertheless measurable. In 2 cases, hearing deteriorated after a considerable interval after surgery. One was a case of neurofibromatosis 2, and the other was a case of recurrence of unilateral AN (Fig. 1, Table 11). Among the 20 cases with hearing preserved postoperatively, there were 12 cases with 50/50 hearing preoperatively; only 8 of these had 50/50 hearing postoperatively. Total removal of the tumor was achieved in 19 of the 20 cases. In one case, a part of the tumor was left intact because intraoperative monitoring revealed deterioration of the electrocochleographic action potentials ( AP) and compound action potentials. At 4 1/2 years after surgery, hearing is stable, and CT and MRI findings reveal no enlargement of the tumor. In another case, the tumor was believed to have been totally removed, but there was recurrence (cyst formation) 2 1/2 years after surgery.
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+
3) Postoperative jndings of BPktsy audiometry, stapedius reflex (SR) test, and auditory brain stem response ( A B R ) audiometry The findings of BekCsy audiometry, SR test, and ABR audiometry at 6 months to 1 year after surgery were examined. Compared to the preoperative findings, these were either almost unchanged or deteriorated. There were hardly any cases of improvement after surgery (Tables 111, IV and V). Postoperatively, there tended to be an increase in the number of cases classified as Jerger type IV by BCktsy audiometry or with absence of the SR. In the ABR test, there were increased incidences of abnormal findings such as prolongation of the interaural differences of wave V (IT5), disappearance of wave V, and complete absence of all waves.
DISCUSSION 1) Increused incidence of small tumors It is known that hearing preservation is difficult in AN surgery when the tumor exceeds 20 mm in diameter (2). The 160 cases in our series were divided into the early period (50 cases), middle period (50 cases), and most recent period (60 cases), and the distribution of cases according to tumor size was investigated. The incidence of tumors of 20 mm in diameter or smaller increased from 24% in the early period, to 42% in the middle period, to 58% in the late period (overall incidence: 42.6%).
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26 J. Kanzaki et al. Table 11. Course of post-operative hearing, pre- and post-operative hearing levels and speech discrimination scores Hearing level/Speech discrimination (dB)/(%)
No
Post-op course
Pre-op
Post-op Short-term
At. final exam
~~
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A. Unchanged B. Deteriorated but thereafter unchanged C . Deteriorated but partly recovered D. Progressively deteriorated E. Deteriorated gradually or after long interval
*
9
40.5/68.2 dB/%
44.2/58.9
4
28.3/71.5
54.3/45.0
3
51.0/41.0
92.0 dB
3
36.5142.0
85.5
2*
49.0149.0
52.0/48.0
1
69.3132.1
81.0/34.0
One case of neurofibromatosis 2 and one case of recurrence.
Table 111. Pre- and post -operative BPkksy audiograms Post-op
Pre-op
Type Type Type Type
I I1 111 IV
Type I
Type I1
Type 111
5 0 0
0 0 0 0
1 0 0 0
1
1
1
1
6
0
1
4
11
1
Total
Type IV 1
Total 7 2
1
Table IV. Pre- and post-operative stapedius refex test findings Post-op
Pre-op
Normal
Elevated threshold
Absent
Total
Normal Elevated threshold Absent
3 0
0 1
3 0
6 1
0
2
3
5
Total
3
3
6
12
2) Postoperative hearing During and immediately after surgery , hearing is liable to be affected by damage to the inner ear or cochlear nerve by surgical manipulation and by disturbances in conduction due to the accumulation of CSF with in the tympanic cavity. These factors should especially be taken into consideration when examining the findings of audiological monitoring.
27
Hearing preservation in A N surgery
Table V. Pre- and post-operative ABR test jndings Post-op
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Pre-op
IT, < 0.2 ms
IT,0.2
IT5 1.0 ms
Loss of wave V
No response
0
1 0
5 0 0
0 0 0 0 0
6
0
1
Total
1
2 4 6 1
1
1
4
14
1
Postoperative changes in hearing are due to disturbance of blood flow to the inner ear and damage to the cochlear nerve during surgical manipulation. Evidence of damage to the cochlear nerve is demonstrated postoperatively by the findings of BCktsy audiometry, SR test, and ABR audiometry. In the cases in which hearing deteriorated postoperatively but later improved, the recovery is believed to be due to improvement in the inner ear damage and the disturbance of intraneural blood flow. According to Kveton et al. ( 6 ) , this hearing loss is caused by a conduction block of the cochlear nerve. We believe that disturbance of the intraneural blood flow is involved in such a conduction block and surmise that disturbance of blood flow to the inner ear is an additional factor. A similar mechanism is believed to be involved in the cases of rapid postoperative hearing deterioration. The fact that hearing remained severely impaired for a time postoperatively but the residual hearing deteriorated rapidly thereafter, leading to deafness, may indicate the rapid progression of the inner ear damage. Group E comprises one case of recurrence and one case of neurofibromatosis 2. Since the tumor is known to invade the nerve in the latter case, the results are an expected outcome. Histological studies have reported that attempts to preserve hearing in cases of unilateral AN may possibly result in tumors that have invaded the cochlear nerve to be left intact (7). However, since no connection has been found between preoperative audiological findings and histological cochlear nerve findings (8), particularly as regards the invasion of the tumor into the nerve, we currently have no way of predicting preoperatively whether invasion has occurred. In those cases in which hearing was preserved postoperatively, the histological findings on the cochlear nerve are not known, so it is necessary to watch out for recurrence through postoperative audiological examinations and by CT an MRI. In the 18 cases excluding those in group E, no recurrence was observed by CT or MRI. In the case of neurofibromatosis 2 in group E, in which hearing deteriorated after an extended postoperative period, no recurrence was observed by MRI, but invasion of the cochlear nerve was suspected. Rosenberg et al. (9) have reported no deterioration of the preserved hearing and have found no recurrence by CT in their cases of unilateral AN. Based on this and other reports, as well as on our own experiences, we feel that in cases with satisfactory preoperative hearing or with hearing loss in the contralateral ear, an effort to preserve hearing should be made after consideration of the tumor size and the intraoperative macroscopic findings on the
28 J . Kanzaki et al. Table VI. Pre- and post-operative classification for hearing preservation according to Gardner (Ref. 10) Gardner classification 1
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2 3 4 5
PTA (dB)
Speech discrim (%)
Pre-op
0-30 31-80 61 -90 91 -max.loss No response
100-70 69- 50 40-5 4- 1 No response
10 4 6 0 0
4 7 2 2
20
20
Post-op
5
cochlear nerve. Meanwhile, in cases of neurofibromatosis 2, hearing should be preserved even if only temporarily.
3 ) Rate of successful hearing preseruation An excellent summary of the literature on hearing preservation after AN surgery is presented in the report by Gardner et al. (10). In order for hearing to be preserved postoperatively, the tumor should be 20mm in diameter or smaller (the preservation rate is even better with tumors of 10mm or smaller); the preoperative hearing level should be 50dB or better; the SDS should be 50% or higher; and the ABR wave V should be identifiable (11). There is as yet no consensus on which surgical approach affords the best results in regard to hearing preservation. One reason for this is that the method of evaluating hearing preservation varies from one investigator to another. Specific methods of evaluation have even been proposed. Table VI shows our results organized according to the method of Gardner et al. (2). In the future, it will be desirable and necessary for different investigators to study hearing preservation by comparative analysis under set conditions and by the same method of evaluation. REFERENCES 1. Kanzaki J, Shiobara R, Toya S. Classification of the extended middle cranial fossa approach. Acta Otolaryngol (Stockh) Suppl 487: 6- 16 (this supplement).
2. Glasscock ME, Hays JW, Josey AF et al. Middle fossa approach for acoustic tumor removal and preservation of hearing. In: Brackmann DE, ed. Neurological surgery of the ear and skull base. New York: Raven Press, 1982: 223-6. 3. Tos M, Thomsen J. The price of preservation of hearing in acoustic neuroma surgery. Ann Otol Rhino1 Laryngol 1982; 91: 240-5. 4. Tos M, Thomsen J. Middle fossa operation and suboccipital operation for removal of acoustic neuromas. Acta Otolaryngol (Stockh) 1988; Suppl 449: 21-2. 5. Thomsen J, Tos M, Hamsen A. Acoustic neuroma surgery:results of translabyrinthine tumour removal in 300 patients. Discussion of choice of approach in relation to overall results and possiblility of hearing preservation. Bnt J Neurosurg 1989; 100: 594-601. 6. Kveton JF, Tarlov EC, Drumheller G et al. Cochlear nerve conduction block: An explanation for spontaneous hearing return after acoustic tumor surgery. Otolaryngol Head Neck Surg 1989; 100: 594-601.
Hearing preservation in A N surgery 7. Neely JG. Is it possible to totally resect an acoustic tumor and conserve hearing? Otolaryngol Head Neck Surg 1984; 92: 162-7. 8. Ylikoski J, Collan Y, Palva T et al. Cochlear nerve in neurilemmomas. Arch Otolaryngol 1978; 104: 679-84. 9. Rosenberg RA, Cohen NL, Ransohoff J. Long-term hearing preservation after acoustic neuroma surgery. Otolaryngol Head Neck Surg 1987; 97: 270-4. 10. Gardner G, Robertson JH. Hearing preservation in unilateral acoustic neuroma surgery. Ann Otol Rhino1 Laryngol 1988; 97: 55-66. 11. Kanzaki J, Ogawa K, Shiobara R et al. Hearing preservation in acoustic neuroma surgery and postoperative audiological findings. Acta Otolaryngol (Stockh) 1989; Suppl 107: 474-8.
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Address for correspondence: J. Kanzaki, Department of Otolaryngology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160, Japan.
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