Recent = Trends in=20 the Management of Acoustic Neuroma

Basant = K Misra,=20 Head of the=20 Department of Neurosurgery & Gamma Knife = Surgery,=20 P D Hinduja National Hospital & Medical Research Centre, Mumbai

Abstract=20

Objective=20 : To analyse the changes = that have=20 taken place in the treatment =20 strategy of Acoustic Neuroma in the author=92s practice as well = as=20 patient=92s outcome expectations over the years, subsequent to = radiosurgery and=20 observation competing as valid options today along with microsurgery.=20

Material=20 & Method: The observations are based on the surgical experience of = 419 cases=20 of AN operated by the author since 1987, 354 of which were operated by=20 microsurgery and 76 by GK Radiosurgery, (11 of these were previously = operated by=20 the author). The series = is analyzed=20 in the three phases of 1987-92 (Initial experience), 1993-99 (Surgeon = oriented=20 phase), and 2000 onwards (Patient oriented phase).

Results &=20 Discussion: In the initial experience (1987-92) the effort was on = preservation=20 of life, eliminating major complications and anatomic preservation of=20 7^th and 8^th cranial nerves. In the surgeon oriented phase = (1993-99),=20 the theme was total excision of the tumour and preservation of facial = function=20 and hearing. The patient = oriented=20 phase (2000 onwards) or phase of maturation was all about functional=20 preservation and quality of life. =20 Total excision though aimed at was not pursued at any cost. The = most=20 frequent postoperative complaints of today, dizzy spells and tinnitus, = were=20 dismissed earlier as nothing significant. =20 In the last 100 consecutive cases operated by microsurgery 86% = were large=20 tumours (>3cm). The total excision rate was 88%. The facial nerve=20 preservation rate was 94% and was grade III or better in 88% cases. The facial function was grade = I in 100%=20 of small (<2cm) tumours. = In the=20 whole microsurgery series = the=20 operative mortality was 2.8% and no mortality in last 100 cases = (0%). The dose of Gamma Knife radiosurgery was = between 12=20 =96 13 Gy to the 50% isodose. = In the=20 Gamma Knife cases, 2 had = to be=20 operated microsurgically because of failure of control by Gamma Knife = . Two patients developed = transient facial=20 paresis following Gamma Knife. =20 Choosing the right modality, helps in optimizing outcome and = improves=20 patient=92s satisfaction.

Key words : = acoustic,=20 microsurgery, radiosurgery, =20 observation, treatment.

Introduction: The = development of=20 acoustic neuroma (AN) surgery parallels the history and progress in the = field of=20 neurosurgery¹¹ = Thus it=20 is but natural that the present day trend of minimally invasiveness = should also=20 be the major influence in decision making in the management of a patient = with=20 AN. This concept of = minimally=20 invasiveness in not new however. = Hippocrates=92 = (460 B.C.)=20 principle of =91Primum Non Nocere=92 =91first of all do not harm=92 is = as old as the=20 history of medicine. = The=20 re-emphasization of =91patient=92s interest=92 first, =91evidence based = medicine=92,=20 became necessary as it became obvious that the medicine is becoming = technology=20 and doctor oriented and hence the question of the natural history of a=20 particular disease vis-=E0-vis the treatment =20 offered. The = controversy of=20 treating incidental aneurysm and intracanalicular acoustic stem from = this=20 concern¹⁵. In this presentation an attempt has been made to = analyze=20 the changes that have taken place in the treatment strategy of AN in the = authors=20 practice over the years. =20

Material=20 & Methods : An=20 analysis of 641 cases of cerebellopontine angle lesions operated by the = author=20 since 1987 yielded 419 cases of AN. =20 The next common tumour was meningioma (76 cases). Of the 419 cases of AN, = microsurgery was=20 the main option and 354 cases have been thus managed. GKR was the treatment = option for=20 76 cases, of which 11 cases were = previously operated by the author. Though not included in = the series,=20 there were a number of cases of AN where only observation without = intervention=20 was carried out. All = cases of=20 microsurgery were operated by a retromastoid retrosigmoid route. This is the only route, which = is not=20 only adequate for all sizes of tumours but also suitable for = preservation of=20 facial function and hearing ^{5-10,13, 17}. No doubt, enough literature is = available=20 now to document translabyrynthine and middle fossa approaches as = excellent means=20 of tackling selected tumours³. Though the author has = used both=20 these approaches extensively for other skull base lesions, it has not = been=20 necessary to change the strategy of retrosigmoid route for AN over the=20 years¹⁰. =20

Results : A = consecutive series=20 of 100 cases of AN managed microsurgically by the author was published = in=20 1993⁶. The = various=20 changes in treatment strategy, =20 since 1987 was analyzed by comparing the series of =9193 to the = present=20 data comprising of last 100 consecutive case operated by microsurgery by = the=20 author. While the = only=20 treatment option available in 93 was microsurgery, the various option = available=20 today are microsurgery, radiosurgery and just observation.=20

Microsurgery : = The=20 authors indication of = microsurgery=20 as the first option today are :

all tumours = >2.5cm=20 in the largest diameter
any patient = with=20 brainstem dysfunction or significant mass effect=20
young = patient=20 (<40yr) with any tumour size
tumors with=20 significant cystic components

Though there = has been=20 some changes in the technique employed, the basic retromastoid = retrosigmoid=20 approach has not changed over the years ^6-10. Today the author employs = a supine=20 position with head turned to the contralateral side as opposed to = lateral=20 position and a craniotomy as opposed to craniectomy earlier.

The=20 tumour size was smaller in 2005 compared to 1993 indicating earlier = detection=20 (Table I).

While=20 facial nerve preservation rate was higher at 94% in 2005 compared to 72% = in 1993=20 the total excision rate was lower (88% compared to 94% in 1993). However, there are a few = pertinent=20 points of note :

total = excision was=20 determined by postoperative contrast MRI in most cases in 2005 as = opposed to=20 contrast CT in 1993. =20
the emphasis = was on=20 good facial function and hence a thin sliver of tumour over the facial = nerve,=20 which showed as enhancing tumour =20 on post op MRI (often not requiring any treatment) was accepted = as=20 better for the patient though classified as subtotal excisim.

A=20 retrospecitive analysis of the facial function in the last consecutive = 100 cases=20 operated by the author microsurgically showed preoperative facial palsy = on=20 3. Anatomic continuity at = surgery=20 was maintained in 94 (Table II). = The post operative detailed facial function data was not = available in 7=20 cases. In the 93 cases where data was available post op. facial function = was=20 grade I-II in 63% and grade III in 25% and grade IV worse in 12% (Table=20 III). Thus in 88% of = cases the=20 facial function was grade III or better. Postoperative facial function = was=20 directly related to the size of the tumour. While 88% of cases of large = tumours had=20 grade III or better facial function it was 89% in medium tumour and 100% = in=20 small tumours. In fact = all the=20 cases with small tumours had grade I facial function postoperatively = (Table=20 IV). Detailed = evaluation of=20 the hearing status is in progress. =20 Though hearing preservation and to what degree is = unpredictable, the author has been able to = preserve=20 useful hearing after microsurgery even for large tumors⁴ has = been the=20 experience of some select surgeons^5,9.

Radiosurgery : Improvement = in=20 imaging techniques have led to earlier diagnosis of AN. The small size of AN have made = these=20 tumours amenable to GKR. Reports of long term control of tumour with = good=20 cranial nerve function has led to increased enthusiasm for its use in = selected=20 patients ^1,2,4,14. =20 Facial nerve function preservation rates have been superior or = comparable=20 to the best results of microsurgical series. The earlier report of = increased=20 cranial nerve dysfunction has reduced significantly with reduction of = tumour=20 dose ⁴. The = concern,=20 however, is the long term control with this lower dosage. The other major = concern has=20 been the risk of malignant degeneration following radiosurgery. However, till date there is no = proof to=20 suggest of any realistic risk of malignancy following GK = Radiosurgery. Today 12-14Gy is = prescribed to 50%=20 isodose in Gamma Knife =20 Radiosurgery. The = reported=20 long term control rate is between 93% - 97%^2,4,14. Recently, there has been = reports of even=20 improved hearing after GK Radiosurgery ^2,12. The hearing preservation is = however=20 unpredictable. The author = has=20 treated 76 cases of Acoustic Neuroma =20 by GK Radiosurgery since 1997. Two of these cases have = undergone=20 microsurgery following continued growth. =20 Two patient developed temporary Gr II facial paresis which = cleared after=20 three months. = Detailed=20 evaluation of their hearing status is in progress. Another complain following GKR = in some=20 patients have been =91a sensation of pulling in the face=92 though no = obvious=20 hypoesthesia or paralysis can be objectively demonstrated. In patients who presented with = giddiness=20 and imbalance, the symptoms often get worse after GK and in the = author=92s=20 experience it takes longer for these symptoms to settle down in = radiosurgery=20 than in microsurgery. = Presently=20 author=92s indications for Radiosurgery are patients with tumours of = 2.5cm or less=20 in maximum diameter and

With high = medical risk=20
Elderly = patient=20
Recurrent or = residual=20 tumour showing growth.

Of=20 course, some younger patients with tumours less than 2.5cm have been = treated by=20 GK, though they have been offered microsurgery as the first choice.

Observation : Studies on = natural=20 history of AN have shown = that there=20 are some tumours which do not grow and remain static over a long period = of=20 time^13,15. = Some=20 patients, thus could merit just follow up, especially when picked up=20 incidentally. It is = mandatory,=20 however, that such patients are available for regular follow up. Because of the low = socio-economic status=20 of many patients in our country, poor follow up because of long = distances=20 patient has to travel, one is weary of advising =91Observation=92. Though not included in = this series=20 of 419 cases, the author has occasionally advised follow up in some and = in some=20 others only a ventriculoperitoneal shunt has been done. Mostly these have been elderly = patients=20 who have had a long history of auditory symptoms and static tumours,=20 incidentally picked up tumour because of imaging for some other reason = or when=20 they have presented with normal pressure hydrocephalus. =

One of=20 the most controversial and difficult decisions is the management of=20 intracanalicular AN (ICAN)¹⁵. =20 Whether to treat? When to treat? Whether microsurgery or = radiosurgery?=20 Our present policy of dealing ICAN is as follows : =

Incidental = ICAN are=20 observed
ICAN with = significant=20 vestibular dysfunction are managed microsurgically as relief of = giddiness and=20 imbalance is faster and better by microsurgery than GKR.

Evidence=20 for recommending any treatment, be it microsurgery or GKR, for an = asymptomatic=20 patient with ICAN to prevent hearing loss is lacking, because the = natural=20 history of such lesions as far as hearing is concerned is probably = better than=20 any intervention. = However, when the=20 patient of ICAN has progressive hearing loss intervention may be advised = provided the treatment = can arrest=20 or improve hearing. Some = reports of=20 improvement of hearing by both microsurgery and GKR are available. In the author=92s small series = of ICAN the=20 progression of hearing loss has been arrested and hearing preserved but=20 improvement has not been observed. =20 If refinement of planning in GK results in hearing improvement = more=20 consistently then it could be recommended. As of now, the author would = advise=20 observation for a patient of ICAN with normal hearing and microsurgery = for a=20 patient of ICAN with = progressive=20 hearing loss or = significant=20 vestibular dysfunction (Fig. 1).

Finally, the = management=20 mortality in the author=92s series from 1987 is shown in figure 2. While we have achieved a 0% = mortality in=20 the last 100cases which is the way it should be, the earlier losses of = life=20 cannot be forgotten and is a grim reminder of the fact that this is a major procedure = and=20 cannot be treated lightly.

Conclusion : Acoustic = Neuroma of all sizes can be operated = by the=20 retrosigmoid approach with gratifying results. Both facial function and = hearing=20 can be preserved after microsurgery even in large tumours, hence no = effort=20 should be spared to save these nerves. However, there is no = doubt that=20 some patients are better served with GKR and yet some others by no = intervention=20 at all. Equally important = to=20 remember that microsurgery for AN is a major procedure and even a = seemingly=20 innocuous few drops of postop CSF rhinorrhoea can kill a patient.

In=20 summary, the approach for a given patient should be patient oriented and = not=20 surgeon oriented. = Furthermore=20 meticulous attention to minute details of each aspect of microsurgery is = essential to avoid catastrophe. = The=20 indications of GKR and microsurgery are still evolving. Selection of the appropriate = option, by=20 a surgeon with ample experience, though not easy, is crucial to an optimal = outcome.

References=20

1. =20 Flickinger=20 JC, Kondziolka D, Niranjan A, Lunsford LD. Results of Acoustic Neuroma=20 Radiosurgery : An analysis of 5 years experience using current methods. = J=20 Neurosurg 94: 1-6, 2001.

2. =20 Gabert K, = Regis J,=20 Delsanti C, et al. = Preserving=20 hearing function after Gamma Knife Radiosurgery for Unilateral = Vestibular=20 Schwannoma =96 Neurochirugie 50, 350 =96 7, 2004.

3. =20 Haddad GF, = Al-Mefty O :=20 The road less traveled : Trans-temporal access to CPA. Clin Neurosurg, 41 : 150-67,=20 1994.

4. =20 Lunsford LD, = Niranjan A,=20 Flickingsr JL et al. = Radiosurgery=20 of Vestibular Schwannoma: Summary of experience in 829 cases. JNS 102=20 (Suppl.):195-9, 2005.

5. =20 Mathies C, = Samii M,=20 Vestibular and auditory function: =20 Options in large T3 and T4 tumour. =20 Neurochirurgic 48:461-70, 2002

6. =20 Misra=20 BK, Rout D, Bhiladvala DB : Current Status of Acoustic Neuroma Surgery. In Abstracts. = Neuroconf, Madras=20 1993.

7. =20 Misra=20 BK, Rout D, Bhiladvala DB, Radhakrishnan V. Spontaneous haemorrhage in = Acoustic=20 Neuromas. Br. J = Neurosurgery 9 : 219-211, = 1995.

8. =20 Misra BK, = Microsurgical=20 Approach to Cerebello pontine angle tumour. In 11^th ICNS = 363-369,=20 Monduzzi Editors, 1997.

9. =20 Misra BK, = Management of=20 Acoustic Neuroma =96 An overview in Brain tumour surgery Ed T Kanno, = Japan Brain=20 Tumour Society, 2000, 133-138.

10. Misra BK, Changing Trends in the = management of=20 acoustic neuroma. = Progress in=20 Clinical Neurosciences 18: 34-40, 2003

11. Moskowitz N, = Long DM,=20 Acoustic Neuromas : Historical Review of a century of operative series. = Neurosurgery Quarterly, 1:2-18, = 1991

12. Niranjan A, = Lunsford D,=20 Flickinger JC, et al. Can = hearing=20 improve after acoustic tumour radiosurgery? Neurosurg Clin N Am 10: = 305-316,=20 1999. =

13. Ojemann RG : = Management=20 of Acoustic Neuroma : = Clinic=20 Neurosurgery, 40 : 498-535, 1993.

14. Prasad D, = Steiner M,=20 Steiner L, Gamma Surgery for vestibular schwannoma. J Neurosurg 92: = 745-759,=20 2000.

15. Raut VV, Walsh = RM, Bath=20 AP, et al. Clin-Otolaryng = Allied=20 Sci.29:505-14,2004.

16. Regis J, = Pellet W,=20 Delsanti C, et al. = Functional=20 outcome after Gamma Knife surgery or Microsurgery for Vestibular=20 Schwannomas. J.=20 Neurosurg.97:1091-100, 2002.

17. Yasargil MG, = Fox JL :=20 The microsurgical approach to Acoustic Neuroma. Surg Neurol 2 : 393-398, = 1974.=20

Table I=20