Conservative Management of Acoustic Neuroma

ABSTRACT

Aim of study: To identify those patients with vestibular schwannoma (acoustic neuroma) in whom treatment becomes necessary. Method: Retrospective chart review. Result: A total of 205 patients with small tumors were followed for a mean of 40.8 months. The longest follow-up was 180 months. One hundred and ninety-seven patients had a follow-up of more than 12 months. Eight patients with a follow-up of less than 12 months were excluded from the study. In 136 patients (66.3%) the tumor did not grow. Forty-seven patients (23.9%) showed some evidence of slow growth. Eight of 197 patients (4%) had rapid growth and 6 patients (3%) had radiological evidence of tumor regression. Fifteen patients came to surgery. Five of these showed rapid growth, four developed ataxia in whom tumor growth was slow, three had ataxia without tumor growth, two patients developed brainstem compression, and one patient elected to proceed to surgery, although there were no tumor growth or symptoms. Conclusion: Few patients with small tumors will come to surgery in the short term. Perhaps the majority of patients with such small tumors will not need surgery. Long-term follow-up studies of 20 years or more are required to be come more confident about the natural history of these tumors. This study continues.

Acoustic neuroma (AN), more properly known as vestibular schwannoma (VS),¹ is a benign tumor arising from the eighth cranial nerve in the internal auditory canal (IAC) and cerebellopontine angle (CPA). Before the development of modern imaging techniques, such tumors generally presented late.

The advent of magnetic resonance imaging (MRI) has led to the diagnosis of small and minimally symptomatic tumors, sometimes even as a chance finding. In recent years, watchful waiting with observation of tumor size by repeated MRI (the so-called “wait and scan” option) has become common. Such a policy, carried out for many years, will lead to a better understanding of the natural history of these tumors.

MATERIAL AND METHODS

A retrospective review of patients with small tumors was undertaken from the charts of the senior authors (P.A.F. and N.D.W.B.). Conservative management is considered when the tumor is small or when there are unfavorable patient factors, such as extreme age or serious illness.

Patients with neurofibromatosis type 2 (NFII), previous surgery, or radiation therapy were excluded.

The tumor location was judged to be intracanalicular or intracanalicular with CPA extension. No tumors were solely in the CPA.

The duration of follow-up (time from the first scan to the last scan) and the size of the tumor on first and last scans (the largest measured diameter) were recorded.

Although from a surgical point of view it is the CPA component that is most important, in this study, overall size (i.e., IAC + CPA) was measured. Tumor behavior was judged to be slowly growing (i.e., change < 2mm from last MRI), rapidly growing (> 2 mm from last MRI), stable, or reducing.

RESULTS

Study Group

A total of 205 patients with a radiological diagnosis of AN were managed conservatively between 1989 and 2005. Eight patients with a follow-up of less than 12 months were excluded from the following analysis. One hundred ninety-seven patients have had a follow-up of more than 12 months. Patient ages are given in Table 1, sex distribution in Table 2, and symptomatology in Table 3.

Table 1.

Age at Presentation

Mean	60.84 years
Minimum	26 years
Maximum	89 years

Table 2.

Sex Distribution

Gender	Frequency	Percentage
Male	91	44.4
Female	114	55.6
Total	205	100.0

Table 3.

Summary of Symptoms at Presentation

Symptoms	Frequency	Percentage
Hearing loss	95	46.3
Tinnitus	11	5.4
Vertigo	14	6.8
Hearing loss, tinnitus, vertigo	4	2.0
Asymptomatic	14	6.8
Hearing loss, vertigo	34	16.6
Hearing loss, tinnitus	28	13.7
Ataxia	5	2.4
Total	205	100.0

Tumor Diameter

In 130 patients (63.4%), the tumor was confined to the IAC. In 75 (36.6%), the tumor involved both the IAC and the CPA (Table 4). The mean diameter at diagnosis was about 8.7 mm (range, 2 to 20 mm) and the mean diameter at last follow-up was about 11 mm (range, 3 to 27 mm) (Table 5).

Table 4.

Tumor Location

Site	Frequency	Percentage
IAC, internal auditory canal; CPA, cerebellopontine angle.
IAC	130	63.4
CPA + IAC	75	36.6
Total	205	100.0

Table 5.

Size of Tumor at First and Last MRI

	First MRI	Last MRI
MRI, magnetic resonance imaging.
Mean	8.79 mm	10.90 mm
Minimum	2 mm	3 mm
Maximum	20 mm	27 mm

The study group was divided into 10 subgroups based on the duration of follow-up (12 to 184 months) (Table 6). In 136 patients (66.3%) the tumor did not grow. Forty-seven patients (23.9%) showed some evidence of slow growth. Eight of 197 patients (4.1% had rapid growth and 6 patients (3%) had radiological evidence of tumor regression (Table 7). The majority (179 patients, 90.9%) had no change in their symptoms.

Table 6.

Subclassification of Groups Based on Duration of Follow-Up

Groups	Follow-Up in Months	Frequency	Percent
1	12	33	16.8
2	13–24	46	23.4
3	25–36	23	11.7
4	37–48	25	12.7
5	49–60	30	15.2
6	61–72	21	10.7
7	73–84	6	3.0
8	85–96	1	.5
9	97–108	5	2.5
10	More than 109	7	3.6
Total		197	100.0

Table 7.

Growth Patterns of Tumor during Follow-Up

Pattern of Growth	Frequency	Percentage
Growth	47	23.9
Stable	136	69.0
Rapid growth	8	4.1
Shrunk	6	3.0
Total	197	100.0

Fifteen patients came to surgery, five because of rapid growth; four had slow tumor growth with ataxia and three developed incapacitating ataxia/vertigo although no growth was detected. Two patients developed brainstem compression and one patient elected to proceed to surgery although there were no tumor growth or symptoms (Table 8).

Table 8.

Indications for Groups Who Underwent Surgical Intervention

Indications for Intervention	Number
Rapid growth	5
Ataxia	3
Growth and ataxia	4
Brainstem compression	2
Patient decision	1
Total	15

DISCUSSION

Vestibular schwannomas tend to be slow-growing tumors.^2,3,4,5,6 There are at least 26 published studies on the conservative management of AN.^{7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30} A metanalysis of 21 of these studies (1345 patients) covered the years 1989 to 2003.

The average length of follow-up for all was 3.2 years, ranging from 2.2 to 5 years,³¹ but a much longer period of observation is desirable.

The methods of tumor measurement have varied widely,^{25,29,32,33,34} with some authors believing that volume assessment is essential. However, it is our opinion that tumor assessment should be much simpler.

In a word, a decision about intervention, whether by surgery or radiotherapy, should be made for two reasons only: because of the severity of symptoms, or because of incipient or actual brain stem compression. Any tumor of less than 1.5 cm in the CPA would be very unlikely to produce a brainstem problem, which provides a good rule of thumb when intervention is under consideration.

In this series, 15 patients came to surgery. Four patients showed some tumor growth but developed gross ataxia, 3 patients developed incapacitating ataxia/vertigo without tumor growth, 2 patients developed brainstem compression, and 1 patient elected to proceed to surgery although there was no tumor growth or new symptoms. Finally, 5 patients showed tumor growth without brainstem compression. It might be said that further conservative management of this last group could have been undertaken safely.

All of the patients (100%) who came to surgery have normal facial function (House-Brackmen grade I) as do all the patients who did not have surgery.

This high a figure is rarely reported when more active intervention is undertaken.

All operated patients lost hearing. Of these 15 patients, 11 were judged to have useful hearing but only 3 were within 30 dB of the other ear, making the usefulness of such hearing a doubtful proposition according to the Belfast rule of thumb³⁵ and the Glasgow Benefit plott.³⁶

CONCLUSION

In general, small acoustic tumors neither grow nor produce major symptoms. Many current studies suggest that any treatment may prove to be unnecessary. Long-term studies, perhaps up to 20 years or more, are required to learn more about the natural history of these tumors.