Editorial

Abstract

In this issue, Shirato et al., report on 27 patients with acoustic neuroma managed initially by observation compared with 50 patients managed with stereotactic radiotherapy (1). They address two different questions in this study. The first is whether radiotherapy does anything to control acoustic tumors or simply takes credit for the natural history of these tumors. The second question is whether initial observation is a better initial management strategy than radiotherapy for acoustic neuromas. Observation has been justified as an initial management strategy to preserve hearing as long as possible. Tumors can be quiescent for long periods and therapeutic intervention (especially surgical) can be followed by hearing loss. With a median follow-up of 35 and 31 months in each group respectively (range 4 – 80 months) they found significantly better tumor control in the stereotactic radiotherapy (SRT) group (p , 0.001). Salvage therapy was required in 11/27 (41%) of the observed patients versus 1/50 (2%) of the SRT group. They found that hearing preservation was similar in both groups. Thus with shortterm follow-up, hearing loss from SRT was no greater than that which would be expected from the natural history in untreated tumors. Unless patients are followed closely and salvage radiotherapy is instituted at the earliest sign of progression, hearing preservation should be better with longer follow-up in the initially treated (SRT) patients than in conservatively managed acoustic neuroma patients. There is overwhelming evidence that therapeutic irradiation (radiosurgery and SRT) dramatically changes the natural history of acoustic neuroma by eliminating tumor growth in the vast majority of patients (2–7). It was easy to demonstrate significantly improved control of radiosurgery-treated tumors in a small series of patients with bilateral acoustic neuromas compared to their contralateral matched untreated control tumors (2). The first 5 years of the University of Pittsburgh radiosurgery experience in 162 acoustic neuroma patients was recently reported with 5–10 years of follow-up (3). Tumors were controlled without need for surgical resection in 98% of patients. Other centers have confirmed high local tumor control rates of 85–100% for radiosurgery and SRT. In contrast, observed patients subsequently required therapeutic intervention 41% of the time in Shirato’s series. The advantage of early irradiation over observation should only increase with longer follow-up, but tumor control still needs to be assessed at 10 to 20 years for SRT and radiosurgery as it is now administered with marginal doses of 13 Gy. Many benign tumors such as pituitary adenoma can recur up to 20 years after conventional radiotherapy, so long-term follow-up is important. So far, all of the cases of acoustic neuroma progression after radiosurgery at the University of Pittsburgh have been within 3 years of treatment and tumor control has not decreased with lower doses (3). Other series also support the concept that early radiation treatment of acoustic neuromas is the best way to preserve hearing. Charabi et al. reported that 21 out of 28 conservatively managed patients who were candidates for hearing preservation surgery for their acoustic neuromas (diameter #15 mm, speech discrimination $70%) lost their candidacy for hearing preservation during the observation period (8). Other groups have confirmed high rates of hearing preservation with SRT and conventional radiotherapy (4 –7). Hearing preservation rates for early series of high-dose radiosurgery were in the range of 33–50%. Patients treated with radiosurgery at the University of Pittsburgh during the same time interval as Shirato’s study with improved treatment planning and marginal doses of 13 Gy have similar hearing preservation rates and no facial neuropathy (4). Large, long-term outcome studies of optimally treated acoustic neuroma patients are needed to fully compare SRT and radiosurgery, but there is no question that both treatments are better than observation.