J Korean Med Sci.  2023 Oct;38(40):e332. 10.3346/jkms.2023.38.e332.

Long-Term Outcome of Unilateral Acoustic Neuromas With or Without Hearing Loss: Over 10 Years and Beyond After Gamma Knife Radiosurgery

• Park HR
• Jeong SS
• Kim JH
• Myeong HS
• Park HJ
• Park KH
• Park K
• Yoon BW
• Park S
• Kim JW
• Chung HT
• Kim DG
• Paek SH

• KMID: 2546937
• DOI: http://doi.org/10.3346/jkms.2023.38.e332

Abstract

Background
Since the long-term outcomes of 162 patients who underwent gamma knife radiosurgery (GKS) as an initial or adjuvant treatment for acoustic neuromas (ANs) with unilateral hearing loss were first reported in 1998, there has been no report of a comprehensive analysis of what has changed in GKS practice.
Methods
We performed a retrospective study of the long-term outcomes of 106 patients with unilateral sporadic ANs who underwent GKS as an initial treatment. The mean patient age was 50 years, and the mean initial tumor volume was 3.68 cm 3 (range, 0.10–23.30 cm 3 ). The median marginal tumor dose was 12.5 Gy (range, 8.0–15.0 Gy) and the median follow-up duration was 153 months (range, 120–216 months).
Results
The tumor volume increased in 11 patients (10.4%), remained stationary in 27 (25.5%), and decreased in 68 patients (64.2%). The actuarial 3, 5, 10, and 15-year tumor control rates were 95.3 ± 2.1%, 94.3 ± 2.2%, 87.7 ± 3.2%, and 86.6 ± 3.3%, respectively. The 10-year actuarial tumor control rate was significantly lower in the patients with tumor volumes of ≥ 8 cm 3 (P = 0.010). The rate of maintaining the same Gardner-Robertson scale grade was 28.6%, and that of serviceable hearing was 46.4%. The rates of newly developed facial and trigeminal neuropathy were 2.8% and 4.7%, respectively. The patients who received marginal doses of less than 12 Gy revealed higher tumor control failure rates (P = 0.129) and newly occurred facial or trigeminal neuropathy rates (P = 0.040 and 0.313, respectively).
Conclusion
GKS as an initial treatment for ANs could be helpful in terms of tumor control, the preservation of serviceable hearing, and the prevention of cranial neuropathy. It is recommended to perform GKS as soon as possible not only for tumor control in unilateral ANs with hearing loss but also for hearing preservation in those without hearing loss.

Keyword

Acoustic Neuroma; Radiosurgery; Outcome; Hearing

Figure

• 

  Fig. 1 Cumulative tumor control rates after GKS. (A) Cumulative tumor control rates of all 106 patients. The actuarial 3, 5, 10, and 15-year tumor control rates were 95.3 ± 2.1%, 94.3 ± 2.2%, 87.7 ± 3.2%, and 86.6 ± 3.3%, respectively. (B) Cumulative tumor control rates stratified into 4 groups according to the initial tumor volume. The 10-year actuarial tumor control rates were 92.7 ± 4.1%, 90.0 ± 5.5%, 91.3 ± 5.9%, and 58.3 ± 14.2% in the patient group with initial tumor volumes of < 1 cm3, 1–4 cm3, 4–8 cm3 and ≥ 8 cm3, respectively (P = 0.010). (C) Cumulative tumor control rates stratified into 2 groups according to marginal dose. The 10-year actuarial tumor control rates were 69.2 ± 12.8% and 90.3 ± 3.1% in the patient group with initial marginal doses of < 12 Gy and ≥ 12 Gy, respectively (P = 0.032).GKS = gamma knife radiosurgery.

• 

  Fig. 2 Chronological tumor volume plotting. (A) Tumor volume plotting of the tumor control group. GKS treatment not only prevented tumor growth but also gradually induced tumor volume shrinkage over time after GKS, resulting in an average of about 60% after 150 months compared to 100% of the tumor volume at the time of GKS. In the first 2 years, the tumor was temporarily swollen due to the vascular insult caused by radiation, making it difficult to predict, but after 2 years it was generally consistent with the change in tumor volume. We proposed a formula that could predict the change in tumor volume after the first 2 years after SRS using linear regression analysis. Using this formula, the approximate percent change in tumor volume (y) at t months after SRS could be predicted as shown in this figure: y(t) = 100 − 0.471t. (B) Tumor volume plotting of all 126 patients with imaging follow-up of at least 2 years. As the subjects of this study included patients who had been followed for more than 10 years, bias may occur due to study design. To overcome this, this figure represents tumor volume plotting of all 126 patients who were clinically followed for less than 10 years, if they underwent follow-up image for at least 2 years.GKS = gamma knife radiosurgery, SRS = stereotactic radiosurgery.

• 

  Fig. 3 Case of one patient who underwent FGKS using a frame for AN. We implemented FGKS using a frame before the introduction of ICON™. This case represents one of the patients who underwent FGKS for an AN. An adult patient with a left AN of 3.2 mL underwent FGKS at a marginal dose of 5 Gy per fraction for 4 consecutive days. Afterward, an additional ventriculoperitoneal shunt was required for progressive hydrocephalus. After 52 months, the second stage of FGKS was performed with a marginal dose of 6 Gy per fraction for 5 consecutive days. The ten-month follow-up MRI confirmed that shrinkage occurred along with necrosis inside the tumor.FGKS = fractionated gamma knife radiosurgery, AN = acoustic neuroma, MRI = magnetic resonance imaging, VP = ventriculoperitoneal.

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