Gamma knife radiosurgery for NF2 associated vestibular schwannomas - The role of higher dose and cochlear implantation to rehabilitate hearing.Michael Link1, Bruce Pollock2, Colin Driscoll3, Robert Foote41Rochester, United States 2Dept. of Neurologic Surgery, Mayo Clinic 3Dept. of Otorhinolaryngology, Mayo Clinic 4Dept. of Radiation Oncology, Mayo Clinic Keywords: gamma knife, hearing preservation, vestibular schwannoma, cochlea, dose escalation
The purpose of this review was to evaluate the long-term outcome of NF2 associated vestibular scwannomas (VS) treated with Gamma Knife stereotactic radiosurgery (GKRS).
Specifically, we wanted to examine the rate of tumor control, and hearing preservation, and examine the role of cochlear implantation to rehabilitate hearing in patients after GKRS.
Between 1990 and 2010 32 VS in 26 patients were treated with GKRS. There were 10 women. The median age of the 26 patients was 37 years (range: 13 – 68 years).
The median clinical and imaging follow-up was 85 months (range 3 – 253 months). The median marginal dose was 14 Gy (range 12 – 20 Gy) and the median maximum prescribed dose was 28 Gy (24 – 40 Gy). The median tumor diameter in the posterior fossa was 15 mm (range 6 – 28 mm) and the median treatment volume was 2.65 c.c. (range 0.4 – 11.2 c.c.). The median marginal dose was 14 Gy (range 12 – 20 Gy) and the median maximum prescribed dose was 28 Gy (24 – 40 Gy). The median tumor diameter in the posterior fossa was 15 mm (range 6 – 28 mm) and the median treatment volume was 2.65 c.c. (range 0.4 – 11.2 c.c.). Four patients have undergone cochlear implantation (CI) following GKRS.
After a median follow-up of ~7 years 18 tumors (56%) were smaller with a median tumor reduction of 5 mm. Eight tumors (25%) remained unchanged in size and 6 tumors (19%) were clearly larger compared to the date of radiosurgery and had shown growth on more than one follow-up MRI scan. The median marginal dose for the tumors that decreased in volume was 15.5 Gy and the median marginal dose for the tumors that showed progressive enlargement was 13 Gy. Prior to GKRS 13 treated ears had AAO-HNS Class A or B hearing. In 6 patients an “only hearing ear” was treated. At last follow-up only 3/13 (23%) kept Class A or B hearing (PTA < 50 dB; WRS > 50%). Two of the four patients who received CI following GKRS have had excellent hearing rehabilitation. Reasons for this will be discussed.
This was a retrospective review.
GKRS for NF2 associated VS provides an opportunity for tumor control at higher doses than usually recommended for sporadic VS but is a poor hearing preservation strategy.
However, CI following GKRS, when performed soon after treatment and before a long duration of deafness may result in good hearing rehabilitation. Project Roles:
M. Link (), B. Pollock (), C. Driscoll (), R. Foote ()