On “Malignant Transformation of Acoustic Neuroma/Vestibular Schwannoma 10 Years after Gamma Knife Stereotactic Radiosurgery” (Skull Base 2010;20:381–388)

It was with great interest that we read the article titled “Malignant Transformation of Acoustic Neuroma/Vestibular Schwannoma 10 Years after Gamma Knife Stereotactic Radiosurgery” by Demetriades et al in the September 2010 issue of Skull Base.[1]

We were surprised to see that the authors identified only 13 cases. We did a literature review and found 36 cases of malignant acoustic tumors. In two cases, the tumors have grown rapidly 7 years and 2 years consecutively and the patients passed away shortly without confirmation of the malignancy. There were nine reports that described malignancy in neurofibromatosis type 2 (NF2) patients, and interestingly, all of these nine patients had received stereotactic radiation as initial treatment for their tumor (Table [1]).[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30]

Table 1 Summary of Reported Cases of Malignant Vestibular Schwannoma Authors Age/Sex Side NF2 Pathology Previous Irradiation Survival Dastur 19672 38/M L N Melanotic schwannoma N 8 mo Kudo 19833 54/M R N MPNST N 1 mo Miller 19864 74/M N/A N/A Melanotic schwannoma N N/A Hernanz-Schulman 19865 2/F N/A N MPNST N N/A Best 19876 24/F R N Triton N 1.5 mo McLean 19907 75/M R N MPNST N 2 mo Han 19928 47/F R N Triton N 2 wk Maeda 19939 38/M R N Triton N 3 mo Mrak 199410 40/M L N MPNST N 36 mo Earls 199411 77/M L N Melanotic schwannoma N N/A Norén 199812 18/F R Y Triton Y N/A Comey 199813 50/M R N Triton Y 24 mo Thomsen 200014 19/F R Y Sarcoma Y 12 mo Saito 200015 69/M L N MPNST N N/A Baser 200016 N/A N/A Y MPNST Y N/A Baser 200016 N/A N/A Y MPNST Y N/A Baser 200016 N/A N/A Y MPNST Y N/A Hanabusa 200117 51/F R N Sarcoma Y Autopsy Bari 200218 28/F L Y MPNST Y 3 mo Shin 200219 26/F R N MPNST Y 10 mo Ho 200220 14/F L Y Rapid growth Y 2 wk McEvoy 200321 22/M R Y Rapid growth Y 3 mo Wilkinson 200422 53/M R N MPNST Y N/A Kubo 200523 51/M L N MPNST Y N/A Muracciole 200424 61/F L N Triton Y N/A Maire 200625 N/A N/A N MPNST Y N/A Gonzalez 200726 43/F L N MPNST N 8 mo Chen 200827 62/F L N MPNST N 4 mo Scheithauer 200928 67/M R N MPNST N 1 mo Scheithauer 200928 56/M R N MPNST N 2 mo Scheithauer 200928 50/M L N MPNST N 36 mo Scheithauer 200928 32/M L N MPNST N 3 mo Scheithauer 200928 5/M L N MPNST N N/A Van Rompaey 200929 53/F R N MPNST Y Autopsy Yang 201030 74/M L N Sarcoma Y 2 mo Demetriades 20101 37/M L N MPNST Y 6 mo L, left; MPNST, malignant peripheral nerve sheath tumor; N, no; N/A, not available; NF 2, neurofibromatosis type 2; R, right; Y, yes.

It should also be noted that two of the cases identified by the authors referred to the same patient. In fact, Kudo and Matsumoto and colleagues have published the same case of malignant vestibular schwannoma twice: the first time in English and the second time in Japanese, 7 years later.[3] [31]

In addition, the experience from the National Centre for Stereotactic Radiotherapy in Sheffield showed not only one astrocytoma after gamma knife surgery for a cavernoma but also a new appearance of a glioblastoma multiforum in a patient 3 years after receiving radiotherapy for the treatment of his vestibular shwannoma.[32]

We agree with the authors that long-term follow-up is mandatory after gamma knife treatment, because most of the malignant transformation appeared at least 5 years after the initial radiotherapy, and in one case, it appeared after 19 years.[25]

Therefore, even if stereotactic radiotherapy is widely used for vestibular schwannoma treatment in patients with small tumor and good hearing, we think that this therapeutic modality should be avoided or at least used with caution in NF2 cases and young patients.

REFERENCES

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