In contrast to their benign counterparts, neurofibromas or schwannomas, intracranial MPNSTs carry a poor prognosis with a median OS of 9 months, (range 1 to 66 months, present review). In combined series of intracranial and extracranial MPNSTs, Zou et al report a 5-year survival rate of 38.7%, whereas Anghileri et al described a 5-year cause-specific mortality of 39.9%. When the influence of tumor site is considered, Anghileri reported an increased 5-year mortality of head and neck MPNSTs of 66.7%, as compared to 48.8% and 27.5% of trunk and extremities MPNSTs, respectively. The rarity of intracranial MPNSTs hampers the establishment of evidence based strategies for their optimal treatment. Thus, the management of the intracranial MPNSTs should also consider the experience gained from the treatment of extracranial MPNSTs.
Anghileri et al conducted a study of 205 patients with MPNSTs, of which 9 cases were head and neck tumors, and found that GTR, achieved in 62% of the patients, correlated significantly with longer OS, and inversely with local recurrence on multivariate analysis . Zou et al carried out another study of 140 patients with MPNSTs, including 20 tumours of the head and neck, and showed that a complete surgical resection was inversely related to local recurrence on univariate analysis . The results of the present review verify for intracranial MPNSTs the statistically significant influence of GTR upon OS in the univariate and multivariate analysis. Thus, a main goal in the treatment of the intracranial MPNSTs should be the complete surgical tumour resection with preservation of neurological function, whenever applicable.
The role of adjuvant radiotherapy remains controversial. Some studies suggest that radiation may be implicated in the pathogenesis of MPNSTs [8, 28].Foley et al suggested that ionizing radiation may cause chromosomal injury and induce proliferation as well as cytologic atypia in Schwann cells, resulting in radiation-induced MPNSTs .In our review series, 41.7% of patients harbouring a malignant transformation to MPNST received radiation in their history. Other studies haven't shown any positive effects of radiotherapy on patients outcome[30–32], while the recent literature indicates the beneficial role of the radiotherapy in local control of disease after a total or a near total resection of extracranial MPNSTs [14, 33–38]. Anghileri et al found adjuvant radiotherapy to be significantly related to longer OS on multivariate analysis, while no correlations with local recurrence or distant metastases were observed . The radiation dosage administrated in the majority of the cases was 50 - 60 Gy. Our review revealed the beneficial prognostic significance of adjuvant radiotherapy for OS in the univariate analysis. However, the multivariate analysis failed to show an independent influence of RT on OS. This could be related to the limited sample of patients. Considering the above findings and the highly malignant histological appearance of the tumour, in our patient we decided for adjuvant radiotherapy with stereotactic guidance due to its precise dosage delivery while sparing the adjacent healthy brain tissue. This strategy provides the possibility to apply an adequate high dose of 60 Gy despite of nearby sensitive risk structures like the brainstem. Thus, we were able to take advantages of both stereotactic radiotherapy and conventional fractionation while minimising the risks of RT-inducing brain injury like radiation necrosis and cognitive decline.
The optimal radiation dose has not yet been defined. We decided for a total dose of 60 Gy balancing the relatively high radiation dose to the highly malignant histological tumour appearance.
Some authors consider MPNSTs to be chemotherapy-resistant  while others suggest that surgery followed by combined radiochemotherapy results in improved survival . Two recent studies of large series of peripheral MPNSTs failed to show any benefit of chemotherapy [7, 34]. Therefore, in our patient, chemotherapy was decided to be spared for the case of tumour relapse or metastatic disease.
In the present patient the MPNST seems to have resulted from the malignant transformation of a pre-existing benign schwannoma. 36.1% of the review cases experience a progression of benign tumor to malignancy, having a worse OS compared to MPNSTs arising de novo. The latter difference though did not reach statistic significance (8.46 vs 22.95 months, p = 0.140). These observations point out the importance of a thorough long-time follow-up of all benign intracranial schwannomas and neurofibromas that have not been resected. However, it is not clear whether MRI follow-up can reliably indicate the exceptional transition of a schwannoma to a MPNST. Approximately, 25 to 50% of MPNSTs are associated with NF-1. The overall lifetime risk of genesis of MPNST in patients with NF-1 is estimated to be from 8 to 13% [14, 40]. In the present review 17.1% of intracranial MPNSTs were related to NF-1.
It is noteworthy, that the female gender is less likely to present with intracranial MPNST and that females harbouring this tumour have a significant longer OS than men. Further studies are needed to enlighten the background of these observations.