Malignant peripheral nerve sheath tumor
Malignant peripheral nerve sheath tumors (MPNST) are infiltrating, aggressive tumors belonging to the group of soft tissue sarcomas.
They may arise from any cranial or somatic nerve.
Classification
The World Health Organization Classification of Tumors of the Central Nervous System 2016 designates two subtypes of malignant peripheral nerve sheath tumor (MPNST): epithelioid MPNST and MPNST with perineurial differentiation. These were considered sufficiently distinct clinically to warrant designation as variants, whereas other subtypes such as MPNST with divergent differentiation (malignant Triton tumor, glandular MPNST, etc.) simply represent histologic patterns.
Epidemiology
The incidence of malignant peripheral nerve sheath tumor (MPNST) is approximately 0.001%. Those involving intracranial nerves are even more exceptional.
The published literature suggests that malignant peripheral nerve sheath tumors (MPNST) occur at increased frequency in neurofibromatosis type 2 (NF2). A review based on incidence data in North America showed that 1 per 1000 cerebellopontine angle nerve sheath tumors were malignant.
Treatment
The optimal treatment is resection, and the role of adjuvant treatment is unclear.
The explosion of molecular and preclinical data in recent years gives hope that we may be starting to gain some traction over this complexity. In particular, targeting of both the TOR and hsp90 pathways appears to be one strategy of considerable promise based on existing data; results of early clinical trials employing this approach are eagerly awaited, as are those of other combinations involving TOR inhibitors. The complexity of ras signaling is an obvious target but has proved a nettlesome signaling pathway to target to date, although downstream elements such as MEK may be more easily inhibited. Focus on novel proapoptotic agents such as survivin inhibitors is another broad approach to cancer that may be beneficial in this aneuploid group of cancers. Continued efforts should be undertaken to better understand tumor resistance to systemic therapy, crosstalk and alternative activation pathways, so that effective early clinical studies can be designed employing rational combinations of targeted agents.
In this rare and diagnostically challenging disease, efforts already underway must aspire toward innovative trial designs that maximize patient resources, buttressed by multicenter collaborations to improve the quality and quantity of meaningful translational and clinical data. With these efforts, the significant challenges to improve care for patients with this form of soft tissue sarcoma can be met 1).
Outcome
MPNSTs behave aggressively, with a high rate of local recurrence and a propensity to metastasize.
The median survival with best therapy is 49 months.
Case series
Three patients with a tumorous swelling in the entire inferior alveolar nerve (IAN) with similar disease courses suspect for a MPNST, which is particularly rare in the trigeminal nerve.
Diagnostic tools, surgical proceedings and reconstructive procedures were highlighted. Three male patients (58-68 years), who suffered from numbness, pain and mild swelling in the sensation area served by the mental nerve presented at the department of oral and maxillofacial surgery and underwent diagnostic workup including CT, MRI, F18-PET-CT, as well as a biopsy of the clinical visible tumor mass with histopathological and molecular pathological analysis.
MR imaging revealed the full extent of the tumor comprising the course of the entire mandibular nerve (one case bilateral) starting in the trigeminal ganglion through the IAN and ending in the mental foramen. Hence, both a neurosurgical and maxillofacial intervention with jaw replacement were necessary. Adjuvant radiation of the intracranial closed resection margins, and in one case of parts of the mandible was required.
In order to reveal the full extent of tumor spread of MPNSTs sufficient preoperative imaging is crucial as it is an important step in therapy planning. MRI and PET-CT are the imaging modalities with the best prospect of success in depicting the whole extent of the disease. Radical surgical management is the treatment of choice whereas radiochemotherapy shows an ancillary part 2).
2010
Ziadi et al. identified 32 cases of cranial MPNST including one case. The age ranged from 5 to 75 years old with most patients being in the 5th and 6th decade. Male to female ratio is 2.5:1. Most cases are developed sporadically (50%), 31% arise from a malignant transformation of schwannoma and 19% from a neurofibroma. Imaging findings were not specific. The cranial nerve VIII is the most involved (15/32), followed by the Vth (10/32) and the VIIth (5/32). 4 cases had neurofibromatosis type 1 and 2 had neurofibromatosis type 2. MPNST will strongly express protein S-100 and collagen IV-laminin. 13 cases were treated with radiotherapy for tumor recurrence and metastases. In these cases the survival rate was better than the cases without radiotherapy. Fatal outcome occurred in 66% of patients whereas 19% were reported alive with or without complications. The seven cases reported to have metastases were entirely to the spine. The mean time of recurrence or metastases is 12.2 months.
MPNST of cranial nerves are very rare. In neurofibroma, even though MPNST is mainly associated to type 1, we should keep in mind its association to NF2. Mainstay of treatment is radical resection with adjuvant radiotherapy. Inaccessibility of cranial MPNST may explain the subtotal resection and thus the poor prognosis. metastases to the spinal cord is the most frequent one. A close postoperative follow-up is mandatory to eliminate recurrence 3).