Malignant peripheral nerve sheath tumors (MPNST) represent a group of malignant spindle cell sarcomas with evidence of nerve sheath differentiation and/or arising from a peripheral nerve. Tumors showing origin from epineurial connective tissue or vascular structures are not considered to represent MPNST. Older/prior terminology for MPNST includes malignant neurilemmoma, malignant schwannoma, neurofi brosarcoma, and neurogenic sarcoma [ 1 ]. A number of histologic subtypes have been described. The majority are high grade aggressive sarcomas that show a strong tendency for local recurrence and metastases despite aggressive therapeutic measures [ 2 ].
Clinical Features and EpidemiologyThere is a strong association between MPNST and Neurofi bromatosis Type 1 (NF1), with 50 % of all MPNSTs arising within this patient population [ 3 ]. Approximately 10 % of individuals with NF1 will develop an MPNST over their lifetime, most of these tumors representing malignant degeneration occurring within preexisting plexiform neurofi bromas. One study of 476 NF1 patients documented a strong association between the presence of subcutaneous neurofi bromas and internal plexiform neurofi bromas, with an even stronger correlation between the presence of internal plexiform neurofi bromas and MPNST [ 4 ]. The remainder of MPNSTs will arise de novo, approximately 5-10 % representing radiation-induced sarcomas [ 1 ]. There is no particular gender predilection, and MPNSTs have been documented throughout a wide age range including children and the elderly. The majority however tend to present in adults with a median age in the mid 40s [ 5 ]. MPNSTs arising in the NF1 population tend to present up to a decade earlier, and these patients' tumors also tend to be larger [ 3 , 6 ].The majority of MPNST arise from larger peripheral nerves or within deep soft tissues, the most frequent sites including brachial plexus, sciatic, and paraspinal nerves, proximal upper and lower extremities, and buttock regions [ 5 ]. They have also been documented in a wide variety of locations throughout the body. Well over 50 cases of spinal MPNST have been reported [ 7 -13 ]. No particular spinal level is preferentially involved, and interestingly a significant proportion of spinal MPNST exhibit rhabdomyoblastic elements (Malignant Triton Tumor; see histologic description below) [ 14 -17 ]. MPNST represents one of the most aggressive tumors that may involve structures of the head and neck region [ 6 ]. It may arise from cranial nerves, particularly the vestibular [ 18 ], vagus [ 18 ], facial [ 18 , 19 ], and trigeminal [ 19 , 20 ]. Other sites include not only brachial plexus [ 21 ], but also scalp and bony structures (base of skull [ 22 -25 ], sinuses [ 26 , 27 ], and bones of the jaw) [ 28 , 29 ]