malignant peripheral nerve sheath tumor ( mpnst ) is a rare soft tissue sarcoma of the ectomesenchymal origin . it is the malignant counterpart of benign soft tissue tumors like neurofibromas and schwannomas and may follow them . common sites include deeper soft tissues , usually in the proximity of a nerve trunk . mpnsts can develop in any anatomical region , but the sciatic nerve is affected most often . the incidence of mpnst in the general population is 0.001% ; however , it can increase to 5 - 42% in patients with neurofibromatosis type 1 ( nf 1 ) . mpnst arising de - novo at an unusual site without any features of nf 1 as has been noticed in our cases is interesting to report . a 35-year - old woman presented with 2-month history of rapidly progressive painless swelling in left orbitotemporal region with proptosis and blurring of vision leading to complete blindness . physical examination revealed a lobular nontender , firm mass of size 15  7 cm extending from left orbit to the left temporal region . in addition to axial proptosis , the left eye showed restricted movement in all directions [ figure 1a and b ] . magnetic resonance imaging ( mri ) of the orbits and brain showed left sphenoidal - based extra - axial marginated in homoginously enhancing mass at the lateral side of the left optic nerve buckling the ipsilateral anterotemporal lobe [ figure 2 ] . the histopathology and immunohistochemistry of the lesion revealed mpnst [ figure 3a and b ] . vision in her left eye improved to finger counting at 1 m and extraocular movements were normal . on 6-month follow - up , the patient is doing well with no local recurrence or any distant metastasis . ( a ) preoperative photograph . ( c ) postoperative cosmesis and ( d ) excised tumor mass magnetic resonance imaging of the orbit and brain showing left sphenoidal - based extra - axial plane ( a ) and contrast ( b ) marginated in - homoginously enhancing mass at the lateral side of the left optic nerve buckling the ipsilateral antero temporal lobe ( a ) histopathology picture showing fascicles of spindle cells with marked hypercellularity and high mitotic activity suggestive of mpns . ( b ) immunohistochemistry demonstrates s-100 protein staining of the tumor tissue a 60-year - old male presented with rapidly enlarging painless swelling in back with lower limb weakness in a period of 2 month . on examination , lower motor type of paralysis was found in both the legs with power : 0/5 around all joints . a nontender hard lobulated mass of size 10  5 cm was found over left lumbar paraspinal area fixed to underlying structure [ figure 4a ] . mri was suggestive of lumbar ( l1-l4 ) extradural lesion with associated l3 vertebral body compressional collapse giving a picture of neurofibroma [ figure 5 ] . patient improved neurologicaly with power 2/5 around all joints in lower limb . on completion of local radiotherapy at 6-month follow - up , the patient was doing well with no local or systemic spread . clinical photograph ( a ) of case-2 showing the left lumbar mass ( yellow arrow ) with excised tumor tissue ( b ) magnetic resonance imaging of spine in sagittal view shows a t1 ( b ) hypo , t2 hyper ( a ) heterogenously enhancing lumbar ( l1- l4 ) extradural mass lesion with associated l3 vertebral body compression collapse a 35-year - old woman presented with 2-month history of rapidly progressive painless swelling in left orbitotemporal region with proptosis and blurring of vision leading to complete blindness . physical examination revealed a lobular nontender , firm mass of size 15  7 cm extending from left orbit to the left temporal region . in addition to axial proptosis , the left eye showed restricted movement in all directions [ figure 1a and b ] . magnetic resonance imaging ( mri ) of the orbits and brain showed left sphenoidal - based extra - axial marginated in homoginously enhancing mass at the lateral side of the left optic nerve buckling the ipsilateral anterotemporal lobe [ figure 2 ] . the histopathology and immunohistochemistry of the lesion revealed mpnst [ figure 3a and b ] . vision in her left eye improved to finger counting at 1 m and extraocular movements were normal . on 6-month follow - up , the patient is doing well with no local recurrence or any distant metastasis . ( a ) preoperative photograph . ( c ) postoperative cosmesis and ( d ) excised tumor mass magnetic resonance imaging of the orbit and brain showing left sphenoidal - based extra - axial plane ( a ) and contrast ( b ) marginated in - homoginously enhancing mass at the lateral side of the left optic nerve buckling the ipsilateral antero temporal lobe ( a ) histopathology picture showing fascicles of spindle cells with marked hypercellularity and high mitotic activity suggestive of mpns . a 60-year - old male presented with rapidly enlarging painless swelling in back with lower limb weakness in a period of 2 month . on examination , lower motor type of paralysis was found in both the legs with power : 0/5 around all joints . a nontender hard lobulated mass of size 10  5 cm was found over left lumbar paraspinal area fixed to underlying structure [ figure 4a ] . mri was suggestive of lumbar ( l1-l4 ) extradural lesion with associated l3 vertebral body compressional collapse giving a picture of neurofibroma [ figure 5 ] . patient improved neurologicaly with power 2/5 around all joints in lower limb . on completion of local radiotherapy at 6-month follow - up , the patient was doing well with no local or systemic spread . clinical photograph ( a ) of case-2 showing the left lumbar mass ( yellow arrow ) with excised tumor tissue ( b ) magnetic resonance imaging of spine in sagittal view shows a t1 ( b ) hypo , t2 hyper ( a ) heterogenously enhancing lumbar ( l1- l4 ) extradural mass lesion with associated l3 vertebral body compression collapse malignant peripheral nerve sheath tumor ( mpnst ) is the preferred term for tumors originating from peripheral nerves or their sheaths and it has replaced the previous entities such as malignant schwannoma , malignant neurilemmoma and neurofibrosarcoma . they may arise spontaneously , although in 5 - 42% of cases an association with neurofibromatosis ( nf ) type 1 is known . the common sites of origin include the extremities and trunk , usually sciatic nerve , brachial plexus and the sacral plexus . to our knowledge , few patients with a cranial or facial mpnst have been reported . likewise , cranial nerves are rarely affected , although tumors of the trigeminal and acoustic nerves have been reported . although rare , reports of mpnst arising at unusual sites have been documented by various authors [ table 1 ] . firat et al . , had reported an interesting case of arm mpnst with metastatic involvement of ipsilateral axillary lymph node , brachial plexus and pleura in a geriatric patient having multiple neurofibromas of different sizes almost covering his entire body , massively . published clinical studies and case reports of mpnsts at unusual sites most cases are large , fleshy , often necrotic neoplasms averaging more than 5 cm in diameter . mpnsts are fusiform to globular in shape and vary from white and firm to yellow and soft , depending on the absence or presence of necrosis . although the tumors usually appear well circumscribed , they are not truly encapsulated . the tumor in our case was greyish white , firm , with foci of hemorrhage and necrosis [ figures 1d and 4b ] . the histological features of mpnsts are those of a highly cellular , spindle - cell neoplasm resembling a soft - tissue sarcoma , but with differentiation toward elements of the nerve sheath , schwann cell , and perineural cell . such atypical components show hypercellularity , an increased nuclear - to - cytoplasmic ratio , cytological atypia and increased mitotic activity . the histological spectrum of mpnst is broad and the diagnosis rests on combination of some microscopic features , none of which is diagnostic by itself . s100 protein , the most widely used antibody for nerve sheath tumor , is positive only in 50% of mpnsts . another diagnostic , leu 7 immunoreactivity , is reported to be positive in 30 - 40% of the cases . our case showed immunopositivity with s100 protein and was negative for other schwann cell markers . data suggest that leu-7 is an important marker of schwann cell neoplasms , although it is not superior to s100 protein . moreover , combined immunohistochemical evaluation of potential schwann cell markers including leu-7 , mbp , gfap and ln3 using commercially available antibodies offers no advantage over analysis of s100-protein immunoreactivity alone . the most important features adversely influencing prognosis are the presence of von recklinghausen 's disease , a tumor larger than 5 cm and extent of resection . the differential diagnosis between benign schwannoma and neurosarcoma may be challenging : one must look for necrotic foci , the number of atypical mitoses , and an absence of differentiated cells . tumors larger than 5 cm , histological grades ii and iii , an association with neurofibromatosis , and regional or distant metastases suggest an ominous prognosis . the treatment of choice is surgery , but postoperative radio- and chemotherapy are part of adjunctive therapy . when radical tumor removal is not possible , excision combined with high - dose radiation therapy seems to be the best alternative treatment . with the latest advances in molecular genetics , the target therapy for this tumor type is expected to be discovered . suspicion of mpnst should be raised in rapidly growing painless tumor in and around a nerve tissue .
malignant peripheral nerve sheath tumor ( mpnst ) is a rare soft tissue sarcoma . 
 most arise in association with major nerve trunks . 
 their most common anatomical sites are the proximal portions of the upper and lower extremities and the trunk . 
 mpnsts have rarely been reported in literature to occur in other unusual body parts . 
 we review all such cases reported till now in terms of site of origin , surgical treatment , adjuvant therapy and outcome and shortly describe our experience with two of these cases . both of our case presented with lump at unusual sites resembling neurofibroma , one at orbitotemporal area and other in the paraspinal region with characteristic feature of neurofibroma with the exception that both had very short history of progression . 
 they underwent gross total removal of the tumor with adjuvant radiotherapy postoperatively . at 6-month follow - up 
 both are doing well with no evidence of recurrence .