it is a relatively common tumor , comprising approximately 5% of all benign soft tissue tumors , and shows a predilection to affect the sensory nerves .
intraosseous neurilemmoma , however , is very rare , accounting for less than 1% of benign bone tumors .
the mandible is the most frequently affected site , followed by the sacrum ; this tumor rarely arises in the bones of the extremities .
only 2 cases of intraosseous neurilemmoma around the elbow have been described in literature ; these cases arose in the distal humerus .
a 21-year - old woman was referred to our orthopedic unit with a 1-month history of pain in the left elbow .
the initiating factor , such as trauma , was not clear . on physical examination , the overlying skin was intact , and there was no evidence of warmth , erythema , or induration .
no other masses were palpable . the elbows and forearms had a normal range of motion ( rom ) .
plain radiographs revealed a well - defined , lytic , and expansile lesion , with thin marginal sclerosis and trabeculation in the proximal ulna ( fig .
1 ) . computed tomography ( ct ) showed considerable destruction of the cortex of the ulna , which connected with a mass of soft tissue . at the edge of
2a ) , which had invaded into the cortex , and no periosteal reaction was seen ( fig .
2b ) . magnetic resonance imaging ( mri ) showed the well - defined and lobulated lesion to be isointense to skeletal muscle on t1-weighted images , and heterogeneous and hyperintense on t2-weighted images .
the lesion revealed uniform enhancement following gd - dtpa administration . because of uncertainty regarding the histological origin of the tumor , we performed an open biopsy . the pathologic specimen consisted of hypercellular regions with palisading nuclei ( antoni type a ) , and hypocellularity regions with myxoid background ( antoni type b ) .
curettage was performed on the bone lesion , and the resulting deficit was grafted with beta - tricalcium phosphate ( fig .
after 3.5 years of follow up , the patient is clinically asymptomatic , and the radiographs show complete graft incorporation ( fig .
the patient was informed that the case would be submitted for publication and her consent was obtained .
neurilemmomas may involve bone tissue via 3 mechanisms : ( 1 ) they may be intramedullary , producing rarefaction of the bone ; ( 2 ) they may be located within the nutrient canal , with the formation of a dumbbell - shaped tumor ; or ( 3 ) they may be extraosseous , eroding into the bone . with regard to the comparatively high incidence of intraosseous neurilemmoma in the mandible , it has been speculated that the long intraosseous path of the mandibular nerve may predispose to metaplasia of the schwann cells in its nerve sheath .
however , some authors have refuted this theory , noting that the nerves innervating the long bones through the nutrient foramina are longer than the mandibular nerve ; nevertheless , the frequency of intraosseous neurilemmoma in the long bones is several times lower than that in the mandible .
de la monte and colleagues have suggested that the death of sensory nerve fibers within bone tissue may account for the exceedingly rare occurrence of intraosseous neurilemmoma . we think that the high frequency of neurilemmoma in the mandible is not because of the long intraosseous course , but because the mandibular nerve consists of sensory nerves of the trigeminal nerve origin .
the characteristic radiographic features of intraosseous neurilemmoma include the following : ( 1 ) a well - defined lytic lesion , ( 2 ) sclerotic margins , ( 3 ) lobulated or trabeculated contours , ( 4 ) cortical expansion , and ( 5 ) absence of central calcification . however , the radiographic findings are non - specific .
it is difficult to differentiate intraosseous neurilemmoma from other benign neoplasms of such osseous lesions , including solitary bone cyst , aneurysmal bone cyst , giant cell tumor , non - ossifying fibroma , benign fibrous histiocytoma , desmoplastic fibroma , fibrous dysplasia , chondromyxoid fibroma , and enchondroma .
on ct , we can confirm the origin of the tumor when there is soft tissue extension of the tumor .
if the origin is intraosseous instead of periosteal , no periosteal reaction is seen , and the edge of the destructed cortex will be overhung by a soft tissue mass .
young and colleagues pointed out that the aspect of the overhanging edges of cortical bone can assist in distinguishing between an intraosseous desmoplastic fibroma versus a periosteal desmoplastic fibroma .
similarly , intraosseous neurilemmoma is considered to originate from intraosseous nerves rather than from periosteal nerves , if ct shows overhanging edges of cortical bone . in our case and in others
this may be the characteristic finding of intraosseous neurilemmoma provided the tumor expands within the nutrient canal of the cortex .
the final diagnosis of intraosseous neurilemmoma was not made until after histologic examination of tissue obtained during excision .
the diffuse immunoreactivity for s-100 protein is indicative of a schwann cell origin , and helps distinguish this tumor from other benign spindle cell lesions of similar histology .
the recommended treatment for intraosseous neurilemmoma is conservative resection and bone grafting , as malignant change is extremely rare .
recurrence also is rare following complete local excision . in previous reports , after performing only curettage , curettage and bone grafting , or en block resection , local recurrence only occurred in 2 cases .
these authors did not refer to the reason for local reference , but recurrence of the tumor is not evidence of malignant transformation . in our case
owing to the infrequency of an intraosseous neurilemmoma , the diagnosis is often not even suspected until histologic evaluation after a biopsy .
although very rare , intraosseous neurilemmoma should be taken under consideration in the differential diagnosis of painful , radiographically benign - appearing osseous tumor around the elbow .
written informed consent was obtained from the patient for publication of this case report and accompanying images .
a copy of the written consent is available for review by the editor - in - chief of this journal on request .
case report writing , data collection , and discussion writing were done by munehisa kito and yasuo yoshimura .
discussion writing was carried by kenichi isobe , kaoru aoki , takashige momose , and hiroyuki kato .
 introductionneurilemmoma is a benign nerve sheath neoplasm commonly located in the soft tissue . 
 intraosseous neurilemmoma is rare , constituting less than 1% of primary bone tumors.presentation of casea 21 year - old woman was presented with left elbow pain of 1-month duration . 
 plain radiographs showed a well - defined , lytic and expansile lesion of the proximal ulna . computed tomography revealed cortical destruction and soft tissue extension . because the tissue of origin for the tumor was uncertain , an open biopsy was performed . 
 the specimens demonstrated a benign spindle cell tumor suggestive of a neurilemmoma , similar to a soft tissue neurilemmoma . 
 the diagnosis of intraosseous neurilemmoma was established . 
 marginal excision of the soft tissue component and curettage of the lesion in the bone were performed . 
 after 3.5 years of follow up , there is no clinical or radiographic finding to suggest any recurrence.discussionthe major site of intraosseous neurilemmoma is the mandible . 
 occurrence in the long bone is particularly rare . 
 only two cases of intraosseous neurilemmoma involving the bones around the elbow have been reported to our knowledge ; these cases arose in the distal humerus . 
 we describe the first case of intraosseous neurilemmoma of the proximal ulna of the left elbow . 
 the recommended treatment is conservative resection and bone grafting , as malignant change is extremely rare.conclusionalthough very rare , intraosseous neurilemmoma should be taken under consideration in the differential diagnosis of painful , radiographically benign - appearing osseous tumor around the elbow . 
Introduction
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Discussion
Conclusion
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