teratomas are congenital tumors that are usually found in the gonads , and are only rarely detected in extragonadal areas , such as , the mediastinal , retroperitoneal and sacrococcygeal regions . to the best our knowledge , an extragonadal teratoma of the long bone has not been previously reported in the literature . we describe clinical , radiologic and pathologic findings of an exceedingly rare case of malignant teratoma of the proximal humerus . a 14-yr - old female was admitted with painful limited motion of the left shoulder joint . she was transferred to our institute for further study and proper management under impression of malignant bone tumor . on physical examination , however , a radiograph of the humerus showed ill defined moth eaten to permeative destructive lesion associated with cortical perforation of proximal humerus ( fig . 1a ) . magnetic resonance imaging ( mri ) well demonstrated the entire extent of the tumor , which showed inhomogeneous enhancement after contrast agent administration . both the intraossoeus and extraosseous tumor components were evident on transaxial gradient - echo mr images ( fig . 99 m tc - mdp scintigraphy and an f - fdg whole body positron emission tomography ( pet ) scan showed uneven increased uptake at the left proximal humerus , but no other abnormality was detected . initial diagnostic considerations included ; leukemic infiltration , lymphoma , osteomylelitis , and a malignant bone tumor , such as , an osteosarcoma . a subsequent surgical biopsy was performed and the pathological report revealed an immature bony teratoma . on gross inspection , the cut surface of the resected proximal humerus showed a homogenous grayish white flesh - like tissue that had replaced the whole epimetaphysis and a part of the diaphysis ( fig . malignant teratoma were graded using a method described by robboy and scully ( 1 ) ; degree of immaturity , presence and quantity of a neuroepithelial component . grade 1 tumors with rare foci of immature neuroepithelial tissue occupy less than one low power field ( 40x ) , grade 2 tumors occupy 1 to 3 , and grade 3 tumors occupy more than 3 low power fields . the latter looked immature in appearance , which is not found in normal adult tissue . immunohistochemical staining demonstrated the expressions of glial fibrillarary acidic protein ( gfap ) and cd56 expression in neuronal tissue ( fig . based on the above - mentioned grading system , the tumor of the present case was classified as a grade 1 immature teratoma bearing immature endodermal glandular structures . there was no evidence of local recurrence or distant metastasis at 30 months postoperatively . according to the musculoskeletal tumor society scoring system ( 2 ) , teratomas are germ cell neoplasms that include tissues arising from the three germ cell layers ( 3 ) . they usually originate from pluripotent cells , which can differentiate to a wide variety of tissues . the majority of extragonadal teratomas develop from germinal elements , and they usually occur along the migration pathway of the germ cells ( 4 ) . resultantly , the sacrococcygeal region is the most frequent extragonadal location ; other sites include the mediastinum and retroperitoneum ( 5 ) . exceptionally rarely intraosseous teratoma has reported but there has been no reported case involving a long bone in the literature . in 1992 , chinoy et al . ( 6 ) reported a case of an extragonadal malignant teratoma of the foot and in 2000 , vazquez et al . ( 7 ) described an intraosseous teratoma of the iliac bone . in these previously published reports , initial diagnostic considerations included fibrous dysplasia , langerhans ' cell histiocytosis , aneurysmal bone cyst and a malignant bone tumor , such as , an osteosarcoma . most skeletal germ cell tumors are metastatic ( 8) but the pathogenesis of teratoma in the appendicular skeleton is still enigmatic . another possible pathogenetic theory concerns the heterotopic location of extragonadal germ cells . however , the humerus is not in the migration path of germ cells , and in fact , no teratoma has been identified previously at this site . thus , we are uncertain about the pathogenesis of the bony teratoma in this case . nevertheless , since the tumor was confirmed as a grade 1 immature teratoma , a wide surgical excision only was undertaken for comprehensive treatment . she is doing well without evidence of local recurrence or distant metastasis at final follow - up examination .
a extragonadal malignant teratoma of the extremity is a rare pheonemenon . 
 we describe a extremely rare case of malignant teratoma of the left proximal humerus in a 14-yr - old female . 
 radiologic evaluations , including magnetic resonance imaging , suggested a malignant bone tumor , but a pathological examination revealed an immature bony teratoma . 
 bone scintigraphy and positron emission tomography computed tomography scan showed increased uptake of proximal humerus but no other abnormal lesion .