her medical history included a spine operation due to tuberculous spondylitis of the lumbar spine about 10 years ago . the initial brain computed tomography ( ct ) scan ( brilliance 64-multislice ct scanner , philips medical system , ma ) demonstrated a well - defined intra - axial mass in the cerebellum ( fig . the mass was mainly located in the right cerebellar hemisphere , displacing the cerebellar vermis to the left side and compressing the right side of the 4th ventricle and resulting in mild obstructive hydrocephalus . the mass was composed of a peripheral isoattenuation area and a central low attenuation area , which was the central necrotic portion in the precontrast ct scan ( fig . the isoattenuation area of the mass demonstrated heterogeneous dense enhancement after the injection of contrast materials . some vascular or linear enhancing portions were observed , but the central low attenuation portion was scarcely enhanced . one day after admission , brain magnetic resonance imaging ( mri ) ( twin speed 1.5 t mr scanner , ge healthcare , wi ) was performed . the mass was hypointense on precontrast t1-weighted images ( repetition time [ tr]/echo time [ te ] , 400/-8 ms ) ( fig . ( tr / te , 3700/-1200 ms ) , the mass showed an intermediate signal intensity at the periphery , and central hyperintensity ( fig . the outer surface margin was comparatively smooth and slightly lobulated , but the inner surface margin was very irregular . after contrast material injection , the periphery showed heterogeneous enhancement as did the brain ct images ( fig . gradient echo images ( tr / te , 500/-15 ms ) revealed multiple bleeding foci in the periphery as dark signal intensity foci ( fig . f - fluorodeoxyglucose positron emission tomography / computed tomography ( f - fdg pet / ct ) demonstrated hypermetabolism at the tumor periphery . there was a metabolic defect within the central area of the tumor , which was correlated to the central necrosis of the tumor ( fig . macroscopically , it was a relatively well - circumscribed and firm mass with areas of necrosis and hemorrhage . microscopically , it had a biphasic pattern with areas of gliomatous and sarcomatous differentiation ( fig . the gliomatous component consisted of atypical glial cells with pleomorphic nuclei and frequent mitotic figures . geographic necrosis and endothelial cell proliferation the tumor predominantly consisted of spindle cell proliferation forming sarcomatous areas with intersecting fascicular or storiform patterns similar to fibrosarcoma . extensive necrosis , frequent mitotic figures ( > 80/10 hpfs ) and abnormal mitoses were observed in the sarcomatous component ( fig . the gliomatous component showed immunoreactivity for glial fibrillary acid protein ( gfap ) , in contrast with lack of immunoreactivity for gfap in the sarcomatous component ( fig . abundant collagen and reticulin fibers were found between individual tumor cells in the sarcomatous component using masson - trichrome and reticulin staining ( fig . almost all previously reported cases of gliosarcoma were located in the supratentorial area , especially in the peripheral region of the temporal lobe ( 2 ) . gliosarcoma occurs less commonly in the frontal , parietal or occipital lobes , and in the corpus callosum . ( 3 ) showed similar mri findings to supratentorial gliosarcoma such as peripheral location of the cerebellum , broad base on the meninges , and multiple lesions . other brain and spinal gliosarcoma cases usually had a medical history of radiation therapy for other cerebellar tumors . quite a number of gliosarcomas have been reported as secondary tumors after radiation therapy for histologically different primary cns tumors ( 5 - 9 ) . among several possible mechanisms for gliosarcoma histogenesis , the transformation theory , which states that part of a glial tumor is dedifferentiated to primitive cells and transformed into sarcomatous components , supports the idea that radiation therapy might induce a dedifferentiation of the glial cell to the sarcomatous cells in cases with previous cns tumors ( 4 , 6 , 8 , 10 , 11 ) . compared to the previous literature , our case had no history of previous radiation therapy for a cns tumor . in addition , its location was in a relatively central portion , without abutting the meninges . pathologically , gliosarcoma is characterized by a biphasic tissue pattern with alternating areas of glial and mesenchymal differentiation ( 7 ) . the sarcomatous component shows malignant changes of spindle cells with features of fibrosarcoma or malignant fibrous histiocytoma . areas of mesenchymal differentiation into cartilage , bone , fat and smooth or skeletal muscle may be associated . in our case , although no specific mesenchymal differentiation was seen , the tumor was predominantly sarcomatous and had a mixture of clearly malignant mesenchymal gfap - negative areas and gfap - positive glial areas . therefore , we were able to exclude the possibility of glioblastoma with a florid fibroblastic proliferation . radiologic findings of gliosarcomas in the previous literature are variable and sometimes the tumors are very aggressive . a gliosarcoma may appear as a well - defined hyperdense mass with heterogeneous or ring enhancement due to a fibrous component . in contrast , a glioblastoma usually shows low or intermediate attenuation in a precontrast ct scan . vasogenic edema often accompanies glioblastoma , but central necrosis is less common due to the predilection of such tumors to develop in a peripheral location . dural involvement is not uncommon due to its peripheral location ( 3 , 5 , 12 ) . on mri , gliosarcoma appears as a heterogeneous mass both in t1- and t2-weighted images , with strong peripheral enhancement and central hemorrhage or necrosis ( 5 ) . extracranial metastasis is also common in gliosarcomas , resulting in a worse prognosis ( 8 , 10 ) . in our case , the imaging findings were similar to those of an infratentorial glioblastoma , which usually presents as an aggressive heterogeneous tumor with hemorrhage , necrosis , a cystic portion or calcification , and surrounding peritumoral edema ( 15 ) . but , it is known as a less aggressive and slower growing tumor than a supratentorial glioblastoma , and sometimes there is a lack of peritumoral edema , as in our case ( 16 , 17 ) . in addition , as the most common incidence of both tumors occurs between the 5th and 7th decades of life , it was very difficult to make the differential diagnosis . common differential diagnoses for gliosarcoma are glioblastoma , metastasis , brain abscess or other infratentorial intraaxial tumors such as hemangioblastoma or medulloblastoma ( 5 , 12 , 15 - 17 ) . in conclusion imaging findings were so similar to those of an infratentorial or supratentorial glioblastoma that it was difficult to distinguish from a glioblastoma . though a rare entity , gliosarcoma should be considered in the differential diagnosis of infratentorial tumors with radiological features of glioblastoma and metastasis in elderly patients .
gliosarcoma is a rare central nervous system tumor usually located in the supratentorial area . here 
 we report a rare case of a gliosarcoma that developed in the cerebellar hemisphere in a 70-year - old woman . 
 computed tomography ( ct ) and magnetic resonance imaging ( mri ) of the brain revealed an infratentorial mass of which radiological features were similar to those of glioblastoma . 
 the tumor was diagnosed by pathology as a gliosarcoma . though rare 
 , gliosarcoma should be considered in the differential diagnosis of infratentorial tumors with radiological features of glioblastoma or metastasis in elderly patients .