Abstract：Objective: To investigate the conventional MRI, diffusion-weighted imaging(DWI) characteristics of supratentorial primitive neuroectodermal tumors(PNET) and correlate them with pathological findings. Methods: Fifteen patients with supratentorial PNET were confirmed pathologically, the conventional MRI, DWI features and pathological data of supratentorial PNET were analyzed. The apparent diffusion coefficient(ADC) values from the solid portion of tumor and the normal contralateral white matter were measured quantitatively, statistical analysis was performed with two sample t-test. Results: Most tumors were localized in cerebral subcortex, the mean maximum diameter of tumor was 5.7cm. Most tumors were presented as round or lobulated masses with well-demarcated margins. The solid portion of tumors showed slightly hypointense to isointense on T1WI, and isointense to slightly hyperintense on T2WI. Different cystic and necrotic portions within tumors were found in 13 patients, focal intratumoral hemorrhage were found in 2 patients. The tumors showed enhancement after contrast medium injection. Mild peritumoral edema was present. Ependymal or cerebrospinal dissemination was noted in 2 patients. On DWI, the solid portion of tumors showed heterogeneous isointense to hyperintense in 7 patients, homogeneous hyperintense in 4 patients, On ADC map, the solid portion of tumors showed hypointense in 9 patients, slightly hypointense in 2 patients. The average ADC values of the solid portion of tumors was 0.72×10-3mm2/s. The average ADC values of the normal contralateral white matter was 0.86×10-3mm2/s. There was statistically significant difference in mean ADC value between the solid portion of tumors and normal contralateral white matter（t=10.84，P<0.05）. On microscopic examination, the cellular tumors composed of round to oval small cells with hyperchromatic nuclei and frequent mitoses, the cytoplasm of tumor cells were scanty and ill-defined, The tumor cells were densely packed and arranged in cords or nests. Immunohistochemically, tumor with neuronal differentiation was reactive for synaptophysin(Syn), tumor with glial differentiation was reactive for glial fibrillary acidic protein(GFAP), most tumors exhibited both neuronal and glial bi-potential differentiation. Conclusions: The pathology of supratentorial PNET determine its characteristic appearance on conventional MRI and DWI, the hyperintensity on DWI and decreased ADC value within the solid portion of tumors is caused by their dense cellularity and high nuclear to cytoplasmic ratio.
2009, Vol. 20 
