Glioblastoma multiforme with atypical diffusion-weighted MR findings.

The aim of this study is to review the diffusion-weighted MRI findings of glioblastomas, to investigate those with atypical characteristics and to emphasise the reasons responsible for the atypical features on diffusion-weighted MR images. 48 cases of histologically proven glioblastomas were included in this study. In addition to conventional sequences of routine tumour protocol, diffusion-weighted MRI with spin-echo echo-planar sequence was performed. The cystic-necrotic components of the lesions, according to the conventional sequences, were determined on the diffusion-weighted MR images and were classified as typical or atypical. The presence of high signal intensity was accepted as an atypical feature while low signal intensity was accepted as typical. The apparent diffusion coefficient (ADC) values of the cystic components were calculated. The statistical significance of the typical and atypical glioblastomas was evaluated with the students t-test. In six of the cases apparent high signal intensity in diffusion weighted MR images was interpreted. In three cases the high signal intensity occupied all of the cystic component and in the other three most of the cystic component. The ADC values of the lesions varied between 0.86 x 10(-3) mm(2) s(-1) and 1.39 x 10(-3) mm(2) s(-1) (mean value 1.06+/-0.17 x 10(-3) mm(2) s(-1)). In 42 of the lesions the cystic-necrotic component demonstrated low signal intensity and the ADC values varied between 1.56 x 10(-3) mm(2) s(-1) and 3.32 x 10(-3) mm(2) s(-1) (mean value 2.36+/-0.46 x 10(-3) mm(2) s(-1)). The difference between ADC values of atypical and typical lesions was statistically significant (p<0.001). The vast majority of glioblastomas do not exhibit restricted diffusion in diffusion-weighted MRI, but some of them display homogeneous or heterogeneous high signal intensity and decrease of ADC values. Diffusion-weighted MRI alone is not helpful in the differentiation of malignant tumours from abscesses with low ADC values and similar conventional MRI findings.