Purpose:To investigate the contribution of perfusionweighted MR imaging (PWI) by using the relative cerebral blood volume (rCBV) ratio in the differential diagnosis of various intracranial space-occupying lesions. Materials and Methods:This study involved 105 patients with lesions (high-grade glioma (N ϭ 26), low-grade glioma (Nϭ 11), meningioma (N ϭ 23), metastasis (N ϭ 25), hemangioblastoma (N ϭ 6), pyogenic abscess (N ϭ 4), schwannoma (N ϭ 5), and lymphoma (N ϭ 5)). The patients were examined with a T2*-weighted (T2*W) gradient-echo singleshot EPI sequence. The rCBV ratios of the lesions were obtained by dividing the values obtained from the normal white matter. Statistical analysis was performed with the Mann-Whitney U-test. A P-value less than 0.05 was considered statistically significant. Results:The rCBV ratio was 5.76 Ϯ 3.35 in high-grade gliomas, 1.69 Ϯ 0.51 in low-grade gliomas, 8.02 Ϯ 3.89 in meningiomas, 5.27 Ϯ 3.22 in metastases, 11.36 Ϯ 4.41 in hemangioblastomas, 0.76 Ϯ 0.12 in abscesses, 1.10 Ϯ 0.32 in lymphomas, and 3.23 Ϯ 0.81 in schwannomas. The rCBV ratios were used to discriminate between 1) high-and low-grade gliomas (P Ͻ 0.001), 2) hemangioblastomas and metastases (PϽ 0.05), 3) abscesses from high-grade gliomas and metastases (P Ͻ 0.001), 4) schwannomas and meningiomas (P Ͻ 0.001), 5) lymphomas from high-grade gliomas and metastases (P Ͻ 0.001), and 6) typical meningiomas and atypical meningiomas (P Ͻ 0.01).Conclusion: rCBV ratios can help discriminate intracranial space-occupying lesions by demonstrating lesion vascularity. It is possible to discriminate between 1) high-and low-grade gliomas, 2) hemangioblastomas and other intracranial posterior fossa masses, 3) abscesses from highgrade gliomas and metastases, 4) schwannomas and meningiomas, 5) lymphomas and high-grade gliomas and metastases, and 6) typical and atypical meningiomas.

Diffusion-weighted MR imaging findings of atypical/malignant meningiomas and typical meningiomas differ. Atypical/malignant meningiomas have lower intratumoral ADC values than typical meningiomas. Mean ADC values for peritumoral edema do not differ between typical and atypical meningiomas.

Differentiating meningiomas with atypical conventional MRI findings from malignant intraaxial tumors can be difficult. Calculation of rCBV ratios and construction of signal intensity-time curves may contribute to the differentiation of meningiomas from intraaxial tumors.

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.

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