الفهرس 
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Abstract
Meningiomas are the most common primary brain tumor as well as the most common intradural spinal tumor.
Meningiomas are classified according to the WHO grading system into grade I,II and III. Over 80% of meningiomas are classified as WHO grade I while about 5-15% are classified as grade II and only 1-3% are of grade III.
Histology predicts mortality and recurrence, with atypical and malignant meningiomas having higher recurrence rates and shorter survival times than those with benign histology. The grade of a meningioma has important therapeutic and prognostic implications. Thus, prospectively identifying the histologic grade of a meningioma can be clinically beneficial.
Preoperative knowledge of an atypical meningioma may also change a neurosurgeon’s risk-benefit assessment.
Conventional MRI studies` cannot distinguish pathological types before surgery. The use of the conventional MRI limits the application of the MRI to the morphological information.
Diffusion-weighted magnetic resonance imaging is advanced MRI technique that provides image contrast that is different from that provided by conventional MR techniques. Diffusion weighted imaging allows us to assess the tumor cellularity non-invasively because cellular and subcellular elements significantly impede the mobility of water molecules, thus these densely cellular regions exhibit low ADC values.
This study aimed to assess the role of DWI and ADC values in grading of intracranial meningiomas
This study was conducted on twenty patients with either symptoms suggesting intracranial neoplasm or incidentally discovered extra-axial mass on CT.
It included fifteen females and five males. Their ages ranged between 26 and 72 years with a mean age of 51 years
All patients were subjected to full history taking, thorough clinical assessment and conventional MRI study of the brain with DWI. Then, histopathological assessment after surgical management is done. Fourteen cases were diagnosed as WHO grade I meningiomas and six cases as grade II meningiomas. No cases of grade III lesions were diagnosed.
Regarding the site of the lesion, convexity and parasagittal meningiomas were the most common seen in in ten cases (50%).
The most frequently encountered initial complaint was headache, seen in 11 cases (55% of patients).
Based on conventional MRI features, heterogeneous enhancement, irregular tumor margin and peritumoral edema were more encountered in grade II lesions as compared to grade I. However, a significant overlap was noted between both groups and none of these features were unique to grade II lesions.
Regarding the DWI, both grade I and grade II lesions showed variable signal intensity on DW images. On the other hand, intratumoral ADC values showed a significant difference between both groups with no overlap could be noted. The mean ADC value of grade I meningiomas was 1.02 +/- 0.16 x 10-3mm2/sec which was higher than that of grade II meningiomas; 0.68 +/- 0.04 x 10-3mm2/sec.
Therefore, DWI and ADC values should be considered a valuable MR sequence for differentiation between grades of meningiomas.