Comparative MR Study Of Different Grades Of Astrocytomas And Metastatic Brain Tumors

Objective:The aim of this study is to determine whether MR (Magnetic Resonance) signal intensities and ADC (Apparent Diffusion Coefficient) values have any significance in differentiating astrocytomas and metastatic brain tumors.Materials and Methods:Total of 56 cases of brain tumors (14 cases of low-grade,22 of high-grade astrocytomas and 20 of metastases) were selected retrospectively. All the cases were in the period between January 2007 and Feb 2010. The patients'clinical data, pathological diagnosis and grading of the astrocytomas were recorded along with presenting complaints.MRI scans were done using GE Signa HD1.5T/iMR imager (USA). The scan sequences included conventional scans, gadolinium enhanced T1 weighted images and Diffusion Weighted Images.The characteristics of tumor based on its location, size, irregularity, peripheral edema and contrast enhancement were recorded initially. Peripheral edematous area was divided into immediate and distant areas (＜0.5cm and＞0.5cm from the tumor margin). The area of necrosis of the tumor was grouped into solid and where the tumor had necrosis of＜50%and＞50%.In later analysis the MR intensity and ADC values were measured for the T1 weighted images of the tumor area, peripheral edema area 1 and 2 and the corresponding contra lateral normal brain area before the introduction of contrast agent and again after introducing the contrast agent. The differences of MR intensities between pre and post contrast scans were calculated. The ratio of these differences to that of pre contrast T1WI scans were calculated and were analyzed. The ratio of ADC values between the lesion and normal white matter were calculated and analyzed.The statistical analysis was made using the SPSS 11.5 version. While calculating between two groups, independent T test was used and while comparing between two groups of astrocytomas and metastases, one-way Annova was used. The location, size, margin were compared using chi-square tests. P＜0.05 was considered significant.Results:1. Morphological differences:There was no significant difference in the occurrence of tumor with regard to gender or age. Astrocytomas were found more in the frontal lobe whereas metastases did not show any predilection to the location. Astrocytomas were comparatively larger than metastases. There was no difference in the extent of the edema between astrocytomas and metastasis. Metastases had clear margin compared to astrocytomas and low grade astrocytomas had clear margin compared to high grade astrocytomas.2. Difference in MR intensity:The difference of the MR intensities (pre and post contrast scans) in the peripheral edema area of the astrocytoma and the metastasis did not show any significant difference whereas the MR intensity difference were higher in low grade astrocytomas than high grade astrocytomas when measured in the distant peripheral edematous area.3. Difference in the ADC values:The ratio of the ADC values between the peripheral edematous area of lesion and the contralateral normal side when calculated showed that the ratios were higher in the immediate peripheral edematous area surrounding the metastasis than astrocytomas. It also showed that the ADC value ratios were higher in metastasis in the distant peripheral edema area when compared between metastasis and high grade astrocytomas. Conclusion:Our research showed that differences in the MR signal intensities (post and pre contrast scans) were not statistically different between metastasis and astrocytomas whereas they were significantly different between low and high grade astrocytomas when measured in distant peripheral edematous area. Low grade astrocytomas had higher MR signal intensity.The ratio of the ADC values on the other hand were not useful in differentiating low and high grade astrocytomas, whereas it was significant in differentiating astrocytomas and metastatic brain tumors. The ADC value ratios were higher in metastasis than in both low and high grade astrocytomas when measured in the immediate peripheral area. It was also high in metastasis when compared between metastasis and high grade astrocytomas in distant peripheral edematous area.