MRI in primary malignant lymphomas of the brain

We evaluate the characteristics of MRI findings in 5 cases of malignant lymphomas of the brain which was surgically verified. The MRI findings are compared with those of CT scan. Malignant lymphoma was demonstrated as a mass of iso or high density surrounded by a low density area on CT scan. The demarcation was fine in two cases and poor in 3 other cases. It was markedly enhanced with contrast medium in all cases. Malignant lymphoma was delineated as a poorly defined mass of low signal intensity on T1-weighted image of MRI, and as a well defined mass a moderately high signal intensity or a mixture with iso signal intensity on T2-weighted image whereas the perifocal edema was an area of markedly high signal intensity. T1-gadolinium image intensified the signal of the mass specifically. As those, extent of the tumor was better delineated on T1-gadolinium image and extent of the perifocal edema on T2-weighted image. The size of the tumor delineated on T2-weighted and T1-gadolinium images was larger than that on enhanced CT scans. As a conclusion, the diagnosis of malignant lymphoma of the brain is not always definitive on CT scan. On the other hand, it has become much easier and more accurate with MRI. (author)