Primary diffuse large B-cell lymphoma of the CNS

Within the medial aspect of the left temporal lobe, there is an intra-axial lesion which is mildly hyperdense to parenchyma on non-contrast imaging and demonstrates relatively homogeneous enhancement. There is associated extensive surrounding hypodensity that extends anteriorly into the left temporal lobe as well as superiorly adjacent to the trigone of the left lateral ventricle. There is entrapment of the temporal horn of the left lateral ventricle secondary to this mass as well as some regional sulcal effacement. 

There is an intra-axial mass in a periventricular location within the medial aspect of the left temporal lobe that is slightly hypointense on T2 to cortex and demonstrates homogeneous enhancement . A smaller enhancing nodule anterolaterally is also noted. The enhancing components demonstrate high signal on DWI with ADC values of approximately 720 x 10-6/s. No associated blooming on susceptibility weighted imaging. No associated increased CBV. Spectroscopy demonstrates marked reduction of NAA as well as reversal of the choline to creatine peak. 

There is surrounding T2/ FLAIR white matter hyperintensity that extends anteriorly through the left temporal lobe as well as into the posterolateral margin of the left thalamus. There is again entrapment of the temporal horn of the left lateral ventricle and mild associated regional positive mass effect. No other intra-axial mass.

Conclusion: Left medial temporal mass in a periventricular location has MR and CT features that strongly suggest CNS lymphoma. Metastatic disease and glioblastoma are unlikely.