Teaching Case

The patient was admitted to the neurology department with complaints of severe headache for 3 months and loss of vision that developed abruptly. He had no significant previous medical history.

MRI study was performed with routine protocols and additional echo-planar diffusion-weighted imaging (DWI) was also obtained. An irregular-shaped lesion was detected which extended towards the uncal part of parahippocampal gyrus, optic radiation, hippocampus and occipital lobe. The lesion was representing hypointense signal intensity on T1-weighted images, high signal intensity on T2-weighted and FLAIR images. The lesion enhanced heterogeneously with gyral Gd-contrast. Echo-planar diffusion-weighted imaging of the lesion revealed a moderate degree of diffusion restriction. There was a small zone of surrounding oedema. The lesion seemed to be a vascular territory and for differential diagnosis spectroscopic study was performed. There was a large choline peak and reversed choline/creatinine ratio. NAA was decreased indicating neuronal loss. An additional increase in myoinositol peak was noted. Radiologic indications suggested the lesion to be a diffuse infiltrating tumour such as a glioma which is the most common differential diagnosis of an infarct; however, brain biopsy resulted dissimilar.

Primary CNS lymphomas are more common than secondary lymphomas and usually seen in adults above 40 years of age [1]. B-cell lymphomas are more common than T-cell lymphomas. There is an increasing incidence in population due to increasing number of immuncompromised patients. Intracranial lymphomas can involve the leptomeninges, being more common in secondary lymphomas than primary lymphomas. The deep basal ganglia, periventricular region and corpus callosum are common sites of involvement [2]. The lesions usually show hypointense signals on T1WI and hyperintense signals on T2WI with obvious nodular enhancement after gadolinium injection [3]. MRI features of primary and secondary lymphomas of brain overlap and stereotactic biopsy ensures a pathological proof. Differential diagnosis of primary CNS lymphomas includes glial tumours, toxoplasmosis, secondary involvement of systemic lymphoma and vascular territories. The mean survival time after medical treatment changes from 13 months to 2 years [4], showing that the prognosis of CNS lymphoma is poor. Some advanced techniques such as MR spectroscopy, diffusion-weighted and MR perfusion imaging, and scintigraphy are very helpful to reach the correct diagnosis because sometimes tumours, especially gliomas, mimic an infarct. In MR spectroscopy cerebral lymphomas show a large choline peak and reversed choline/creatinine ratio, a lactate peak may also be seen [5]. Increased lipid in the spectrum is considered to be a more reliable indicator in the differential diagnosis of primary central nervous system lymphoma and glial tumours as well [6]. MR perfusion shows only a modest increase in rCBV, much less marked than in high-grade gliomas, where angiogenesis is a prominent feature. In scintigraphy an increased Thallium 201 uptake is seen, and PET also shows an increased C11 Methionine uptake.