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Figure 58.1 An example of the MRI features of PCNSL. Pre- and postgadolinium T1 MRI images showing an isodense lesion in the region of the left basal ganglia and thalamus. There is a mass effect with compression of the left lateral ventricle and moderate surrounding edema. The lesion enhances homoge-nously postcontrast progressive focal neurological deficits or, if the frontal lobes are involved or there is diffuse parenchymal infiltration, cognitive and behavioral abnormalities.12 Unlike other primary brain tumors, seizures are uncommon, because PCNSL usually affects subcortical structures.

Central structures apart from the brain parenchyma are often affected. The eye itself is a direct extension of the brain, and 10-20% of patients with PCNSL have ocular involvement at diagnosis.1314 Ocular lymphomas can involve the vitreous, retina, choroid, or optic nerve itself, and cause blurred vision, floaters, or maybe clinically silent. The process may begin unilaterally, but eventually bilateral involvement develops. The majority of patients, who present with ocular lymphoma alone, will eventually develop cerebral involvement. Concomitant involvement of the leptomeninges can be seen in 15% of patients, but is rarely the sole site of disease.

Several large retrospective studies have described the clinical characteristics of patients with PCNSL.51516 The median age at diagnosis is about 60 years, with a wide range of 12-85 years. There is a slight male predominance, and two-third of patients present with a poor performance status. One-third of patients have elevated serum lactate dehydrogenase (LDH). One-third of patients have involvement of deep structures, including the cerebellum, basal ganglia, corpus callosum, and brain stem. Brain lesions are multifocal in 30-40% of patients, and even when the tumor is seemingly localized by MRI, microscopic disease involves radiologically normal brain tissue at autopsy.17 Therefore, PCNSL should be considered disseminated within the CNS at diagnosis.

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