The current World Health Organization classification of the central nervous system (CNS) has been expanded to include entities such as hematopoietic and lymphoid tumors (lymphomas and histiocytic tumors). Magnetic resonance imaging (MRI) is the preferred method of neuroimaging for diagnosing brain tumors, but standard MRI sequences for primary CNS lymphomas reveal findings similar to those for malignant gliomas, brain metastases, or inflammatory diseases. Advanced MRI sequences such as DWI, ADC, and perfusion can aid the diagnosis of PCNSL, but there is no clear evidence of their added value in treatment monitoring. PET imaging plays a complementary role in evaluating brain tumors, with radiolabeled amino acids being favored over [18F]fluorodeoxiglucose (FDG-PET). However, FDG-PET shows a high affinity for lymphomas, including PCNSL, which makes it particularly useful for diagnosis and assessing treatment responses.