RETURN TO ABSTRACT LISTING


Background
Primary CNS lymphoma (PCNSL) is a subtype of extranodal non-Hodgkin lymphoma. It is an uncommon variety, with an incidence of only 0.47 per 100,000 people. The more common involvement of the CNS in lymphoma is through secondary deposits, which may be within the brain parenchyma as well as in the meninges. PCNSL usually presents as solid lesions that are hyperdense on CT, hypointense on T2-weighted images, iso to hypointense on T1-weighted images, and show restricted diffusion along with diffuse postcontrast enhancement. However, occasionally PCNSL presents with atypical findings, making the diagnosis challenging. The lesions may appear as noncontrast enhancing areas of signal abnormality or can present as diffuse disease with multifocal involvement, mimicking other disease processes, such as infection or demyelination rather than PCNSL. Other atypical features include hemorrhage, calcification, cyst, and necrosis within the lesions. An understanding of the differentiating features and identification of features pertinent to lymphoma is crucial for adequate diagnosis and treatment.

Educational Goals / Teaching Points
1. Get acquainted with different patterns of atypical lymphoma. 2. Suggest a search pattern to approach the diagnosis. 3. Enlist top differentials diagnosis with imaging features.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The usual presentation of primary CNS lymphoma is that of solid enhancing T2 hypointense lesions characteristically in a periventricular location. However, primary CNS lymphoma may also present as multifocal nonconfluent, nonenhancing lesions, lesions involving brainstem with nodular enhancement, and lesions showing susceptibility. This exhibit will elaborate the role of MRI as a diagnostic tool in primary CNS lymphoma. The use of DWI is invariable in cases of CNS lymphoma. Diffusion restriction in the lesions has been related to high proliferative activity. This text will also discuss role of advanced MRI options, such as spectroscopy and perfusion studies, and the role of other modalities, such as CT and PET/CT. The exhibit will also discuss the characteristic histopathological findings of CNS lymphoma.

Conclusion
The appearance of PCNSL is changing, and conventional knowledge is not enough to make the correct diagnosis. PCNSL can present as a multitude of imaging findings. One should be aware of these atypical features and consider PCNSL as a possible diagnosis in the absence of usual imaging appearance.