Susceptibility-weighted imaging and diffusion-weighted imaging findings in central nervous system monomorphic B cell post-transplant lymphoproliferative disorder before and after treatment and comparison with primary B cell central nervous system lymphoma.

The purpose of this article is to review the MRI features of monomorphic central nervous system post-transplant lymphoproliferative disorder (CNS PTLD), including diffusion-weighted and susceptibility-weighted sequences before and after treatment and to compare the imaging findings with those of primary central nervous system B cell lymphoma (PCNS BCL). Retrospective review of the brain MRI characteristics in patients with pathology proven monomorphic CNS PTLD and PCNS BCL was performed. In particular, the enhancement, diffusion-weighted, susceptibility-weighted MRI characteristics of the lesions were evaluated. In addition, the diffusion-weighted, susceptibility-weighted MRI features after treatment for CNS PTLD were evaluated. A total of 12 lesions in six patients with CNS PTLD and 12 lesions in nine patients with PCNS BCL were identified on MRI. Among the CNS PTLD lesions with post-contrast images, 80 % demonstrated peripheral enhancement. All of the CNS PTLD lesions contained foci of intratumoral susceptibility signal (ITSS) and the average mean ADC values and ratios were 0.892 × 10(-3) mm(2)/s (standard deviation: 0.082 × 10(-3) mm(2)/s) and 1.19 (standard deviation: 0.15), respectively. On the other hand, 75 % of the PCNS BCL displayed diffuse enhancement, two cases (16.7 %) contained ITSS, and the mean ADC values and ratios were 0.721 × 10(-3) mm(2)/s (standard deviation: 0.093 × 10(-3) mm(2)/s), and 0.99 (standard deviation: 0.17), respectively. Thus, the presence of heterogeneous lesions with ITSS that do not necessarily have as extensive restricted diffusion as PCNS BCL is suggestive of CNS PTLD in the appropriate clinical setting. The preliminary data in this series suggests that diffusion-weighted imaging may serve as a useful biomarker for monitoring treatment response, in which successful treatment of CNS PTLD may result in increased ADC values. In addition, foci of susceptibility effect in CNS PTLD tend to persist or increase over the course of treatment.