“…Here, we present the case of a 10-year-old immunocompetent male with evolution of ALK-1-positive anaplastic T-cell lymphoma on MRI, visualized over 24 days with four MRIs. Despite numerous descriptions of radiographic features of PCNSL in immunocompetent patients, there has been no documentation of a PCNSL evolving so rapidly on serial imaging [6,7,9,11,12,13,25,26,27,28,29,30,31,32,33,34]. …”