18 year-old male with history of CNS PTLD. Evaluate disease response following 5 cycles of methotrexate.RADIOPHARMACEUTICAL: 6.0 mCi F-18 fluorodeoxyglucose (FDG)BLOOD GLUCOSE (FASTING): 78 mg/dL Today's CT portion grossly demonstrates right posterior parietal burr hole with right high-density focus in the posterior parietal lobe which is similar in appearance compared to the recent diagnostic CT and may represent thrombosed vessel versus blood products. Additionally, there is bilateral vasogenic edema which is not significantly changed.Today's PET examination demonstrates the following: along the posterior and inferior aspect of the right parietal lobe, medial to the right lateral ventricular atrium, there is a medium sized region of markedly hypermetabolic focus consistent with active PTLD. This focus is anteromedially adjacent to but separate from the right posterior parietal high signal focus that was demonstrated on the MRI examination. The hypermetabolic right parietal lobe lesion corresponds to a very subtle area of enhancement seen on the recent MRI exam. Additionally, there is subtle heterogeneously diffuse foci of hypermetabolic activity along the leptomeninges of both hemispheres, suspicious for additional PTLD involvement. Bilateral basal ganglia and medial aspects of the inferior cerebellum demonstrate symmetric increased relative activity compared to the remainder of the cerebrum and the cerebellum. This is of uncertain etiology although given the uniform and symmetric activity, this is unlikely to be PTLD and may be related to methotrexate treatment.
1.Right posterior parietal hypermetabolic focus consistent with active PTLD. Of note, this hypermetabolic focus is adjacent to but separate from the high signal lesion noted on the recent MRI examination.2.Additional findings highly suspicious for with diffuse additional leptomeningeal tumor involvement bilaterally.