MRI and FDG PET/CT Uncovered the Cause of a Paraneoplastic Leukemoid Reaction.

An 18-year-old man with progressive headache and vomiting for 2 weeks had significantly elevated levels of WBC count, which kept on rising over time during in-hospital evaluation. Exhaustive examinations did not reveal infection or any other explanations of increased WBC count. Instead, brain MRI and FDG PET/CT identified a malignant lesion in the brain without abnormality elsewhere. The pathological examination revealed a rhabdoid meningioma. The level of the WBC counts returned to normal promptly after surgical resection of the tumor, which confirmed the diagnosis of paraneoplastic leukemoid reaction.