Paraneoplastic encephalitis associated with cystic teratoma is detected by fluorodeoxyglucose positron emission tomography with negative magnetic resonance image findings.

The role of fluorodeoxyglucose (FDG) positron emission tomography (PET) as a functional imaging technique used in the evaluation of a variety of malignancies has been well known. Paraneoplastic encephalitis is a rare central nervous complication, which has been reported in some tumors. Traditionally, magnetic resonance imaging of the brain is performed to aid in its diagnosis. The authors report a case of paraneoplastic encephalitis, associated with cystic teratoma, which had positive FDG-PET findings but appeared normal on magnetic resonance imaging.