Schwannomas or neurilemomas are reasonly common benign nerve sheath tumors that can affect most if not all peripheral nerves.  They are in general FDG avid and should be included in the differential of mass lesions detected on PET.  There is unfortunately no correlation between avidity and aggressiveness i.e. the presence of marked FDG uptake (high SUV > 6) does not necessarily indicate a malignant nerve cell tumor.