Purpose or Case Report: Determine the incidence of occult malignancy detected by ¹⁸F-FDG PET-CT and whole body (WB) MRI in children.
Methods & Materials: IRB-approved retrospective review of ¹⁸F-FDG PET-CT and WB MRI studies performed on pediatric patients ages 0 to 18 years between February 2005 and August 2016 for the indication of suspected occult malignancy. Keywords for database search included: “anti-NMDA receptor encephalitis,” “unknown malignancy,” “Lambert-Eaton,” “paraneoplastic,” “occult malignancy,” “possible malignancy.” Patients were excluded if their prior clinical history included a concern for rheumatologic abnormality, known primary or prior mass, solid organ or bone marrow transplantation, lymphadenopathy including PTLD, bone marrow abnormality, or brain/spinal cord lesion. The imaging studies and imaging reports were reviewed and classified as positive, negative or equivocal. All equivocal studies had follow-up studies or clinical notes that were available to determine whether they were truly positive for malignancy.
Results: 21/37 pediatric patients met the inclusion criteria (12 girls, 9 boys; mean age 10.4 years; range 0.2-18 years), 14 patients underwent ¹⁸F-FDG PET-CT and 7 patients underwent WB MRI. 18 of the studies were negative without any hypermetabolic abnormality or anatomic mass.. In addition, 3 studies with initially equivocal findings on WB imaging had follow up studies or subsequent clinical course that failed to reveal an underlying malignancy.
Conclusions: No occult malignancy was detected at our institution using whole body PET-CT or MR imaging calling into question its utility. If imaging is still pursued in the quest to uncover an underlying malignancy (usually for a suspected pediatric paraneoplastic syndrome), whole body MRI should be considered as a radiation free alternative.