Purpose or Case Report: Purpose: ¹⁸F-FDG Positron Emission Tomography (PET-CT) has been shown to be superior to other imaging modalities in assessment of soft tissue involvement with Langerhans Cell Histiocytosis (LCH) and is now commonly included in the staging workup of LCH. Our purpose is to analyze the utility of skeletal survey in addition to PET-CT scan for detecting bone lesions in children with LCH and to evaluate if skeletal survey can be eliminated from the staging workup of LCH in order to reduce radiation exposure.
Methods & Materials: This is a retrospective study of patients with biopsy-confirmed LCH diagnosed and treated at a tertiary care children’s hospital between 2013 and 2018. The medical records, skeletal survey and PET-CT imaging records for staging and follow-up studies were reviewed. The distribution and number of LCH lesions on both skeletal survey and PET-CT were documented from our institution’s PACS. Any reports with insufficient information or ambiguity were re-evaluated by a Pediatric Radiologist. Demographic information was recorded and the concordance between lesions seen on the skeletal survey and/or PET-CT scan was calculated.
Results: Data from 10 children (60% female) with a median age of 4.6 years (range from 1 year 7 months to 15 years, 1 month) are reported. A total of 53 lesions in 40 different bones were evaluated. Forty-nine per cent of all lesions were identified on both PET-CT and skeletal survey. PET-CT identified an additional 34% of lesions not seen on skeletal survey, while skeletal survey identified 17% of lesions not seen on PET-CT. There were 9 calvarial lesions, all identified on skeletal survey while only 4/9 were identified on PET-CT scan. The median interval between the skeletal survey and PET-CT scan was 2.5 days (1-15 days).
Conclusions: Skeletal survey continues to be important in the evaluation of LCH patients, especially when assessing lesions involving the calvarium. This may, in part, be due to the thickness of the PET-CT slices reducing lesion conspicuity and the marked avidity of the brain parenchyma on PET-CT obscuring lesions within the calvarium.