title: The diagnostic value of 18F-FDG PET and MRI in paediatric histiocytosis.
abstract: OBJECTIVE
  To analyse the diagnostic value of (18)F-FDG PET and MRI for the evaluation of active lesions in paediatric Langerhans cell histiocytosis.
  
  
  METHODS
  We compared 21 (18)F-FDG PET scans with 21 MRI scans (mean time interval 17 days) in 15 patients (11 male, 4 female, age range 4 months to 19 years) with biopsy-proven histiocytosis. Primary criteria for the lesion-based analysis were signs of vital histiocyte infiltrates (bone marrow oedema and contrast enhancement for MRI; SUV greater than the mean SUV of the right liver lobe for PET). PET and MR images were analysed separately and side-by-side. The results were validated by biopsy or follow-up scans after more than 6 months.
  
  
  RESULTS
  Of 53 lesions evaluated, 13 were confirmed by histology and 40 on follow-up investigations. The sensitivity and specificity of PET were 67 % and 76 % and of MRI were 81 % and 47 %, respectively. MRI showed seven false-positive bone lesions after successful chemotherapy. PET showed five false-negative small bone lesions, one false-negative lesion of the skull and three false-negative findings for intracerebral involvement. PET showed one false-positive lesion in the lymphoid tissue of the head and neck region and two false-positive bone lesions after treatment. Combined PET/MR analysis decreased the number of false-negative findings on primary staging, whereas no advantage over PET alone was seen in terms of false-positive or false-negative results on follow-up.
  
  
  CONCLUSIONS
  Our retrospective analysis suggests a pivotal role of (18)F-FDG PET in lesion follow-up due to a lower number of false-positive findings after chemotherapy. MRI showed a higher sensitivity and is indispensable for primary staging, evaluation of brain involvement and biopsy planning. Combined MRI/PET analysis improved sensitivity by decreasing the false-negative rate during primary staging indicating a future role of simultaneous whole-body PET/MRI for primary investigation of paediatric histiocytosis.
authors.affiliation: Department of Nuclear Medicine, Ludwig-Maximilians-University of Munich, Marchioninistraße 15, 81377, Munich, Germany. wolfgang.mueller@med.uni-muenchen.de
authors.forename: Wolfgang Peter
authors.initials: WP
authors.lastname: Mueller
authors.forename: Henriette Ingrid
authors.initials: HI
authors.lastname: Melzer
authors.forename: Irene
authors.initials: I
authors.lastname: Schmid
authors.forename: Eva
authors.initials: E
authors.lastname: Coppenrath
authors.forename: Peter
authors.initials: P
authors.lastname: Bartenstein
authors.forename: Thomas
authors.initials: T
authors.lastname: Pfluger
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D015614:Histiocytosis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000628:therapy; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging; D008297:Male; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D019788:Fluorodeoxyglucose F18