title: Differentiation of normal thymus from anterior mediastinal lymphoma and lymphoma recurrence at pediatric PET/CT.
abstract: OBJECTIVE
  To evaluate the role of positron emission tomography (PET)/computed tomography (CT) in the differentiation of normal thymus from mediastinal lymphoma and lymphoma recurrence in pediatric patients.
  
  
  METHODS
  The study was approved by the institutional review board, and informed consent was waived. The study was HIPAA compliant. Two hundred eighty-two fluorine 18 fluorodeoxyglucose PET/CT studies in 75 pediatric oncology patients were reviewed retrospectively. Patients were divided into four groups: anterior mediastinal lymphoma (group A, n=16), anterior mediastinal lymphoma with subsequent recurrence (group B, n=5), lymphoma outside the mediastinum (group C, n=16), and other malignant tumors outside the thymus (group D, n=38). Analyses included measurements of the maximum anteroposterior and transverse dimensions of the anterior mediastinal mass or thymus on axial CT images and measurements of maximum standardized uptake values of anterior mediastinal mass, thymus (SUVt), and bone marrow at the level of the fifth lumbar vertebra (SUVb) on PET images. Quantitative parameters were compared by using an analysis of variance test.
  
  
  RESULTS
  Mean prechemotherapy SUVt was 4.82 for group A, 8.45 for group B, 2.00 for group C, and 2.09 for group D. Mean postchemotherapy SUVt for group B was 4.74. Thymic rebound (mean SUVt, 2.89) was seen in 44% of patients at a mean interval of 10 months from the end of chemotherapy. The differences between prechemotherapy SUVt of mediastinal lymphoma and normal thymus and postchemotherapy SUVt of lymphoma recurrence and thymic rebound were highly significant (P<.001).
  
  
  CONCLUSIONS
  SUVt is a sensitive predictor for differentiation of normal thymus or thymic rebound from mediastinal lymphoma. SUVt of 3.4 or higher is a strong predictor of mediastinal lymphoma.
authors.affiliation: Department of Radiology, Stanford University School of Medicine, and Pediatric Radiology Section, Lucile Packard Children's Hospital, 725 Welch Rd, Stanford, CA 94305-5654, USA.
authors.forename: Rakhee S
authors.initials: RS
authors.lastname: Gawande
authors.forename: Aman
authors.initials: A
authors.lastname: Khurana
authors.forename: Solomon
authors.initials: S
authors.lastname: Messing
authors.forename: Dong
authors.initials: D
authors.lastname: Zhang
authors.forename: Rosalinda T
authors.initials: RT
authors.lastname: Castañeda
authors.forename: Robert E
authors.initials: RE
authors.lastname: Goldsby
authors.forename: Randall A
authors.initials: RA
authors.lastname: Hawkins
authors.forename: Heike E
authors.initials: HE
authors.lastname: Daldrup-Link
mesh_terms: D000293:Adolescent; D002648:Child; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008223:Lymphoma / Q000175:diagnosis*; D008297:Male; D008479:Mediastinal Neoplasms / Q000175:diagnosis*; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis*; D049268:Positron-Emission Tomography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D013950:Thymus Gland / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*