BACKGROUND: Rebound thymic hyperplasia (RTH) is a common phenomenon caused by stress factors such as chemotherapy (CTX) or radiotherapy, with an incidence between 44% and 67.7% in pediatric lymphoma. Misinterpretation of RTH and thymic lymphoma relapse (LR) may lead to unnecessary diagnostic procedures including invasive biopsies or treatment intensification. The aim of this study was to identify parameters that differentiate between RTH and thymic LR in the anterior mediastinum. METHODS: After completion of CTX, we analyzed computed tomographies (CTs) and magnetic resonance images (MRIs) of 291 patients with classical Hodgkin lymphoma (CHL) and adequate imaging available from the European Network for Pediatric Hodgkin lymphoma C1 trial. In all patients with biopsy-proven LR, an additional fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT was assessed. Structure and morphologic configuration in addition to calcifications and presence of multiple masses in the thymic region and signs of extrathymic LR were evaluated. RESULTS: After CTX, a significant volume increase of new or growing masses in the thymic space occurred in 133 of 291 patients. Without biopsy, only 98 patients could be identified as RTH or LR. No single finding related to thymic regrowth allowed differentiation between RTH and LR. However, the vast majority of cases with thymic LR presented with additional increasing tumor masses (33/34). All RTH patients (64/64) presented with isolated thymic growth. CONCLUSION: Isolated thymic LR is very uncommon. CHL relapse should be suspected when increasing tumor masses are present in distant sites outside of the thymic area. Conversely, if regrowth of lymphoma in other sites can be excluded, isolated thymic mass after CTX likely represents RTH.

Department Department of Pediatric Radiology University Bielefeld Campus Bielefeld Bethel Bielefeld Germany

Department of Clinical Radiology University Hospital of Münster Münster Germany

Department of Medical Oncology and Radiotherapy Oslo University Hospital Oslo Norway

Department of Nuclear Medicine University of Leipzig Leipzig Germany

Department of Paediatric Oncology Royal Hospital for Sick Children University of Edinburgh Edinburgh UK

Department of Pediatric Hematology and Oncology Justus Liebig University Gießen Germany

Department of Pediatric Hematology and Oncology National Institute of Paediatric Diseases Bratislava Slovakia

Department of Pediatric Hematology and Oncology St Anna Children's Hospital Medical University of Vienna Vienna Austria

Department of Pediatric Hematology and Oncology University Hospital Motol and 2nd Medical Faculty of Charles University Prague Czech Republic

Department of Pediatric Hematology and Oncology University Hospitals Leuven Leuven Belgium

Department of Radiation Oncology Medical Faculty of the Martin Luther University Halle Germany

Department of Radiation Oncology University Hospital Vienna Vienna Austria

Department of Radiology Diakoniekrankenhaus Halle Halle Germany

Department of Radiology University Hospital Halle Germany

Division of Pediatrics Department of Woman Mother Child Pediatric Hematology Oncology Unit University Hospital of Lausanne and University of Lausanne Lausanne Switzerland

Erasmus MC Sophia Children's Hospital Rotterdam The Netherlands

Institute of Medical Informatics Statistics and Epidemiology University of Leipzig Leipzig Germany

Karolinska University Hospital Astrid Lindgrens Childrens Hospital Stockholm Sweden

Pediatric Onco Hematology Unit Hospital Universitario Virgen Macarena Sevilla Spain

Pediatric Oncology and Hematology Department University Children's Hospital of Krakow Krakow Poland

Princess Màxima Center for Pediatric Oncology Utrecht The Netherlands

Service d'Hématologie Pédiatrique Hôpital Robert Debré Paris France

Sorbonne Université APHP hôpital Trousseau Paris France

Pediatr Blood Cancer. 2023 Oct;70(10):e30492. doi: 10.1002/pbc.30492. PubMed

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