Reactive thymic hyperplasia mimicking relapse in a child with post-treatment T-cell Non-Hodgkin's lymphoma: A case report and literature review

Background: Chemotherapy usually results in the premature shrinkage of thymic cells, often resulting in atrophy. However, in some children, the thymus has the potential to regenerate following the withdrawal of stimulus, resulting in an increase in thymic cells – called rebound/reactive thymic hyperplasia. This phenomenon often appears clinically and radiologically similar to lymphoma in the anterior mediastinum, leading to overtreatment. Case report: We report a 6-year-old boy with T-Lymphoblastic lymphoma (LL) who presented with mediastinal mass. He was treated with high risk ALL protocol and completed treatment uneventfully. Post-treatment PET-CT for routine assessment showed an anterior mediastinal mass with a SUVt of 4.64, highly suggestive of recurrence, however was finally diagnosed with thymic hyperplasia confirmed by biopsy. Conclusion: Pediatric hemato-oncologists and radiologists need to be aware of this phenomenon to avoid misdiagnosis and overtreatment. Relapse should always be confirmed by histopathological examination.