The role of PET-CT in the differential diagnosis of thymic mass after treatment of patients with lymphoma

Abstract

Thymic hyperplasia is a common phenomenon in both children and young adults after chemotherapy and may explain the finding of a mediastinal mass in patients with malignant lymphoma after complete remission. In the present study, we report 5 cases with malignant lymphoma presenting with a mediastinal mass on CT scan after completion of chemotherapy diagnosed as thymic hyperplasia by PET-CT imaging. We retrospectively analyzed 5 patients who presented with anterior mediastinal masses a median of 4 months (range 3-6) after achieving complete remission following successful treatment for malignant lymphoma. Three patients were diagnosed with Hodgkin's lymphoma (HL) and the others with non-Hodgkin's lymphoma (NHL). The median age of the patients was 23 (range of 18-47). PET-CT was performed on these patients to determine the characteristics of a mass which had been detected on CT. PET-CT was performed for all patients, and the thymic masses demonstrated only mild FDG uptake considered to be consistent with thymic hyperplasia. During a median of 24 months of follow-up, all patients were recurrence-free with a median survival of 15 months (range 10-26 months). It is important to be aware of the possibility of thymic hyperplasia after chemotherapy to avoid misdiagnosis or over-staging of disease, as well as unnecessary biopsies, especially when the presenting anterior mediastinal mass was originally located near the thymus on CT scan. Mild FDG PET uptake was sufficient for the diagnosis of benign disease in the cases in this study.

Differentiation of Normal Thymus from Anterior Mediastinal Lymphoma and Lymphoma Recurrence at Pediatric PET/CT

“…In Table 5 Mean SUV t and SUV b of All Groups during Prechemotherapy, End of Chemotherapy, and Postchemotherapy Periods ( 5 ), or in 11.7% ( n = 120) of young adults with malignant testicular teratoma ( 28 ). In addition, we found thymic rebound at 10 months after the end of chemotherapy in children with lymphoma, while others described thymic rebound at 1-8 months after chemotherapy in children with nonHodgkin lymphoma ( 27 ), at 3-6 months after treatment of adults with malignant lymphoma ( 29 ), and at 3-14 months after chemotherapy in adult patients with malignant testicular teratoma ( 28 ). Smith et al ( 30 ) reported a superior mediastinal thymic extension associated with postchemotherapy thymic hyperplasia in 12% of 93 FDG PET/CT examinations.…”

Whole-body diffusion magnetic resonance imaging in the assessment of lymphoma

“…Recently we noticed in one patient at the end of therapy that the post-treatment inflammatory process may result in false-positive findings on diffusion MRI and FDG-PET/CT owing to macrophage proliferation. Diffusion MRI may also help in differentiating anterior mediastinal residual or recurrent tumour from benign thymic rebound, which is common in both children and young adults after chemotherapy [ 23 ] (Fig. 6).…”

¹⁸F-FDG PET/BT ile Anterior Mediastinal Kitlelerin Metabolik Karakterizasyonu

“…The most important change in the patients’ management was observed in the lymphoma group since the biopsy sites were altered due to the PET results. In a case series on patients with lymphoma, it was suggested that mild 18 F-FDG accumulating lesions in the anterior mediastinal region may indicate benign lesions like thymic hyperplasia even in lymphoma patients ( 14 ). However, in the case of the presence of diagnostic criteria indicating malignancy in lymphoma patients, secondary malignant tumors of the anterior mediastinum have been indicated in previous case reports ( 15 ).…”