Differentiation between rebound thymic hyperplasia and thymic relapse
after chemotherapy in pediatric Hodgkin lymphoma
Abstract
Background Rebound thymic hyperplasia (RTH) is a common
phenomenon caused by stress factors such as chemo- (CTX) or radiotherapy
with an incidence of up to 40%. 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 CTs and 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 FDG-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 a new or growing mass in the thymic space
occurred in 133 of 291 patients. Without biopsy only 100 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 (34/35). All RTH patients (65/65) 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, an isolated thymic mass after
CTX likely represents RTH.