Abstract Background Distinguishing radiation-induced necrosis (RIN) from true tumor progression in pediatric embryonal brain tumors (PEBT) treated with high-dose chemotherapy (HDC) and radiation (RT) remains challenging,as misinterpretation may lead to unnecessary interventions. We report the clinical and MRI features of pseudoprogression in this population. Methods This retrospective case series identified radiological pseudoprogression in 8 of 28 PEBT patients treated with HDC/autologous stem cell transplantation and RT between July 2018 and January 2026. Clinical features, radiotherapy regimen, and MRI manifestations were summarized. Results Eight patients (median age, 34.5 months; range, 11.9–81.4) with PEBT (6 atypical teratoid/rhabdoid tumors, 2 embryonal tumors with multilayered rosettes) were included. Five patients received craniospinal irradiation and 3 focal radiotherapy. RT modalities included proton (n = 4) and photon therapy (n = 4), delivered either before (n = 6) or after HDC (n = 2). Pseudoprogression manifested at a median of 6 months (range, 0.6–11) after RT initiation. Motor deficits were the most prevalent symptoms (n = 5). All lesions occurred within the boost field, with multifocal involvement in 7 patients. Predominant sites included the thalamus (62.5%), basal ganglia, temporal lobe, pons, and cerebellar hemispheres (50% each). Key MRI features included absence of restricted diffusion in all cases, and perilesional edema (n = 6). MR spectroscopy (n = 3) demonstrated prominent lactate/lipid peaks, and perfusion MRI (n = 3) showed hypoperfusion, supporting necrosis. Median time to lesion regression was 135.5 days (range, 46–651), with earlier regression observed in patients managed with treatment de-escalation strategies (46–68 days; n = 3). With a median follow-up from tumor diagnosis of 30 months (range, 10.1–39.4), 7 patients had no evidence of disease. Conclusions Pseudoprogression in PEBT typically presents as multiple enhancing lesions within the radiation field approximately 6 months post-RT. Absence of restricted diffusion, perilesional edema, and necrosis are characteristic features to differentiate RIN from tumor progression, preventing overtreatment.
Lin et al. (Tue,) studied this question.