MEDB-77. Metastasic medulloblastoma: radiological features and its correlation with molecular subgroups and dissemination pattern

Medulloblastoma (MB) is the most frequent malignant childhood brain tumor. Four molecular subgroups have been described (WNT, SHH, group3, group4), which are associated with a different biological profile, prognosis, specific MRI characteristics and patterns of metastatic dissemination. We aimed to determine the imaging features of the metastatic MB and its molecular subgroup and their outcomes. Retrospective single-center analytic-observational study conducted from January 2004-January 2022 in a tertiary-care center. Pediatric patients with metastatic medulloblastoma at disease onset were included. We collected epidemiological and clinical characteristics, treatment received, and outcomes. The molecular subgroup was determined by its methylation profile. MRI were reviewed by the neuroradiologist. Sixty-three patients were diagnosed, 17 (26.9%) were metastatic. The median age at diagnosis was 5.1 years (range 2.1-17.5 years), 58.8% were male. According to histopathologic classification, fifteen patients (93.8%) were classic,1 (6.3%) desmoplastic. Molecular subgroup analysis showed 2 WNT (12.5%), 1 SHH (6.3%), 3 (18.8%) group 3 (G3) and 5 (31.2%) group 4 (G4). Four patients (25%) were classified as G3/G4 and 1 (6.3%) as mixed. Five patients (29.4%) were M2 and 12 patients (70.6%) were M3 according to Chang staging system. The location in the cerebellar hemispheres was only observed in SHH patient while G3 tumors presented homogeneous contrast enhancement. All WNT, G3 and G4 were located in IV ventricle. We found no association between molecular subgroup and metastatic site (intracranial vs spinal, Fisher test, p=0.45). All patients presented with metastasis in the third ventricular infundibular recess were G4. Four patients died, all of them were G3 or G3/G4. Our results supported the literature previously reported. According to the MRI imaging features, the molecular medulloblastoma subgroups could be suggested. The presence of metastasis in the infundibular recess suggested MB group 4. However, the dissemination pattern could not be associated with any subgroup in our series.