MR Imaging Characteristics of Wingless-Type-Subgroup Pediatric Medulloblastoma.

BACKGROUND AND PURPOSE: "Transcriptionally different" medulloblastoma groups are associated with specific signaling pathway abnormalities; hence, they may present with distinct imaging manifestations. In this study, we sought to describe the MR imaging features of wingless-type-subgroup medulloblastomas with embryologic correlations.

MATERIALS AND METHODS: Pre- and postoperative imaging studies of 16 patients with wingless-type-subgroup medulloblastoma were evaluated for tumor location, involvement of surrounding CSF spaces or parenchymal structures, conventional and DWI signal properties, and postsurgical damage patterns. Laterality scores were assigned to tumors at each step in the evaluation process. Continuous variables were summarized by using descriptive statistics. The Wilcoxon signed rank test was performed to compare laterality scores. To determine the interobserver variability, we computed the intraclass correlation and Cohen κ coefficients.

RESULTS: Wingless-type-subgroup medulloblastomas in our series were histopathologically "classic." Wingless-type-subgroup medulloblastomas occur in specific sites, with involvement of the foramen of Luschka (75%), the fourth ventricle (68.75%), the cisterna magna (31.25%), and the cerebellopontine angle cistern (18.75%). Laterality scores were low (<2) when preoperative primary and secondary anatomic features were evaluated separately, but they increased (>2) when all pre- and postoperative anatomic features were considered. Results were statistically shown to be reproducible (interclass correlation coefficient, 0.71-0.94; Cohen κ, 0.63-1.00). On the basis of anatomic lesion patterns, 4 location-based subtypes may be distinguished: 1) midline-intraventricular, 2) midline-extraventricular, 3) off-midline-intraventricular, and 4) off-midline-extraventricular, which represent a continuum.

CONCLUSIONS: Wingless-type-subgroup medulloblastomas are lateralized tumors arising from the brain stem and cerebellum around the foramen of Luschka. Our current understanding of their embryologic origins is in concordance with the spatial distribution of these tumors.