MRI Differentiation of Anaplastic Ependymoma and Medulloblastoma with Fourth Ventricular Outlet Extension in Children.

PURPOSE: Medulloblastoma and anaplastic ependymoma (AE) are common malignant pediatric posterior fossa tumors with differing outcomes. While tumor extension through the fourth ventricular outlets (TETFVO) is common in AEs, it also occurs in some medulloblastomas, which complicates diagnosis. This study aimed to improve pretreatment differentiation between medulloblastomas with TETFVO and AEs for better treatment planning and outcome prediction. METHODS: From 2005 to 2024, we retrospectively analyzed 21 pediatric AE patients and 36 patients with medulloblastoma with TETFVO, assessing clinical data and MRI features, including lesion signals, intratumoral morphologies, and peritumoral/distal involvement. RESULTS: Compared with medulloblastomas with TETFVO, AE patients had a significantly higher tumor recurrence/progression rate (p < 0.001) and shorter survival (p = 0.036). On MRI, AEs were larger (p = 0.007); had a higher apparent diffusion coefficient value (ADCmin) (p < 0.001), higher ADC ratio (p < 0.001), lower diffusion-weighted imaging ratio (p < 0.001), and greater caudal tumor extension (14.36 ± 8.74 mm vs. 7.90 ± 4.10 mm, p = 0.016) with a higher length/width ratio; and were more prone to encase the brainstem (p < 0.001) and vascular structures (p < 0.001). AEs had more lobulated/ring-like enhancement patterns (14/21 [82.4%]), whereas medulloblastomas appeared more patchy/diffused (27/36 [81.8%]) (p < 0.001). The tumor central vein sign was nearly exclusive to medulloblastomas (p = 0.002). CONCLUSION: Compared with AEs, medulloblastomas with TETFVO show lower ADCmin, less brainstem or vascular encasement, less caudal extensions, and the tumor central vein sign. These distinct features can aid in treatment planning and outcome prediction.