后颅窝室管膜瘤A组（EPN_PFA）和B组（EPN_PFB）通过DNA甲基化可予以区分，并具有不同的预后。我们比较了EPN_PFA和EPN_PFB在首次检查时的磁共振成像特征。我们对两个中心的68例后颅窝室管膜瘤患者的术前影像进行了三位独立评估者的回顾性研究，评估者对组织分子分组没有进行知情。我们比较了两组之间的病变位置、瘤体扩展程度、瘤体体积、脑积水、钙化、组织成分、增强或扩散信号以及组织病理学数据（细胞密度、钙化、坏死、有丝分裂、血管化和微血管增殖）。使用Fisher精确检验对分类数据进行组间比较，使用Mann-Whitney检验对定量数据进行比较。我们使用Benjamini-Hochberg法对p值进行修正，以纠正多重检验的影响。总共有56例患者被归类为EPN_PFA，12例被归类为EPN_PFB，分别具有中位年龄2岁和20岁（p = 0.0008）。EPN_PFA瘤体体积中位数较大（57 vs 29 cm3，p = 0.003），伴有更明显的脑积水（p = 0.002）。61%的EPN_PFA患者瘤体定位于第四脑室的中央位置，而92%的EPN_PFB患者在此位置（p = 0.01）。93%的EPN_PFA患者有肿瘤内钙化，而40%的EPN_PFB患者有肿瘤内钙化（p = 0.001）。EPN_PFA主要侵犯后颅洞孔，尤其是Luschka小孔（p = 0.0008）。EPN_PFA瘤体显示5%为完整均质增强，而EPN_PFB瘤体75%显示完整均质增强（p = 0.0008）。所有主要囊性肿瘤为EPN_PFB（p = 0.002）。EPN_PFA的最小和最大相对扩散系数（ADC）略低（p = 0.02和p = 0.01）。影像学的形态特征在区分后颅窝室管膜瘤亚型上有所不同，可能有助于术前鉴别。本研究提供了一种区分A组和B组室管膜瘤的工具，最终将有助于在患者管理早期阶段调整治疗策略。 • 后颅窝室管膜瘤亚型通常具有不同的影像学特征。 • 后颅窝室管膜瘤A组通常为中线或侧向组织钙化肿块，增强不完全，多见于儿童，常导致明显的脑积水和后颅窝孔的侵犯。 • 后颅窝室管膜瘤B组通常为中线非钙化肿块，多见于青少年和成年人，以囊性为主，侵入性小，整体均质增强。 © 2023. European Society of Radiology 独家授权，作者所。

Posterior fossa ependymoma group A (EPN_PFA) and group B (EPN_PFB) can be distinguished by their DNA methylation and give rise to different prognoses. We compared the MRI characteristics of EPN_PFA and EPN_PFB at presentation.Preoperative imaging of 68 patients with posterior fossa ependymoma from two centers was reviewed by three independent readers, blinded for histomolecular grouping. Location, tumor extension, tumor volume, hydrocephalus, calcifications, tissue component, enhancement or diffusion signal, and histopathological data (cellular density, calcifications, necrosis, mitoses, vascularization, and microvascular proliferation) were compared between the groups. Categorical data were compared between groups using Fisher's exact tests, and quantitative data using Mann-Whitney tests. We performed a Benjamini-Hochberg correction of the p values to account for multiple tests.Fifty-six patients were categorized as EPN_PFA and 12 as EPN_PFB, with median ages of 2 and 20 years, respectively (p = 0.0008). The median EPN_PFA tumoral volume was larger (57 vs 29 cm3, p = 0.003), with more pronounced hydrocephalus (p = 0.002). EPN_PFA showed an exclusive central position within the 4th ventricle in 61% of patients vs 92% for EPN_PFB (p = 0.01). Intratumor calcifications were found in 93% of EPN_PFA vs 40% of EPN_PFB (p = 0.001). Invasion of the posterior fossa foramina was mostly found for EPN_PFA, particularly the foramina of Luschka (p = 0.0008). EPN_PFA showed whole and homogeneous tumor enhancement in 5% vs 75% of EPN_PFB (p = 0.0008). All mainly cystic tumors were EPN_PFB (p = 0.002). The minimal and maximal relative ADC was slightly lower in EPN_PFA (p = 0.02 and p = 0.01, respectively).Morphological characteristics from imaging differ between posterior fossa ependymoma subtypes and may help to distinguish them preoperatively.This study provides a tool to differentiate between group A and group B ependymomas, which will ultimately allow the therapeutic strategy to be adapted in the early stages of patient management.• Posterior fossa ependymoma subtypes often have different imaging characteristics. • Posterior fossa ependymomas group A are commonly median or lateral tissular calcified masses, with incomplete enhancement, affecting young children and responsible for pronounced hydrocephalus and invasion of the posterior fossa foramina. • Posterior fossa ependymomas group B are commonly median non-calcified masses of adolescents and adults, predominantly cystic, and minimally invasive, with total and homogeneous enhancement.© 2023. The Author(s), under exclusive licence to European Society of Radiology.