Anatomic Neuroimaging Characteristics of Posterior Fossa Type A Ependymoma Subgroups

PFA ependymoma types based on location. Sagittal T1- (A) and axial T2-weighted images (B): Midfloor-type posterior fossa ependymomas fill the obex (arrowhead), and a gap may be seen between the roof of the fourth ventricle and the tumor (arrows, A). The brainstem is displaced anteriorly (arrow, B), and in the sagittal plane, it is seen in its entirety in a single sagittal image. Sagittal T1- (C) and axial T2-weighted images (D): Lateral-type posterior fossa ependymomas are centered in the lateral recess of the fourth ventricle or cerebellopontine angle (arrows, C) and displace the brainstem laterally (arrow, D). The brainstem usually cannot be seen in a single sagittal image. Postgadolinium sagittal T1- (E) and axial T2-weighted images (F): Roof-type posterior fossa ependymomas appear closely associated with the roof of the fourth ventricle (arrows, E and F) and do not fill the obex (arrowhead, E). A gap is usually seen between the tumor and the floor of the fourth ventricle (arrowhead, F).