MRI has supplanted CT scanning as the diagnostic modality of choice in the workup and follow-up observation of intracranial neoplasms, including ependymoma. The most appropriate role for MRI in the treatment of ependymoma is in the detection of tumor and direction of its resection and/or irradiation. MRI is used to monitor ongoing treatment and to survey for recurrence.
Solid portions of ependymoma typically are isointense to hypointense relative to white matter on short recovery time/echo time (TR/TE) T1-weighted images. The tumor is hyperintense to white matter on long TR/TE T2-weighted images. As many as 50% of ependymomas demonstrate signal heterogeneity, which may indicate calcification, necrosis, methemoglobin, hemosiderin, or tumor vascularity. Hypointense foci on both T1- and T2-weighted images suggest hemosiderin, calcium, or necrosis. Cystic changes result in high signal intensity on T2-weighted MRIs.
Signal heterogeneity is a feature useful in distinguishing ependymoma from the more homogeneous medulloblastoma. Calcification and hemorrhagic foci are more typical of ependymoma than medulloblastoma.
Additionally, ependymomas are more apt to extend through the foramina of Luschka and Magendie, hence the term plastic ependymoma. Similarly, choroid plexus papilloma is more homogeneous than ependymoma and lacks the typical irregular margins and surrounding edema of ependymoma.
Enhancement with gadolinium is useful in differentiating tumor from adjacent vasogenic edema and normal brain parenchyma. Without intravenous contrast enhancement, T2-weighted images are more reliable in differentiating tumor margins than are T1-weighted images.
Case credit: Dr Abhijit Datir.