On CT prior to contrast administration, the tumour is predominantly isodense midline posterior fossa mass with variable enhancement. Cyst formation is common and readily visible on CT. Calcifications appear in 44% of cases, and are either diffuse or coarsely nodular.
MRI signal intensity is unable to distinguish ependymoma form other intracranial gliomas, but MRI does define the location and gross morphology of the tumour. The ability to accurately define the caudal extent of the tumour has an important impact on radiation treatment planning.
Ependymomas appear hypointense on T1-weighted images, hyperintense on T2-weighted images, and enhance with gadolinium. Ependymomas present as a nonspecific heterogenous signal. This heterogeneity in imaging studies can reflect cystic regions, areas of necrosis, hemorrhage, and calcification. Contrast enhancement occurs in nearly all ependymomas. While CT and MRI are able to give a presumptive diagnosis of tumour type, a final diagnosis cannot be made without tissue sampling.
Table 6. Differential use of CT and MRI in ependymoma imaging.
| |
CT |
MRI |
| Role |
Initial evaluation for intracranial hemorrhage or mass |
Better characterizes the tumour. Findings lead to a presumptive diagnosis |
| Appearance |
Higher tumour density relative to brain. Calcification (50% of cases)
Heterogeneous enhancement (2/3 of cases) |
Nonspecific heterogeneous signal. T1 images are hypointense T2 images enhance with gadolinium |
Image #1 T1 weighted MRI of an ependymoma. Tumour is hypointense and not well visualized.
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Image #2 T2 weighted MRI of an ependymoma. The tumour is hyperintense
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