Hemosiderin cap sign

Last revised by Dimitrios Toumpanakis on 28 Jun 2023

The hemosiderin cap sign refers to an MR imaging feature in some spinal tumors where a cap of T2 hypointense hemosiderin is above and/or below the tumor due to previous hemorrhage. 

It is most often associated with spinal cord ependymomas (20-33% of cases) 1. It may also be seen in hemangioblastomas and paragangliomas and therefore it is suggestive  but not pathognomonic of ependymoma

In addition, larger cavernous malformations of the spine may appear to lack a complete hemosiderin ring where they reach the pial surface, and thus develop a hemosiderin cap. 

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