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.
- 1. Koeller KK, Rosenblum RS, Morrison AL. Neoplasms of the spinal cord and filum terminale: radiologic-pathologic correlation. Radiographics. 20 (6): 1721-49. Radiographics (citation) - Pubmed citation
- 2. Haaga JR, Boll D. CT and MRI of the whole body. Mosby. (2009) ISBN:0323053750. Read it at Google Books - Find it at Amazon