The haemosiderin cap sign refers to an MR imaging feature in some spinal tumours where a cap of T2 hypointense haemosiderin is above and/or below the tumour due to previous haemorrhage.
It is most often associated with spinal cord ependymomas, being seen in 20-33% of these cases 1. The sign, however, may also be seen in haemangioblastomas and paragangliomas and therefore it is suggestive of but not pathognomonic for ependymoma.
In addition, larger cavernous malformations of the spine may appear to lack a complete haemosiderin ring where they reach the pial surface, and thus develop a haemosiderin 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