The haemosiderin cap sign refers to an MR imaging feature in some spinal tumourswhere 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 hemangioblastomas and paragangliomasand therefore it is suggestive of but not pathognomonic for ependymoma.