How often is haemosiderin not visible on routine MRI following traumatic intracerebral haemorrhage?

Intracerebral haemorrhage may be visible indefinitely on MRI, due to persis tence of haemosiderin in macrophages around the lesion, but it is not clear whether all haemorrhages produce haemosiderin or, if not, what proportion cannot be identified as former haemorrhages on routine MRI. We performed ro utine MRI (spin-echo T2- and proton-density weighted images) in 116 survivo rs of moderate to severe head injury, 1-5 years after injury. We reviewed t he images blindly and correlated them with CT in the acute stage, to determ ine how many haemorrhages from the acute stage were identifiable by virtue of haemosiderin deposition on late MRI. Of 106 haemorrhages in 78 patients on CT at the time of injury, 96 (90 %) were visible as haemosiderin on late MRI. Of the old haemorrhages without haemosiderin, seven of ten were in pa tients where another haemorrhage with haemosiderin was still visible elsewh ere in the brain. No patient or haemorrhage features explained the formatio n or absence of haemosiderin. Thus about 10 % of definite haematomas show n o trace of haemosiderin on routine spin-echo MRI. Radiologists should be al erted to supplement routine spin-echo with gradient-echo sequences if there is a reason to suspect, or specifically exclude, prior haemorrhage.