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Graph demonstrating the evolution of the density on CT of intracranial haemorrhage such as a subdural haematoma.
A few important facts should be appreciated.
- hyperacute haematoma (prior to clotting) will be the same density of unclotted blood - it is made up of the same stuff after all. This will vary according to haematocrit but will usually be less than 60HU (something like 35-45HU).
- haematoma increases in density as it clots by contracting solid components and expelling plasma, thus emboli that are "prepared earlier" are immediately hyperdense (e.g. dense artery sign) whereas in situ thrombosis may take a little time to become obvious.
- over days to a few weeks, the blood will become isodense to brain and may be difficult to identify (e.g. isodense subdural)
- eventually, the density will be similar to CSF and may mimic a subdural hygroma
Most importantly, the time it takes for these changes to occur is variable depending on the location and size of the haematoma and numerous host factors.
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This is an old old old diagram I made years ago and does not show the initial increase in density. I have kept it here for historical reasons only. I'm sentimental that way.
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