Given the T1 and T2 characteristics of the intracranial haemorrhages, what blood product is present?
Extracellular methaemoglobin (high on both T1 and T2).
What is the approximate time since the initial injury?
Methaemoglobin is the "late subacute" blood product, seen at 7-14 to 28 days. In this case, the MRI was performed 2 weeks following trauma.
What MRI features suggest that the right frontotemporal ring enhancing lesions are haematomas, rather than abscesses?
Central high T1 signal (low T1 in abscess), mild restricted diffusion, not clearly conforming to the central area within the enhancing rim, relatively mild associated oedema.
There are multiple findings which may be correlated with the earlier CTs:
- The ring enhancing right frontotemporal lesions seen on the second CT are present as areas of T2 and T1 hyperintensity with associated peripheral enhancement. There is some increased DWI signal, although not conforming clearly to the areas surrounded by ring enhancement. The associated oedema is quite mild.
- The foci of T2 and T1 hyperintensity within the right dorsolateral midbrain and left thalamus correspond to the areas of haemorrhage seen on the initial CT.
- There is T2 hyperintensity and some associated enhancement within the lateral aspect of the left cerebellar hemisphere (as seen on the second CT).
- Thin subdural haematoma overlies the right cerebral hemisphere. There is linear low T2* signal compatible with haemosiderin.
- Increased DWI signal is present within the posterior body and splenium of the corpus callosum as well as the left cerebral peduncle and posterior left thalamus.
- The MRI appearance of the right frontal and temporal "ring enhancing lesions" favours subacute haemorrhagic contusions.
- As expected from the CTs, the MRI shows the appearance of severe diffuse axonal injury (grade 3).