ADC pseudonormalisation is a normal phase encountered in the subacute stage of ischaemic stroke and represents an apparent return to normal healthy brain values on ADC maps which does not, however, represent true resolution of ischaemic damage.
ADC pseudonormalisation is seen typically around 1 week following ischaemic stroke and is thought to be due to a combination of cell wall breakdown and increase of extracellular oedema (both of which result in facilitated diffusion - increased ADC values) 2. At some point, these processes, combined with residual true abnormal restricted diffusion due to cellular swelling, result in ADC values ostensibly returning to those of a normal, healthy brain.
It is important to realise that at the point that ADC values normalise, DWI images (e.g. b = 1000 s/mm2) will continue to show increased signal due to T2 shine-through. It is only later (around 10-15 days) that DWI pseudonormalisation occurs, when ADC values are higher than normal, offsetting the gradually waning T2 signal.
Note: ADC pseudonormalisation should not be confused with early DWI reversal (a.k.a. diffusion lesion reversal), which is seen early in the course of ischaemic infarction, particularly in the setting of reperfusion therapy. Nor should it be confused with T2 washout seen a little later.
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