Early DWI reversal in ischaemic stroke (also referred to as diffusion lesion reversal) is sometimes encountered early in the course of ischaemic stroke.

Hyperintensity on DWI develops within minutes of ischaemia and was believed to be highly sensitive and specific in defining the ischaemic core. Over time, however, a number of exceptions to this rule have been described and DWI reversal is one such example.

Terminology

DWI reversal generally refers to the resolution of some or all hyperintensity seen on initial imaging when this is compared to subsequent MRI. Which sequences are used for this later comparison, as well as precise definitions of what is meant by DWI reversal, is variable, resulting in heterogenous incidence and outcomes ^4,6.

Generally, the initial DWI findings are compared to either subsequent DWI studies (so-called DWI-based studies), or FLAIR/T2 (so-called FLAIR/T2-based studies).

Depending on which sequence is used, the incidence of DWI reversal varies:

• DWI-based studies: 26.5% ⁵

• FLAIR/T2-based studies: 6% ⁵

These figures are, however, for partial reversal. Complete reversal is rare, occurring only in 0.8% of cases acute ischaemic stroke ^4,5.

Note: Early DWI reversal should not be confused with ADC pseudonormalisation, which occurs later in the evolution of ischaemic stroke. 

Treatment and prognosis

DWI reversal is most frequently encountered in the setting of reperfusion (endovascular clot retrieval of thrombolysis) within 3 to 6 hours of onset ^1,5.

Overall presence of DWI reversal is associated with some improvement in clinical outcomes (e.g. NIHSS and modified Rankin Scale) ^4,5 although in some/many cases, it is transient, and the abnormal DWI signal returns ^1,2. 

Differential diagnosis

A similar appearance is encountered in other clinical contexts (e.g. hemiplegic migraine, seizure, transient ischaemic attack, transient global amnesia, and in some instances of PRES - those that show a degree of restricted diffusion (26% of cases)), wherein DWI changes resolve ³.