Cerebral intraparenchymal hyperattenuation post thrombolysis

Cerebral intraparenchymal hyperattenuations have been increasingly recognised on CT scans following mechanical thrombectomy for treatment of thromboembolic ischaemic stroke. It is a term that encompasses both contrast staining and petechial haemorrhagic change, and is used as distinguishing between the two is not always easy. 

The distribution of cerebral intraparenchymal hyperattenuation correlates with the eventual volume of infarction – in other words, the pre-procedural infarct core plus any portions of penumbra which despite treatment will go on to infarct ¹. 

As such, intraparenchymal hyperattenuations immediately following mechanical thrombectomy, observed either on conventional multidetectormulti-detector CT or flat-panel CT, can provide prognostic information as to the eventual volume of infarction ¹. 

Radiographic features

Distinguishing between contrast staining and petechial haemorrhagic transformation is not easy, particularly when obtained on current flat-panel CT (obtained in the cath-lab). 

Contrast staining

Contrast staining typically appears as areas of hyperdensity mostly confined to grey matter (cortex and deep grey matter) and represent areas of blood-brain barrier breakdown secondary to ischaemia with microvascular extravasation of contrast into the extracellular space ¹. Typically such staining clears within the first 19-24 hours after the procedure ². 

Dual-energy CT is also able to distinguish hyperdensity due to contrast versus hyperdensity due to haemorrhage ³. 

Petechial haemorrhagic transformation

Petechial haemorrhagic transformation of an ischaemic infarct (as opposed to macroscopic solid cerebral haemorrhages also sometimes encountered) can have a very similar appearance. Follow-up CT performed at least 19-24 hours following intervention is the most specific way to differentiate, with persistent hyperdensity consistent with haemorrhage whereas contrast staining will reduce in density over time ².