In Re: Reversible Ischemia Determined by Xenon-Enhanced CT after 90 Minutes of Complete Basilar Artery Occlusion

In their case report, Reversible ischemia determined by xenon-enhanced CT after 90 minutes of complete basilar artery occlusion, Levy et al describe a patient with acute basilar artery occlusion whose right occipital lobe remained viable after reperfusion, despite 90 minutes with blood flow to this region reduced to 6 mL /100 g per minute (1). This finding—the rationale for their report—suggests a lower threshold for reversible ischemia at 90 minutes (at least in the posterior circulation) than the 10–12 mL /100 g per minute that is generally accepted.

The basis for their diagnosis of reversible ischemia, however, is the finding of resolution of hypoattenuation in the medial right occipital lobe on a CT scan done 12 days after stroke, as compared with a scan obtained 2 days after stroke. The authors do not provide a late CT scan (2 to 3 months after ictus), an MR scan, or an autopsy report that documents that cavitation has not subsequently evolved. Such documentation is necessary to prove that the normal attenuation coefficients found at 12 days were because of preservation of normal tissue rather than the result of a more likely phenomenon—fogging of an evolving infarction (2–4).

Infarct fogging, the apparent normalization of the CT scan hypodensity associated with an acute stroke, typically occurs between the second and third weeks after infarction. It is believed to be caused by the capillary proliferation and macrophage invasion into infarcted brain parenchyma that occurs after the resolution of acute edema but before the development of tissue cavitation.