Mark N Rubin, MD
A Japanese roommate of mine back in medical school told me that moyamoya translates better to “miasma” than “puff of smoke,” the latter of which is most typically associated with the characteristic angiographic findings in the setting of proximal cerebral arterial occlusion(s). I suppose that is a more apt phrase physiologically, given the well-documented miasma-like “bad air” issues of moyamoya, including altered oxygen extraction fraction and metabolic consumption of oxygen (CMRO2). A group of Japanese investigators sought to better clarify the effect surgical revascularization with extracranial-to-intracranial (EC-IC) bypass surgery.
The study included 12 children and 30 relatively young (30s to 50s) adults. The underwent sophisticated functional neuroimaging with positron emission tomography (PET) scans that allowed the investigators to assess numerous hemodynamic and physiologic parameters including cerebral blood flow (CBF), oxygen extraction fraction (OEF), cerebral blood volume (CBF), and CMRO2. This study was performed pre- and 3-to-4-months post-EC-IC bypass to assess for any difference the intervention may have made. The main pre-operative finding was that most patients had diminished CBF and CMRO2 with elevated CBV and OEF: a hemodynamic pattern that makes sense in the setting of myriad, structurally unsound, tiny collaterals trying to take the place of major arterial “highways.” In brief, the main post-operative finding was that most of these radiographically-determined hemodynamic parameters were corrected toward normalcy with one major caveat: CMRO2 only improved in the kiddos. This finding led the investigators to speculate that perhaps only a young brain without obvious clinical stroke or silent cerebral ischemia can fully recover metabolic activity (as inferred by CMRO2) toward a normal state after revascularization because it can “hibernate.”
To be sure, CMRO2 is only a single functional parameter and is not a direct surrogate of outcome of any sort, so one should not take from this that adults with moyamoya are “a day late and a dollar short.” In fact, the reported outcome over 10 years of follow-up seems favorable (although lacking in details). The idea that a younger, incompletely developed brain maintains some ischemic resilience and plasticity is interesting and plausible, and needs to be investigated further.