Kristen Yeom

We knew arterial spin-labeling (ASL) perfusion would be great for stroke, but we were even more excited to get it rolled out for kids. It was a match made in heaven—no IV pricks, no power injector, no veins bursting, and heck, no gadolinium—and this was before we even knew this thing sticks in the brain. High labeling efficiency and SNR in kids were bonus items. So on April 13, 2010, we added ASL to our brain tumor protocol. Brain tumors occur at all ages, from babies to teens, and sadly, are the most common solid cancers in kids. They also come in all shapes and sizes and sometimes bring bizarre cells of origin from an embryonic era, just to baffle us radiologists. We had T2, DWI, and SWI, but maybe 1 more in our alphabet soup might have brought out a physiologic tumor ingredient.

Each time a new tumor case popped up, we all ogled ASL perfusion. “What did it show?” “I dunno, but it looks funny.” Our neurosurgeons were curious, too. “Did that tumor come back? What did the ASL show?”

“Is it supposed to be bright like that?” With so many tumor types, ranging from glioblastoma to ganglioneuroblastoma, and more intra-axial than extra-axial meningiomas, we had even more questions. So sometime around 2012, we rounded up all our pediatric brain tumors and probed tumor ASL. We segmented the tumors, crunched the numbers, and swirled ideas, thinking we might sort out the bad from the less bad, and conquer the world while we were at it. No such luck. The tumor perfusion metrics were all over the place; pilocytics might just as well have been as bright or dark as the glioblastomas. The project was another dud like many before. We buried it in my desk. RIP.

Months later, Lex Mitchell, our bright neuroradiology fellow, decided to dig through my cold case files and stumbled upon our tumor ASL project. “Can I take a look at this?” “Sure, Lex, but just to warn you, it was a flop before.” But we got wiser. We crunched the numbers again, but this time, we obtained relative maximal tumor perfusion, normalized to contralateral brain. After this extra step, all the tumors neatly fell into their pathologic classifications, except for medulloblastomas. We were excited to see this and added more tumors in our final work.

Here, we present perfusion patterns reflective of pediatric brain tumor pathologies. Based on our work, we now query tumors that look pilocytic but with very high ASL signals are something different, more aggressive or high-grade. We have also uncovered tiny, postirradiation meningiomas sitting in the skull base foramina that may have gone unrecognized. Although obvious in hindsight, a key to this study was to assess tumor perfusion relative to the individual brain in order to account for age- and other patient-dependent variations of cerebral perfusion. For example, we also learned that cerebral perfusion is altered in children acutely presenting with hydrocephalus, a topic we explore in another AJNR article.   We hope the readers find ASL signal useful in their encounters with pediatric brain tumors as we have.

Read this article at AJNR.org …