A 56-year-old woman with
Down syndrome presented with right-sided weakness and
dysarthria, and was found on CT/CTA to have a left middle cerebral artery
infarct secondary to
moyamoya disease. Her left posterior inferior cerebellar artery (
PICA) was fed both by the left vertebral artery, and the left ascending pharyngeal artery (APA), with a variant origin from the internal carotid artery (ICA), then passing through the jugular foramen (Figure 1). Her right
PICA originated exclusively from her right occipital artery, also via the jugular foramen (Figure 2). The left vertebral artery originated directly from the aortic arch, whereas the right vertebral artery originated from the brachiocephalic trunk. In addition, she had a trifurcated anterior cerebral artery (ACA), and just prior to this trifurcation, her left ACA was partially supplied by the left ICA, via a superior hypophyseal artery. This case is noteworthy for several reasons. First, though it is exceedingly rare to have the
PICA supplied by the jugular branch of the APA, this is the first reported case with an ICA origin of that APA.1,2 The fact that both PICAs in this patient originate from the anterior circulation should remind clinicians that in unexplained posterior circulation
infarctions, vascular anatomy should be explored, as carotid-vertebrobasilar anastomoses such as these are rare, but possible. Lastly, the conjunction of
moyamoya disease and anomalies of the vertebrobasilar system in a patient with
Down syndrome raises interesting questions about the influence of
trisomy 21 on the developing vasculature. Connections from the APA to the vertebrobasilar system are hypothesized to result from a lack of regression of an embryological anastomosis, in line with the more common persistent trigeminal and persistent hypoglossal arteries.1 Patients with
moyamoya disease have a significantly higher rate of persistent carotid-vertebrobasilar anastomoses than the general population,3 and are also 26 times more likely to have
Down syndrome.4 Correspondingly, patients with
Down syndrome have significantly higher levels of
moyamoya disease, and are more than 10 times as likely as the general population to have abnormalities of the Circle of Willis5 and vertebral arteries.6 Several genes on chromosome 21 are known to affect angiogenesis, namely
collagen XIII/
endostatin (COL18A1), DYRK1A, and
Down syndrome candidate region 1 (DSCR1), possibly through inhibition of
VEGF activity.7 Whether additional copies of these genes are responsible for the anomalous vascular development seen in
Down syndrome, in turn predisposing to the development of
moyamoya disease, could benefit from further exploration.