The carotid artery is unique; it is the only vessel to bifurcate into a bulb larger than itself. The history of its anatomic description, understanding of its pathophysiology and evolution of its imaging are relevant to current controversies regarding measurement of stenosis, surgical/endovascular therapies and medical management of carotid stenosis in stroke prevention. Treatment decisions on millions of symptomatic and asymptomatic patients are routinely based on information from clinical trials from over 30 years ago. This article briefly summarizes the highlights of past research in key areas and discuss how they led to current challenges of diagnosis and treatment.

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.

A 62-year-old male presented to hospital with acute aphasia. His past medical history was significant for a previous left middle cerebral artery stroke, from which he fully recovered, hypertension, dyslipidemia, coronary artery disease, one episode of atrial fibrillation postoperatively, and thalidomide exposure in utero. Although initially he was thought to be aphasic, on further examination, he demonstrated significant abulia. His level of consciousness was normal, and neurological examination was otherwise unremarkable. A CT angiogram of the head and neck was performed. The patient was not a candidate for acute therapy, as he had established stroke on imaging, and the time of onset was unclear.

Purpose: We measured anterior cerebral artery (ACA)-middle cerebral artery (MCA) and posterior cerebral artery (PCA)-MCA pial filling on single-phase computed tomography angiograms (sCTAs) in acute ischemic stroke and correlate with the CTA-based Massachusetts General Hospital (MGH) and digital subtraction angiography (DSA)-based American Society of Interventional and Therapeutic Neuroradiology (ASITN) score. Methods: Patients with acute stroke and M1 MCA±intracranial internal carotid artery occlusion on baseline CTA were included. Baseline sCTA was assessed for phase of image acquisition. An evaluator assessed collaterals using the Calgary Collateral (CC) Score (measures pial arterial filling in ACA-MCA and PCA-MCA regions separately), the CTA-based MGH score, and on DSA using the ASITN score. Infarct volumes were measured on 24- to 48-hour magnetic resonance imaging/ computed tomography. Results: Of 106 patients, baseline sCTA was acquired in early arterial phase in 9.9%, peak arterial in 50.7%, equilibrium in 32.4%, early venous in 5.6%, and late venous in 1.4%. Variance in ACA-MCA collaterals explained only 32% of variance in PCA-MCA collaterals on the CC score (Spearman’s correlation coefficient rho [rho]=0.56). Correlation between ACA-MCA collaterals and the MGH score was strong (rho=0.8); correlation between PCA-MCA collaterals and this score was modest (rho=0.54). Correlation between ACA-MCA collaterals and the ASITN score was modest (n=53, rho=0.43); and correlation between PCA-MCA collaterals and ASITN score was poor (rho=0.33). Of the CTA-based scores, the CC Score (Akaike [AIC] 1022) was better at predicting follow-up infarct volumes than was the MGH score (AIC 1029). Conclusion: Collateral assessments in acute ischemic stroke are best done using CTA with temporal resolution and by assessing regional variability. ACA-MCA and MCA-PCA collaterals should be evaluated separately.

Background: Computed tomography perfusion (CTP) is increasingly being used in the setting of acute ischemic stroke (AIS). The aim of the current study was to compare the prognostic utility of, and inter-observer variation between, baseline appearances on non-contrast CT (using Alberta Stroke Program Early CT score(ASPECTS)) and on CTP for predicting final infarct volume. We also assessed impact of training on interpretation of these images. Methods: Retrospectively, plain head computed tomography (CT) and CTP images at presentation and CT or diffusion imaging on follow up of patients with AIS were analyzed. The lesion volume on different CTP parameters was then correlated with the final infarct volume. This analysis was done by a Neuroradiologist, a stroke Neurologist and a medical student. Kappa statistics and Intra-class correlation coefficients were used for agreement between readers. Pearson correlation coefficients were used.Results: Thirty eight patients with AIS met all inclusion criteria. There was very good agreement among all readers for the CTP parameters. There was only fair agreement for ASPECT score. Correlation coefficient (r-square) between CTP parameters and final infarct volume showed that cerebral blood volume was the best parameter to predict the final infarct volume followed by cerebral blood flow and time to peak. The best reader to predict the final infarct volume on the initial CT perfusion study was the neuroradiologist followed by medical student and stroke neurologist. Conclusions: Cerebral blood volume defect correlated the best with the final infarct volume. There was a very good inter-observer agreement for all the CTP maps in predicting the final infarct volume despite the wide variation in the experience of the readers.