Bifurcations of the arteries of the circle of Willis (CoW; an arterial anastomotic circle providing blood to the brain) are a typical location for unruptured, intracranial aneurysms (UIAs) to develop. UIAs are relatively common, with an estimated prevalence of 3% in the general population. Rupture of an UIA leads to aneurysmal subarachnoid hemorrhage (ASAH), a severe subtype of stroke with significant socio-economic burden. Patients who survive an ASAH often require lifelong rehabilitation or nursing home care1.
Task 1: Circle of Willis classification
Anatomical variation of the arteries of the circle of Willis (CoW) is commonly observed across individuals. Studies report absent, hypoplastic or additional arteries to occur in approximately 70% of the population2. Classification of these anatomical variations is important for clinical practice as incompleteness or asymmetry of the CoW has been associated with an increased risk for intracranial vascular diseases, such as unruptured intracranial aneurysms (UIAs)3 or ischemic stroke4. Specific CoW anatomical variations also occur more often within than between families, suggesting a genetic basis for the CoW configuration5. Genetically-regulated components of imaging marker phenotypes may be identified through genome-wide association studies. The discovery of such components may play an important role in improving risk prediction of UIA development.
their findings in 1985. Both CoW parts (anterior and posterior) are categorized in 10 different classes. An anterior class variant may, for instance, relate to a missing anterior communicating artery or missing A1 segment of an anterior cerebral artery. This classification system has often been used for CoW classification across different studies7, 8.
The purpose of this task is classification of CoW variants on TOF-MRA scans according to Lippert’s classification system. The desired classification output contains two classes per scan: one for the anterior CoW variant and one for the posterior CoW variant.
Task 2: Circle of Willis quantification
Variation in CoW configuration, bifurcation angles and diameters of CoW arteries are one of the few established morphological imaging markers predictive of unruptured, intracranial aneurysm (UIA) development3. Long-term serial screening for UIAs in first-degree family members of ASAH patients is currently recommended with UIAs identified in 11% during first and 8% during follow-up screening9. This shows that the screening process is still suboptimal; in the majority of the screened individuals no UIAs are identified.
New risk factors that can distinguish individuals who are at the highest risk of UIAs would substantially improve the screening process. High-risk individuals could be screened more frequently, whereas the screening frequency for low-risk individuals could be reduced or stopped. Automated assessment of CoW artery diameters and bifurcation angles would facilitate the evaluation of large screening cohorts and benefit the search for new risk factors predictive of UIA development.