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High resolution MR angiography of the posterior cerebral circulation: variants, incidence and clinical impact

Objective: In the embryonic period, several developmental anomalies of the posterior cerebral circulation might occur. Digital subtractive angiography used to be the imaging technique of choice for the illustration of such variations. Nowadays, the development of MR imaging has led to a new entry in the diagnostic archer’s quivery, the MR an- giography, with which most of these variations may be diagnosed. Purpose of this study is to illustrate these anatomic variants, their incidence and their potential clinical significance. Materials and Methods: We retrospectively reviewed 282 MR angiographies performed in our institution, in order to assess the posterior cerebral circulation. The imaging findings (including both normal development and variations) were depicted. Results: In our study 61/282 (21.63%) MR angiographies were positive for imaging findings concerning variations of the vertebrobasilar system. These variations included abnormal origin of the vertebral artery (0.7%), unilateral aplasia or hypoplasia (8.86%), unilateral aplasia or hypoplasia of the distal part of the vertebral artery (3.85%), and unilateral or bilateral fetal posterior cerebral artery (7.7%). These results show that anatomic variations of the posterior cerebral circulation are not very uncommon in the population. Conclusion: High resolution Magnetic Resonance Angiography provides excellent interpretation of the vertebral arteries, allowing depiction of all anatomic variations. Knowing these anatomic variations is important, espe- cially for clinicians and patients planning a surgical operation or an interventional radiology technique. Furthermore, it contributes to avoiding potential diagnostic pitfalls or to explaining unusual acute vascular cerebral events.