Magnetic Resonance Angiographic Evaluation of Circle of Willis in General Population: A Morphologic Study in 507 Cases

The purpose of this study is to evaluate and to describe the prevalence and pattern of circle of Willis (COW) arterial variants seen in non-contrasted three-dimensional time-of-flight MR angiography (3D-TOF-MRA) in a large series of patients. A review of the results of 507 consecutive normal subjects undergoing 3D-TOF- MRA of COW was performed retrospectively. There were 241 males and 266 females, aged from 18 to 89 years. A 1.5-T scanner was used in all these studies. The anatomic variants of anterior and posterior parts of the Circle of Willis were evaluated on maximal intensity projection (MIP) images and the diameters of its major constituents were measured. In these 507 cases, 397 (78.30%) cases have complete anterior parts of the COW; 129 (25.44%) cases have complete posterior parts of the COW and 89 (21.30%) cases demonstrate entire configuration of the Circle. Ten types of variations of anterior and posterior parts of the circle were recognized.