Cerebral Arterial Circle (Circle of Willis)

46 Cerebral Arterial Circle (Circle of Willis)

F. Goetz, A. Giesemann

There are many anomalies of the arteries at the base of the skull.¹^–⁷ Some studies deal with anomalies of the internal carotid artery⁸^–¹³ and others with the circle of Willis¹⁴^–²⁶ or its branches as the middle cerebral artery²⁷^–³⁰ or cerebellar arteries.³¹^,³² For didactic reasons, the anomalies of the anterior area,¹⁹^,³³^–³⁶ posterior area,¹⁹^,³⁷^–³⁹ and the basilar artery⁴⁰ are depicted separately. These anomalies can be combined in different individuals and result in many different types. The frequencies given here are a compromise between radiological and anatomical studies. Vessels were termed “small” or “absent” (e.g., Fig. 46.13) when only negligible collateral circulation took place via such a route.

The recognition of cerebral variants is important as some of these variants might turn pathological in a surgical setting and can influence pathological changes such as brain infarcts and aneurysms.⁷

46.1 Anterior Part of the Cerebral Circle

Fig. 46.1 Circle of Willis. Schematic with indication of arteries.

Fig. 46.2 “Normal” situation (60%). Schematic.

Fig. 46.3 Two anterior communicating arteries (10%).

Fig. 46.4 The median artery of the corpus callosum originates from the anterior communicating artery (10%). Schematic.

Fig. 46.5 Instead of the anterior communicating artery, a lateral anastomosis between the two anterior cerebral arteries is present (3%). Schematic (a) and X-ray angiography, anterior view of the right and left internal carotid artery (b). 1 Anterior communicating artery; 2 anterior cerebral artery; 3 middle cerebral artery; 4 internal carotid artery.

Fig. 46.6 Both anterior cerebral arteries combine partly in a common trunk (5%). Schematic.

Fig. 46.7 Both anterior cerebral arteries originate from one internal carotid artery (10%). Schematic.

Fig. 46.8 Absence of the anterior communicating artery (1%). Schematic.

Fig. 46.9 Accessory middle cerebral artery (1%). Schematic.

Fig. 46.10 Absence of one internal carotid artery; the middle cerebral artery originates from the basilar artery (0.1%). Schematic.

Fig. 46.11 Absence of one internal carotid artery; the middle cerebral artery originates from the other internal carotid artery (0.1%). Schematic.

46.2 Posterior Part of the Cerebral Circle

Fig. 46.12 “Normal situation (55%). Schematic.

Fig. 46.13 The posterior communicating artery is absent or very small on one side (10%). Schematic.

Fig. 46.14 The posterior communicating artery is absent or very small on both sides (<1%). Schematic.

Fig. 46.15 On one side the posterior cerebral artery originates from the internal carotid artery (<1%). Schematic (a) and X-ray angiography, right internal carotid artery injection, lateral view with a dominant posterior communicating artery and anterior view of the left vertebral artery; not hypoplasia of the so-called P1-segment of the right posterior cerebral artery (b). 1 Posterior cerebral artery (P2 segment); 2 vertebral artery; 3 basilar artery; 4 right internal carotid artery; 5 posterior communicating artery.

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