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Background
Vascular pathology may be the primary reason for an incidental finding on contrast-enhanced imaging examination. The goal of this presentation is to provide a broad overview of the range of neurovascular findings one may encounter, from benign congenital variations to neoplasms.

Educational Goals / Teaching Points
1. Congenital/anatomic variants, including aortic arch and major branches, Circle of Willis, and persistent carotid-vertebrobasilar anastomoses, arterial fenestration, and junctional dilatation of the basilar artery tip. 2. Review International Society for the Study of Vascular Anomalies characterization of vascular anomalies, primarily discerning vascular malformations from tumors with case examples. Tips will be provided to help discern vascular lesions from similar appearing processes in the head and neck region. 3. Examine other vascular disorders including Moyamoya disease, fibromuscular dysplasia (including carotid intimal variant), reversible cerebral vasoconstriction syndrome, and amyloid angiopathy.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Infantile hemangiomas and congenital hemangiomas are vascular neoplasms of infancy that are similar in their early presentation and imaging characteristics. Both appear as enhancing masses with feeding and draining vessels. Infantile hemangiomas have rapid early proliferation, whereas congenital hemangiomas have variable types of involution. Vascular malformations are a broad category of structural lesions that are caused by errors in embryonic vascular morphogenesis and often grow slowly and proportionately with the patient. They are classified as simple versus combined depending on the vessel types involved and whether or not there is an arterial component involved (high-flow vs low-flow). These include arteriovenous malformations, capillary malformations, lymphatic malformations, and venous malformations. These entities are also associated with specific genetic associations. Moyamoya angiopathy is a progressive steno-occlusive process involving the terminal internal carotid arteries with subsequent development of abnormal collateral vessels that create a "puff of smoke" appearance on conventional angiogram. There are many forms of vascular anatomic variants that involve the Circle of Willis and carotid-vertebrobasilar system. For example, the persistent trigeminal artery is a type of carotid-basilar anastomosis that is found in 0.1–1% of angiograms and is classified typically using the Saltzman classification. This artery is usually found communicating the distal internal carotid artery and the vertebrobasilar arteries or its branches.

Conclusion
Vascular pathology is a broad topic consisting of congenital anomalies, malformations, neoplasms, and other forms of angiopathies that can be difficult to differentiate. Despite this, these entities all have distinct clinical and imaging characteristics that can be used to differentiate them.