Introduction: Distinct origins of the external carotid artery (ECA) and the internal carotid artery (ICA) from the aortic arch have been rarely described and represent an aberrant development of the aortic arches during fetal life. This anatomical variation is usually discovered incidentally; infrequently, an aneurysm of the cervical ICA might accompany this rare configuration. The authors describe one such case in a patient with Noonan Syndrome who presented with pulsatile neck mass.

Methods: Diagnostic features and management of the aneurysm and a review of the literature are presented.

Results: A literature review of separate origins of the ICA and ECA from the aortic arch revealed few sporadic case reports. Associated vascular anomalies such as persistent trigeminal artery, persistent proatlantal artery, cervical aortic arch, double aortic arches have been described (1, 2). Our case demonstrates absence of the CCA with agenesis of the carotid bulb from regression of the 3rd aortic arch with separate origins of the ECA and ICA from the arch. The ICA below the aneurysm has a redundant dysplastic appearance. We postulate that the dorsal end of the 3rd aortic arch on the left side failed to regress completely which subsequently led to the aneurysm formation of the ICA. Our hypothesis is based on the location of the aneurysm, at the level of C3 vertebra, which is one of the more common positions of the carotid bulb (3), interposed between the ICA and ECA. Interestingly, on imaging and intra-operatively, separate entry and exit openings of the ICA were noted inside the aneurysm, which also supports our hypothesis.

Conclusions: We present a very rare anatomic variant of aortic arch and its branches in a patient with Noonan Syndrome along with a large cervical ICA aneurysm leading to dysphagia. Given the overall anatomy of carotid arteries and location of the aneurysm, we believe that incomplete regression of the third fetal aortic arch, which normally persists to form the carotid bulb, is the underlying process that resulted in distal ICA aneurysm formation.

Patient Care: Presentation of an extremely rare clinical case report that pertains to our cerebrovascular field with treatment and follow through.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the embryological development process of the vessels feeding the cerebral circulation, 2) Developmental anomalies involved in the development of the carotids and vertebral arteries, 3) discuss in small groups the pathology associated with such anomalous vessels and how they can clinically present, and 4) identify an effective treatment paradigm tailored to the patient's clinical condition and presentation.

References: 1. Lie TA. Congenital anomalies of the carotid arteries: An angiographic study and a review of the literature. Amsterdam: ExcerptaMedica Foundation; 1968:30–35. 2. Koçogullari CU, Becit N, Erkut B, Koçak H. A Case Report of an Abnormal Configuration of the Branches of Aortic Arch with an Internal Carotid Artery Aneurysm. EJVES Extra. 2005 Mar 31;9(3):44-5. 3. Kurkcuoglu A, Aytekin C, Oktem H, Pelin C. Morphological variation of carotid artery bifurcation level in digital angiography. Folia Morphol (Warsz). 2015;74(2):206-11.