Rare Transsellar Collateral Artery and Secondary Ophthalmic Artery Aneurysm in a Young Adult with Internal Carotid Artery Aplasia

Internal carotid artery (ICA) aplasia is a rare congenital abnormality in which the third aortic arch fails to develop. Most collateral circulation will originate from the circle of Willis, with other sites being rare. Changes in flow through the collateral vasculature result in aneurysm formation at a young age. A 38-year-old woman had an incidental diagnosis of left ICA aplasia and right ophthalmic artery aneurysm. Arteriography demonstrated that the left supraclinoid ICA originated from the right cavernous ICA and appeared as an anomalous hyper-trophied transsellar artery on angiography. Her flow-related aneurysm was treated uneventfully. The present case demonstrates an extremely rare Lie type D collateralization pattern and secondary flow-rated aneurysm in the context of ICA aplasia. Patients identified with this anatomic variant should be monitored for subsequent aneurysm formation. Identification of this variant before endo-vascular and transsphenoidal procedures is crucial to prevent major intracranial vessel injury.