Rare Segmental Agenesis of Internal Carotid Artery without Rete-Like Collaterals: A Case Report.

Objective: Internal carotid artery (ICA) agenesis has been classified into six types: A-F. Type F demonstrates distal reconstitution of the ICA via anastomosis with distal branches of the external carotid artery. Herein, we report the ICA agenesis of type F without rete-like collaterals, which has not been previously reported.

Case presentation: An 80-year-old woman presented with segmental agenesis of the right ICA accompanied by an unruptured intracranial aneurysm. Stent-assisted coil embolization was successfully performed. Digital subtraction angiography showed segmental agenesis of the right ICA from the cervical to the ascending foramen lacerum segment, which was preoperatively supplied with collateral blood flow by a dilated right accessory meningeal artery (AMA) anastomosed with the inferolateral trunk (ILT)-posteromedial branch. Based on the segmental concept, the case was diagnosed with segment 7 (horizontal intracavernous portion until ICA branches off the ILT) agenesis, which may have resulted in secondary regression of the ICA proximal to segment 7. According to the ICA agenesis classification, this was of type F because the case showed collateral flow to the distal ICA via transcranial anastomoses from the AMA without carotid rete-like collaterals.

Conclusion: These findings suggest that the carotid rete-like collaterals did not form because the AMA was first developed during embryonic development.