Congenital absence of bilateral ICA: an unusual incidental finding in an adult male

A 55-year-old man presented with headache of 4 weeks duration. There was no history of seizures or vomiting. An MRI of the brain was performed, which revealed no evidence of intracranial space occupying lesion. However, absence of expected flow voids along the course of the petrous and cavernous segments of the intracranial internal carotid arteries (ICA) was noted (figure 1). The sulcal spaces appeared normal with no T2/fluid-attenuated inversion recovery hyperintensities (figure 2). There were no signs of chronic ischaemic changes in the neuroparenchyma (figure 2). Intracranial MR angiogram was subsequently performed, which revealed non-visualisation of bilateral ICAs, prominent bilateral vertebral arteries, and prominent basilar and posterior communicating arteries (figure 3). The PCOMs were supplying both middle cerebral arteries and the anterior cerebral arteries (ACA) via the circle of Willis. The A1 segment of the right ACA was absent with the A2 segment being reformed via the anterior communicating artery (figure 3). There was no evidence of ‘rete’ type collaterals in the intracranial circulation. A CT angiogram (extracranial and intracranial) revealed narrow calibre of both common carotid arteries, with normal external carotid arteries and non-visualisation of the intracranial ICA on both sides (figure 3). The cervical segment of the right ICA was completely absent, while a short …