To describe the first reported case of genetically proven Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) in a patient with bilateral internal carotid artery (ICA) agenesis.

CADASIL (a result of various mutations in the NOTCH 3 gene) is a recognised cause of stroke in the young. Bilateral ICA agenesis is a rare congenital malformation, with few previous reported cases in the literature. CADASIL is not reported to be associated with carotid agenesis.

A 41 year old man initially presented with recurrent orthostatic symptoms associated with increasingly frequent falls. CT angiography revealed absent bilateral ICAs with an ectatic vertebrobasilar arterial tree supplying the intracranial circulation. Skull base CT demonstrated simultaneous absence of the ICAs and bilateral carotid canals, confirming agenesis of bilateral ICAs. MRI of the brain revealed extensive areas of confluent high T2 signal intensity in the subcortical and periventricular zones of both hemispheres.

The patient subsequently developed episodic and progressive headache, dysarthria, ataxia, cognitive impairment and personality changes. Serial MRIs demonstrated radiological progression of cerebral subcortical and periventricular abnormalities with established lacunar infarcts and generalised atrophic changes.

Genetic testing confirmed the diagnosis of CADASIL with the presence of a heterozygous c.994C>T (p.Arg332Cys) mutation in exon 6 of the NOTCH 3 gene.

We report the first case of coexistent bilateral internal carotid artery agenesis and CADASIL. This case highlights the need to consider CADASIL in patients with cerebral subcortical and periventricular imaging abnormalities even with coexistent large vessel pathology.