Challenging the diagnosis of a posterior circulation dissecting aneurysm

I ntracranial vertebral dissections have polymorphs clinical presentations and can lead to haemorrhagic complications if they are intracranial. We here describe a case of a thrombosed dissecting aneurysm of postero-inferior cerebellar artery (PICA) revealed by a Wallenberg syndrome preceded by headaches.A 23-year-old patient, without neurological or vascular past medical history, was admitted for dizziness preceded by headache. The clinical examination on admission revealed an incomplete Wallenberg syndrome, associating hemiface sensitive deficit, Horner's syndrome, dysmetria and nystagmus. The brain MRI showed a latero-medullary infarct with a homolateral PICA thrombosed dissecting aneurysm.The diagnosis of intracranial dissecting aneurysms needs particular caution because aneurysm sac thrombosis can give false reassurance on angiographic MR sequences. Moreover, the anatomic features of intracranial artery walls make them prone to sub-adventitial dissection and subsequent subarachnoid haemorrhages. Therefore, antithrombotic therapy should be used with caution, due to the risk of bleeding in these intracranial dissections.