[Spontaneous internal carotid artery dissection as a cause of unilateral lower cranial nerve palsies].

We present a 60-year-old man with a complete right IX-XII nerve palsy (Collet-Sicard syndrome) due to spontaneous right internal carotid artery (ICA) dissection. Magnetic resonance imaging (MRI) and MR angiography (MRA) showed signs of subadventitial dissection of the right ICA with a mural haematoma that expanded the circumference of the vessel at the level of the retrostyloid space, adjacent to the IX-XII nerves. No narrowing of the lumen or aneurysms was found. Clinical recovery was excellent after treatment with only antiplatelet drugs. Cervical internal carotid artery dissection should be included in the differential diagnosis of lower cranial nerve palsies. MRI and MRA are noninvasive, reliable methods for diagnosis and follow-up, especially in subadventitial dissections.