Hyoid-related internal carotid artery dissection

Abstract

A 30-year-old man without cardiovascular risk factors presented, after 1 week of right-sided anterior neck pain, with acute left hemiplegia immediately after heavy weight lifting (i.e., removing large boxes filled with books with the head in mid-position without rotation). There was no recent history of head or cervical trauma. Brain MRI showed an acute infarction in the right middle cerebral artery territory. Carotid duplex examination revealed a high degree of stenosis of the right internal carotid artery, which was confirmed by CT angiography showing a segmental tapered narrowing of the right internal carotid artery located just lateral of the greater horn of hyoid bone, in the absence of atheromatous plaques (Fig. 1). Fat-saturated T1 MRI showed the presence of an intramural hematoma in the right internal carotid artery. A diagnosis of carotid dissection, in absence of clear head/ cervical trauma was made, and anticoagulation treatment was started. CT angiography also showed a 90-mm-long bilateral elongated styloid process (Fig. 1). However, the tip of the elongated styloid process was located at 9.1 mm of the right internal carotid artery, and the smallest distance between the body of the elongated styloid process and the right internal carotid artery was 3.5 mm, making impingement of the carotid artery by the styloid process, even with head rotation or flexion, unlikely. Another abnormality was noticed on CT angiography, consisting of an elongated hyoid bone resulting in a extremely reduced distance of 1.6 mm between the anterior tubercle of the transverse process of the third cervical vertebra and the greater horn of the hyoid bone (Figs. 1, 2). Three months later, CT angiography revealed complete recanalization of the right internal carotid artery (with a diameter of 4.5 mm at the level of the greater horn of the hyoid bone), now located medial of the greater horn of the hyoid bone (Fig. 2). Carotid duplex examination showed normal velocities, in the absence of changes in velocities after head rotation. We hypothesized that intermittent change in position of the internal carotid artery (diameter 4.5 mm) through the small space (1.6 mm) between the third cervical vertebra and the hyoid bone may have provoked the arterial dissection, although carotid injury due to the elongated styloid bone could not be excluded. In a vast portion of patients with carotid dissection, there is no clear history of head or cervical trauma. The exact cause of these, so-called spontaneous, dissections is unclear. Recently, certain anatomic characteristics of the styloid process (i.e., the length and the proximity to the carotid artery) have been reported as potential risks factors for carotid dissection [1]. The stylohyoid complex consists of the styloid process, the stylohyoid ligament, and hyoid bone. Pathological conditions (called the stylohyoid complex syndrome) associated with these structures, which can include an elongated styloid process, ossified stylohyoid ligament, elongated hyoid bone, or combinations of several of these conditions (like in our patient with both elongated styloid process and elongated hyoid bone) can cause cervical and pharyngeal symptoms, probably related to irritation of the structures around this complex (including the carotid arteries and the cranial nerves VII, IX, and X) [2]. D. Renard (&) Department of Neurology, CHU Nimes, Hopital Caremeau, Place du Pr Debre, 30029 Nimes Cedex 4, France e-mail: dimitrirenard@hotmail.com