Acquired os odontoideum: a case report and literature review

Abstract

Os odontoideum has been defined as an independent ossicle, with smooth margins, separated with the base of the odontoid or the axis vertebrae [7, 15–17]. Since Giacomini first described os odontoideum in 1886 [10], its etiology has remained controversial. Supporters of a congenital etiology have considered os odontoideum as a segmental anomaly resulting from fusion failure between the odontoid and the axis vertebrae [2, 3, 8]. Moreover, several case reports of familial os odontoideum have been reported in support of their theory [1, 14, 18, 24]. Recently, we reported a threegeneration family with three members who presented os odontoideum [30]. In contrast, proponents of an acquired etiology state that the ossicle results from an unrecognized fracture or a cartilaginous injury of the odontoid followed by alar ligament contraction and interruption of the blood supply [7, 11, 29]. In support of the acquired theory, Verska et al reported one identical twin with an os odontoideum after documented trauma and the other twin with a normal odontoid and no traumatic history [27]. In the literature, proponents of the acquired etiology also reported 11 patients who had radiographic documentation of a normal odontoid and subsequently developed an os odontoideum after trauma [6, 7, 9, 12, 20, 22, 26]. The previously reported cases are summarized in Table 1. Most of these os odontoideum cases with a pretraumatic normal radiograph were present before CT scans were available. Obviously, solely based on plainfilm evaluation, the possibility of congenital deficits cannot be totally excluded. To our knowledge, the present case is the 12th case reported of posttraumatic os odontoideum who had radiographic documentation of a previous normal odontoid process in the English literature. This case report demonstrates a posttraumatic os odontoideum using reconstructive CT imaging, which has yet to be reported. The family was informed that data concerning the case would be submitted for publication, and consent was obtained.