The Incidence and Clinical Implications of Congenital Defects of Atlantal Arch

Congenital absence of the posterior arch of the atlas associated with a fracture of the anterior arch

“…A CT scan is helpful in evaluating the integrity of the atlas and differentiating an acute injury from a developmental cleft. 3 It is unclear as to whether this is a hereditary defect, although two reports have documented the existence of cases involving a mother and son. 1,4 The incidence between genders is similar and the clinical presentation is variable.…”

Atlas occipitalisation associated with other anomalies in a 16th century skeleton from Sardinia (Italy)

“…In modern clinical studies type A defect was seen with an incidence of 2.6% [17] to 3.2% [7]. Posterior arch defects are attrib-uted to the defective or absent development of the cartilaginous preformation of the arch rather than a disturbance of the ossification [11]. Congenital posterior arch defects are generally asymptomatic and are considered benign anatomical variations; however, as in asymptomatic individuals they may become dangerous in the context of trauma, it is important to distinguish between a bony injury and a congenital anomaly [10].…”

A case of combined congenital anterior and posterior arch anomaly of C1 vertebra

“…This indicated that the finding was not acutely caused by recent trauma. Lateral flexion/extension plain radiographs of the cervical roughly 4% of patients present with congenital posterior arch defects, with the predominant (97%) type being Type A [1,4,5]. Type B through Type E congenital defects have been reported to occur in 0.69% of the population [1].…”

“…A secondary center of ossification center which is the center for the posterior tubercle, may be present in about 2% of cases. Failure in any step of this complex process leads to abnormalities [1,3,4].…”

“…These anomalies develop in intrauterine life as a result of developmental failure of chondrogenesis which may variate from partial clefts to total agenesis of the atlas rings [1][2][3]. In patients with a history of trauma, these anomalies can mimic an injury of the craniovertebral junction (CVJ) [1,4].…”