We read with great interest, the article by Tsuang et al. (Occipitocervical malformation with atlas duplication) published in the Journal of Neurology, Neurosurgery and Psychiatry (2011 82:1101-1102). In this report, a patient with spastic gait is presented. The imaging studies revealed an atlas-like vertebra below the occipital bone. The authors referred to this anomaly as "atlas duplication". However, we believe that the anomalous vertebra is in fact a "persistent proatlas". The proatlas is found in some lower vertebrates as a separate, atlas-like vertebra between the occipital bone and atlas (Rao, 2002; Scheuer and Black, 2004). In man and during the embryonic period, the occipital sclerotome 4 is segmented in a manner that its proximal portion (hypochordal bow) is integrated into the caudal part of the basiocciput and its distal portion is integrated to the odontoid process of axis (Muller and O'Rahilly, 2003). Although proatlas segmentation malformation has been described in man, the "persistent proatlas" has never been reported before. We would like to congratulate the authors for recording this historically significant observation, which will remain a landmark in the developmental anatomy of the craniovertebral junction. References Rao PV. Median (third) occipital condyle. Clin Anat 2002;15:148-51. Scheuer L, Black SM. The Juvenile Skeleton. San Diego, CA: Elsevier Academic Press, 2004, p. 195. Muller F, O'Rahilly R. Segmentation in staged human embryos: the occipitocervical region revisited. J Anat 2003;203:297-315.

Conflict of Interest:

None declared