A rare developmental variant of the atlas.

Congenital anomalies of the arch of the atlas in the sense of clefts are uncommon. As such anomalies may be mistaken for fractures, radiologists should be aware of them. A case of aplasia of the right part of the posterior arch producing wide, asymmetric medial cleft of the atlas is presented. The patient also had hypoplastic left part of the arch with the lateral cleft formed by a secondary ossification centre in the posterior tubercle. This combination of anomalies has not formerly been presented in literature.