Congenital absence of the anterior arch of the atlas: a normal variant

Congenital absence of the anterior arch of the atlas is incredibly rare with only two cases reported previously in the literature. We present a third case of a medically fit patient who suffered neck trauma with an abnormal odontoid peg x-ray, which subsequently demonstrated a congenital non-fusion of the anterior vertebral arch of C1 on computed tomography. This case highlights the need to have an open diagnosis to include congenital anomaly when interpreting abnormal odontoid peg x-rays.