posterior arch defect

The radiographic image demonstrates a classic presentation of spina bifida occulta affecting the first sacral vertebra (S1), highlighted by the red circle. This congenital anomaly results from a failure in the normal embryological development of the neural tube, specifically inadequate formation of the vertebral arch components.

The CT scan image displays an axial view of the first cervical vertebra (C1), also known as the atlas, with a notable unfused posterior arch highlighted by the red arrow. This congenital anomaly represents a failure of proper fusion during embryonic development of the posterior neural arch components.