Final answer:
Spina bifida occulta is usually detected by an X-ray, which can identify abnormalities in the vertebral column.
Step-by-step explanation:
The initial diagnostic evaluation to detect spina bifida occulta is usually an X-ray. Spina bifida occulta is the mildest form of spina bifida, where the vertebral bones do not fully surround the spinal cord. This condition is usually asymptomatic, and an X-ray can help identify any abnormalities in the vertebral column.