What defines a spina bifida as spina bifida occulta?

Skin covering: Spina bifida occulta, like open spina bifida, is a congenital malformation involving a problem with closing of the neural tube during development. However, there is not exposed neural tissue in spina bifida occulta. There can be tracts connecting the skin to the spinal cord, or lipomas or bands (tight filum) which can cause neurologic deficit. There can also be bony issues.