What does occult neuroblastoma mean?

Neuroblastoma: I have not heard of the term "occult" neuroblastoma - a patient either has a neuroblastoma or does not, the use of the term "occult" is not typically used here.

Can't find primary..: This term has been used for children who present with opsoclonus (irregular rapid eye movements) and myoclonus (muscle twitching) due to a presumed antibody generated by the immune system that recognizes neuroblastoma cancer cells as well as normal tissues in the body (resulting in the opsoclonus and myoclonus); however, the neuroblastoma is so small that it can't be seen by imaging (=occult).