What kind of complications might happen from a lumbar CT scan without dye?

Shouldn't be any. Thos is a non-invasive imaging procedure with little risk of complication. A ct scan uses x-rays taken in a spiral fashion to create an image that is 3 dimensional. A single ct scan is roughly equivalent to 200-300 chestherefor, therefore in people who are imaged hundreds of times over a number of years, there is a small risk of radiation exposure causing cancerous change in cells.