Is it possible for shaken baby syndrome to occur and there be no symptoms? or are there always going to be some symptoms?

As a definition=no: SBS refers to the outcome of the to & fro excursion the head makes when a baby is violently shaken not the act of shaking a baby. It implies brain injury severe enough to result in impaired function of the brain & the body systems it controls. No symptoms= no brain injury. The process can go unrecognized in the moments after the injury, but within minutes/hours it will become evident.

Dilate the eyes.: SBS is difficult to diagnose, but intraretinal hemorrhages or vitreous hemorrhages can be a clue, even when the neuroradiologic scans are negative.