A two-month-old infant presents with irritability and lethargy. The parents state he was well until he rolled off the couch onto the floor on the previous day. On examination, he is inconsolable and afebrile. The fontanels are full and tense. He has a generalized tonic-clonic seizure in your office. The most impoant additional diagnostic study is:

Though infection must be considered as an etiology, acute trauma is more likely in this scenario. This case represents the classic picture of the shaken baby syndrome, which produces intracranial trauma without obvious external findings. This infant is critically ill and lacks preceding illness or constitutional symptoms. The tense fontanelle reflect increased intracranial pressure. A retinoscopic exam most often would reveal retinal hemorrhages that would confirm the diagnosis. A history of trauma, which does not correlate with the child's injury should ale health care providers to the possibility of child abuse. Ref: Ropper A.H., Samuels M.A. (2009). Chapter 35. Craniocerebral Trauma. In A.H. Ropper, M.A. Samuels (Eds), Adams and Victor's Principles of Neurology, 9e.