Lindsay is a student in Mr. Wagner’s Kindergarten class. She was born under average conditions and met all of the appropriate developmental milestones as she progressed into toddlerhood. She attended a private pre-school program at a local child care facility. Her pre-school records indicates that she was performing tasks at an age-appropriate pace. During the summer between her pre-school program and entering Kindergarten, Linsay and her mother were in a car accident. While Lindsay showed no signs of external trauma, she was hospitalized to control some minor brain swelling and to monitor her severe concussion. Lindsay’s mother did not disclose any of this until Mr. Wagner called her in to discuss some discrepancies between Lindsay’s academic skills this year and those from her years in pre-school. She still has appropriate social skills, and her deficits do not seem to manifest until complex, academic skills are introduced. Which of the following medically-related issues should be considered and evaluated first as a possible cause for Lindsay’s skills regression?