The infant's head is disproportionately larger and heavier relative to the rest of the body. It is supported on a relatively shorter, weaker, and more flexible neck. Force applied to the head or body results in more momentum of the head and less restriction from the weaker cervical soft tissues. This increases the likelihood of injury to the brain. In infancy, the open fontanelles and sutures provide more flexibility, which can absorb greater impact as well as provide for expansion of the intracranial volume. Incomplete myelinization results in greater plasticity of the brain. This flexibility allows for more distortion between the container (the skull and dura) and its contents (the brain and the cerebral blood vessels), which results in increased susceptibility to hemorrhage. Most head trauma results from a combination of direct impact, acceleration/deceleration, or rotational shear forces. The more pliable skull of the younger child tends to bend inward on impact, applying pressure on the inner table and its underlying vessels in the epidural and subdural spaces. The surrounding areas bend outward, putting pressure on the outer table, producing a fracture which may or may not be proximate to the area of impact. Younger children and infants with isolated skull fractures tend to present with normal mental status unless there is a significant underlying brain injury with mass effect. Laboratory studies suggest that concussive brain injury is characterized by transient, functional, cellular impairments, including abrupt neuronal depolarization, release of excitatory neurotransmitters, ionic shifts, changes in glucose metabolism, altered cerebral blood flow, and impaired axonal function. Any of these conditions may lead to a state of enhanced vulnerability, during which time the patient may have symptoms of confusion or headache. A second impact before the brain is fully recovered may result in a potentially fatal loss of cerebrovascular autoregulation resulting in vasoparalysis, brain swelling, increased intracranial pressure, and death (second impact syndrome). Research indicates that, after a single brain impact, this state of increased vulnerability can persist for 3 to 5 days but usually resolves within a week. In the patient with a mild head injury, a more prolonged “postconcussion syndrome” may occur, characterized by persistent alterations in cognition, behavior, and personality changes as well as emotional swings. This can affect interpersonal relationships, school, and work. Athletes reporting posttraumatic headache up to 7 days after injury demonstrated significantly worse neurocognitive scores, possibly associated with incomplete recovery. Chronic cognitive impairments can occur in athletes who have sustained multiple, seemingly minor, head injuries and are associated with accelerated or increased neurodegeneration in specific brain regions. Clinical symptoms of concussions (confusion, amnesia, headache, attention deficits, disorientation, and loss of motor coordination) are usually transient.5