It can be difficult to define mild traumatic brain injury (mTBI). Features such as age, sex, education, psychological history, or medical history can lead to differences in symptom reporting. The pathology of mTBI is unclear and can be different depending on the bio mechanics that caused the injury (accelerations/deceleration, direct blow, rotation). There is further difficulty in that symptoms can be quickly alleviated in some case, but persist for several months in other cases.
There is currently some disagreement on the definitions of mTBI and post-concussion syndrome (PCS), as well as what factors contribute to PCS and why. A recent paper offered the following definitions for clarification:
mTBI can be defined as "an essentially reversible syndrome without any detectable pathology," in which symptoms can include headache, dizziness, nausea, unsteady gait, slurred speech, and poor concentration. Clinical indicators can include a GCS of 13 or higher and post-traumatic amnesia of no more than 24 hours.
PCS is the "constellation of symptoms in physical (eg fatigue, headaches), cognitive (eg difficulties with concentration and memory) and emotional (eg irritability, anxiety) domains that persist weeks, months, and even years after an mTBI."
Williams WH, Potter S, & Ryland H. Mild traumatic brain injury and post-concussion syndrome: A neuropsychological perceptive. Journal of Neurology, Neurosurgery & Psychiatry. (September 2010).