That is surprising information. I have never heard anything like it before. My research shows DAI as a common subset of PCS. The shaken baby/car accident can cause the same physical forces as a contact with an external object. Most car accident brain injuries are due to impact with an external object, i.e. A pillar, B pillar, roof, windshield, dash board. DAI is known to result from any traumatic impact or shaking of the brain.

All of my injuries have been along a single axis with a very minor rotational component. The coup contra-coup forces of a linear impact (concussion) have similar damaging effect as a rotational injury. If the linear force is strong enough, there is axonal tearing between the lobes and the corpus colosum and milder axonal tearing between lobes and within lobes. LOC (loss of consciousness) has proven to be a leak indicator of outcome except for those in a coma.

Many times, an impact with an external object can have both a linear component and a rotational component. As the head is whipped forward, it is stopped by the object. It was rotating about the axis of the neck and moving forward. The forward motion is stopped by the object and the rotational motion is stopped by the object.

A hockey illustration could be this. The player has his feet swept out from under him by a clipping motion (hit behind and below the knees)As he falls back and to the ice, his head has a vertical down component. He probably tuck his chin to his chest in a reflex action. As his back hits the ice first, his head rotates about his shoulders/neck with his forehead moving down and his chin moving horizontal away from his chest. This rotation stops when his head hits the ice. The downward impact (which is much more severe) also stops at the ice. Both may have a contra-coup response if the head bounces. This has the effect of doubling the impact force to the brain.

As you can see, there are both rotational and linear forces with contra-coup forces.

It appears your docs use the same information source as WIKIpedia. If you read beyond the first paragraph, it become obvious that the first paragraph does not fit with the rest of the information. Most articles about DIA and PCS overlap them greatly. In fact. mild DIA is often referred to as the cause of PCS. PCS is actually a cluster of symptoms that manifest days to months after the impact. DIA is the physiological damage done as a result of the insult, some immediately, some as a longer term result of cellular changes.

This discussion only shows how much of the PCS/DIA arena is still uncertain. Doctors, whether M.D. or Ph.D. or Psy.D. try to sound authoritative with whatever information they have gathered. A broader investigation shows how problematic it is to be authoritative with the lack of understanding even in the finest research studies.
They are right about the permanence of DIA. But PCS has permanent symptoms too. Neuro-plasticity can only go so far. DIA means a wide area of damage. Hard to rewire around such a wide area of damage.

<While they share some common symptoms, my neurologist and neuro-psychologist both consider PCS and DAI different conditions.

There are quite a few distinctions but here are the big ones:
1. Manner of injury: DAI is caused by the violent rotation of the brain inside the cranium (shaken babies, car accidents, etc...) as opposed to contact with an external object.
2. Unconsciousness: Unconsciousness is a major indicator of DAI. Ninety percent of DAIs never regain consciousness. The ten percent of us lucky enough to wake up have severe impairments compared to our pre-morbid function.
3. Damage: As opposed to PCS where damaged can be localized (focal point), DAI causes significant damage to all areas of the brain. In scans, the DAI brain shows considerable shrinkage and torn and damaged axons in all lobes.
4. Diffuse axonal injury is permanent. There is little improvement over time, even with therapy. >