[QUOTE=Waverly]
No need to apologize to me. This is still an at-will participation site.
I understand the literal gliding you are describing, but isn’t this an abrasion?Yes, correct, but I don’t understand it to be specific only to the parasagittal veins. If you have a non-standard definition given to you by a mentor, I can accept that.
Now, would an acceleration of 9.8m/s/s (presuming he died on this planet!) be likely to cause such an abrasion? If so, I might have to rethink my next dive into a pool. There is, of course, a much more rapid deceleration, but that is when the more commonly defined contusion takes place.Yes, I’m familiar with the concept, though I can’t say I am closer to understanding why one would look for a contrecoup injury in response to finding an abrasion on the underside of the brain. In the case of a fall, the thing I’d be most interesting in finding is the coup contusion. Contrecoup or either type of gliding contusion might be present in some circumstances, but it would be rare not to find a coup contusion. Or, I should say that’s the way it looks to me. I’m not an expert.
Did I just botch the autopsy? Is the buzzer going off and the nose glowing red?
[/QUOTE]
Well, I can’t say you botched the autopsy, but what you say above certainly isn’t in the mainstream of what’s been observed about head injury for the last six or eight decades. I can tell you what I’ve been taught and what I’ve observed at many, many posts. I can’t really tell you why it happens, because people much more expert than I are arguing over why it happens. But I can tell you what I’ve seen, and how we know from the autopsy without any need for witnesses when it’s coup and when it’s contrecoup.
OK, lecture on coup and contrecoup coming, with actual case studies.
Goes like this. Man is cleaning a slick and slippery metal grate over a chicken parts collection vat set into the floor at MmHmMm poultry processing plant. He is encased in plastic protective coverings over his work clothes. His plastic-coated boot slips on the ckicken-fat-coated grate. His feet go in the air, he falls with an acceleration of 32 feet per second per second (forgive me for English units - America clings so touchingly to the old ways). The back of his head hits the grate hard enough to split his scalp for 2 inches either direction. He falls unconscious into the vat. His unconscious body naturally makes breathing motions, and he asphyxiates on chicken fat.
(Yes, this was one heckuvan autopsy - I used infinite quantities of Simple Green and never got all the fat off him)
At autopsy, there is a spill of blood underneath the occiput of his scalp, associated unsurprisingly with the 2" laceration. There is no skull fracture in the occiput; it’s completely intact.
Open the skull, there is no blood over the brain at the occiput. Dry as a bone. Take the brain out, there is a thin film of subarachnoid blood across the inferior aspect of the frontal and temporal lobes, and there are fresh contusions across the same areas, deepest and worst in the areas that stick out the most and that hit the forwardmost – the frontal and temporal tips. There’s a ramifying hairline fracture through the right supraorbital plate - the thin plate of bone that overlies the right eyeball and keeps it separate from the brain. When I was lent a skull to study at the start of medical school, they warned us strongly about those bones and the ethmoids: they’re fragile! Don’t break 'em! They’ll crack!
So here we have a head with a serious injury to the back, and a brain with serious injury to the undersurface and the front. This is classic contrecoup injury. It is found in people who sustain a major fall, typically from standing. It is classic for the contusions to be found across the undersurface of the brain in front.
The simplified explanation for contrecoup injury is that the sudden deceleration of the head as it comes to a stop against the hard surface of the metal grate causes the brain to rebound away from the site of injury, and injure itself against the inside of the skull, on the opposite side. This makes sense to me. It certainly explains why the supraorbital plate cracked - from the impact of the brain hitting it. Why only on one side? The impact was slightly to the opposite side on the back of the head. Not exactly in the midline.
If you are wondering why, with a blow on the back of the head, the brain injury is seen only on the undersurface of the front of the brain, it’s because the brain is more tightly tethered to the skull on the undersurface, due to the brainstem and the cranial nerves; and has more room beneath the dura on the top. So it can slide past the bony arches of the inside of the top of the cranial vault, but bounces and jounces across the rough ridges beneath it.
The sine qua non of contrecoup injury is blood beneath the scalp (at the site of impact) on one side, injury to the brain on the other side. As I said, this idea of the brain bouncing to the opposite side of the cranial cavity because of sudden deceleration is the best explanation I’ve been offered; but I do understand that the arguing about the actual physics that explains this repeatedly observed finding is well beyond me.
Now. I don’t want to discuss any cases of fatal coup injury, since all the ones I have had are homicides. So I’m going to give you a hypothetical based on many autopsies. Imagine the same man, magically restored to health, standing looking nervously around him on a street corner. A member of a rival gang runs up to him and grabs his arm. He throws him off, but while their arms are going back and forth, another gang member rushes up with a two-by-four, and cracks him as hard as he can over the back of the head. The man collapses to the street. The two assailants run off. It takes a while for him to be discovered; when the ambulance comes, he cannot be resuscitated.
At autopsy, there may or may not be a laceration to the scalp across the occiput (probably would be, in the case described), but there will definitely be blood beneath the scalp at the site of injury. And there will be subarachnoid blood across the occipital lobes, and fresh occipital contusions. This is classic coup injury. Blood beneath the scalp is on the same side as blood across the brain and blood within the injured portions of the brain.
I have not seen contrecoup injury sustained in people who dive. This may be because the resistance of the water provides significant braking. Even though your acceleration through the air was at least 32 feet per second per second, and maybe more if you bounced up from a board to make a nice swan dive, you are likely decelerating through the water. The speed of vessels through air versus across land versus through water is considerably different, and there’s no reason why your body shouldn’t be slowed down far below 32 ft/sec/sec by the resistance of the water.
However, I have seen deaths in people who dove into shallow water. I remember one very tattooed fellow who was only three days out of jail. He was last seen performing tai chi like exercises on the waterfront near the hoity toity beach club. He was found floating in the water. At autopsy, a small abrasion on the undersurface of his chin; no other external sign of injury. Internally, a broken neck, with the direction of fracture showing it was hyperextension injury. That is, he landed on his chin, and bent his head back so far it broke his neck. Death was immediate, and was not related to any of his other conditions, such as his emphysema, his heart disease, or the fact that his blood toxicology was positive for both marijuana and cocaine.
I have chosen real cases (with identifying data I hope fully removed) so that you can feel this is a real observation. But I have to reiterate how often coup and contrecoup injury have been a repeated observation for many decades of forensic inquiry. That’s why we testify on them in court like that. Blood on one side of the head, brain injury and subarachnoid on the opposite side: contrecoup, or roughly “opposite to the blow” if you take liberties with the French. Blood and injury on the same side, coup, or blow. One implies fall with sudden deceleration of the whole head. One implies impact from a hard object with sudden deceleration of the object only, at a focal point on the head, likely with brief subsequent acceleration of the whole head.
I used only occipital as my example here, with inferior frontal and temporal contusions, because that is by far the commonest contrecoup injury seen. But I have also seen contrecoup injury where the bloody impact site was beneath the skin of the forehead, and the brain injury was in the occipital lobes; and where the site was left temporoparietal, or above the ear, and the brain injury was right temporoparietal. It can happen anywhere in the head.
Hope we agree on the terms,
gabriela
