An interesting article will appear in the October issue of the journal of Forensic Science International. It is titled: Mast cell reactivity at the margin of human skin wounds: An early cell marker of wound survival?
Let me explain.
First of all, this article deals with very sophisticated biochemistry in that they measured the activity of certain esterase enzymes in relation to time after injury. I won’t attempt to explain it, but simply point out that research is ongoing in this distinctly forensic arena. But it does bring up the question of how the ME can judge whether a wound occurred pre-mortem or post-mortem.
This is sometimes one of the most difficult determinations the ME must make and his opinion impacts many things. For example, let’s say two assailants attack a victim. One shoots him three times in the abdomen, the other stabs him in the chest after he falls to the ground. Which injury killed him?
Sometimes it’s obvious from the nature of the wounds and the organs and blood vessels injured by each wound. At other times it’s not so clear. One key determination is whether the victim was dead before the stab wound occurred or not. If so, the second assailant might dodge a murder charge; if not, then the stab would could be the proximate cause of death or could at least be a contributing factor, in which case he could face serious charges.
The ME would analyze the stab wound. If it is clean and without irregular edges he can state that the victim was not wiggling or struggling at the time of the injury and just might have been dead beforehand. Living folks tend to fight back and try to avoid stab wounds and this struggle is often reflected in the character of the wound. Dead people tend to lie still so that the wounds are clean, in and out.
If there is no bruising or bleeding into or from the wound, the ME would know that the heart had stopped and there was no blood flow before the wound occurred. If bleeding occurred, the heart must have been beating and the blood flowing at the time of the injury.
Sometimes this is all he needs, but sometimes this type of evidence isn’t clear.
So, what are mast cells and what do they have to do with this?
Whenever an injury occurs, several types of cells rush the area to begin the healing process. Platelets in the blood arrive and begin to clump together and plug any breech in the blood vessels. This action is the first step in what we call the Clotting Cascade, and without it blood clotting would not occur and even minor injuries could cause lethal bleeding. White blood cells, lymphocytes, and mast cells also appear.
Mast cells contain little packets of chemicals–histamine and certain enzymes–in their cytoplasm–the liquid part of the cell. When an injury occurs the mast cells move in and release these chemicals. When properly stained and viewed under a microscope the cytoplasm of a mast cell is filled with tiny blue granules. These are the chemical packets. As the chemicals are released, the granules disappear, a process known as degranulation. This only happens while we are alive. After death the mast cells do not degranulate.
Mast Cells: The large blue blobs are the nuclei and the tiny blue dots in the cytoplasm of these cells are the granules.
To determine if a wound was pre- or post-mortem, the ME can excise some tissue from near the wound edges, stain it, and look at it under the microscope. If the mast cells have degranulated he will know that the victim was alive at the time of the injury; if not, he will know just the opposite.
This type of examination is rarely needed, rarely done, and can offer confusing results in some cases, but it is an interesting technique for determining the timing of a victim’s wounds.