Forensic pathology

Forensic pathology is figuring out why people died. If possible... you figure-out when and how.

Manner of death

Manner

Homocide

Suicide

Natural

Accident

Undetermined

Notes:

• Undetermined - is a waste basket category.
• Homocide - not necessarily murder.

Cause of death

If the death is natural:

• It should be a medical diagnosis - not the mechanism (e.g. cardiac arrest, cachexia, kidney failure).
• The mechanism is irrelevant.

Notes:

• Cancer is rarely the immediate cause of death - it is usually something else.
• Things (mechanisms) that shouldn't be used: http://www.pallimed.org/2008/03/unacceptable-causes-of-death-other-web.html
• A Nice summary: http://www.eperc.mcw.edu/fastFact/ff_155.htm

Legal frame work

• In Ontario, the manner is determined by the coroner.
• Coroners, in Ontario, are MDs -- usually family docs.
• The cause (e.g. "gunshot wound to the head") is determined by the pathologist.

NB - the word coroner is not synoymous with MD. British Columbia has coroners that aren't MDs.

Forensic triangle

Most general differential diagnosis:

• Natural:
  • Infection (e.g. pneumonia),
  • Infarction (e.g. MI),
  • Haemorrhage (e.g. cerebral, GI).
• Toxic:
  • EtOH,
  • Illicit (e.g. cocaine, heroin, LSD),
  • Rx,
  • Over-the-counter (OTC) (e.g. acetaminophen, warfarin),
  • Poisons.
• Trauma:
  • Gunshot wound (GSW),
  • Blunt force trauma,
  • Sharp force trauma,
  • Asphyxial,
  • Environmental (e.g. hypothermia, hyperthermia, drowning, lack of oxygen).

Difficulties arise when more than one point of the triangle is in play, i.e. the forensic pathologist has to earn their pay when an old man with a heart condition is known to be into erotic asphyxia, and dies after doing some drugs and whilst indulging in erotic asyphxiation with a friend...

• If he had an MI and there was no stressor... natural death.
• If he over did it with the drugs, it is an overdose, ergo accidental.
• If he did the erotic asphyxia a bit too long it is accidental.
• If the friend held the plastic bag over his head just a bit long to asphyxiate him... it is a homicide.
• If he was a lone and depressed... he might have been trying to kill himself, ergo suicide.

Death

Rigor mortis

Def'n: muscle rigidity following death (caused by depletion of ATP).

Dependent on:

• temperature of patient at death.
• temperature variations in the environment since death.
• presence of some medical conditions.
• may never develop!

Summary: Its onset & presence is highly variable. Therefore, it is only marginally useful for determining the time of death.

A crude guess for time of death based on rigor:

• Warm & flaccid <3 h.
• Warm & stiff 3-8 h.
• Cold & stiff 8-36 h.
• Cold & flaccid > 36 h.

Livor mortis

Def'n: pooling of blood in the dependent position, due to blood stasis.

• Onset may preceed death in the context of congestive heart failure.
• If pressure is applied to a dependent area-- no blood can enter there; thus, a pressure area is blanched (i.e. white).

• Can be seen externally, i.e. on the skin, and internally.
• Liver mortis becomes fixed some time after death.
  • Liver mortis does NOT tell one the position the decedent was in at the time of death-- only the position the decedent was at the time liver mortis became fixed. If the decedent wasn't moved liver mortis can help determine the position the person was in when they died.

Classification of wounds

Mnemonic CALI:

• Contusion - "bruise", haemotoma
• Abrasion - "scrape", e.g. motorcyclist slide across the roadway... skin ripped-off
• Laceration - "tear", trauma distant from where skin split
• Incision - "cut", e.g. caused by a knife

How to decide what you're looking at:

• Contusion:
  • Can be demonstrated histologically... there are extravascular RBCs.
    • If pre-morten there is vital reaction, i.e. WBCs come to clean-up the trauma.
  • If the post mortem interval is not known and long-- differentiation from decomposition may be non-trivial/impossible.

• Abrasion vs. contusion:
  • Contusions skin is intact... in abrasion it is not.
  • Abrasions and contusions may be co-localized, i.e. in the same place.

• Laceration vs. incision:
  • Lacerations have "bridges", incisions do NOT have bridges.
    • Bridges are fine strands of tissue that cross the long axis of the skin defect.
      • You can think of the wound as partially "sutured" by the bridges of tissue.

Autopsy

Forensic vs. hospital

Forensic autopsies are focused on the external exam.

Hanging

Classic:

• V-shaped furrow on the neck.
• V "open" at the point of suspension.

Drowning

Classic:

• Autopsy is often negative, i.e. there is no anatomical cause of death.

Drowning is difficult to prove on autopsy. The diagnosis is often based on circumstance, i.e. the scene.

Macroscopic

External:

• Plume of froth at the mouth/nostrils (fresh drowning only).

Internal:

• Lung emphysema.
• Froth in the trachea.
• Patlauf spots -- ???

Micro/Lab

There are a few tests of debated value:

• Diffusion of particulates into the blood (left ventricle) from the water.
  • Diatom test.
• Haemodilution.
  • Mostly useless - CPR interferes with it, not reliable if there putrefaction or autolysis.
• Transport of aveolar element into blood circulation.

Carbon monoxide

Carbon monoxide (CO) is a common way to commit suicide.

Pathophysiology:

• CO binds to haemoglobin -- prevents oxygen from binding there.

Findings:

• Salmon pink skin.
• CO level (blood test) elevated (???).

Gunshot wounds

Number of entrance wound should equal the number of exit wounds -- if it doesn't there are:

• Bullets in the body,
• "Tandem bullets" -- two bullets entered at the same place,
• Secondary projectile -- the bullet hit something, e.g. bone, and made it fly out of the body,
• You missed an entrance or exit,
  • Places to look:
    • Below chin (common in suicides),
    • In mouth (common in suicides),
    • Back,
    • ... anywhere the sun don't shine.

Firearm projectiles

Two broad groups:

• Shotgun projectiles.
  • Many small pellets.
• Handgun/rifle projectiles.
  • Similar in size to the barrel - large when compared to shotgun projectiles.
  • Bullets from handguns/rifles are marked by the barrel on the way-out (by grooves which in part spin on it to improve accuracy).

• Bullets are often good evidence:
  • The calibre (size) and markings from the barrel (on handgun/rifle projectiles) allow it to be match to the weapon that fired it.
  • Thus, all projectiles are recovered from a body... and it is routinue to X-ray all gunshot victims.

Entrance wounds

Characteristics:

• Circular/round defect --especially if the projectile strikes at a right angle to the surface.
  • If the projectile strikes at an angle the injury will be elliptical and the long axis of the ellipse will lie approximately in the plane the bullet traveled.
• An abrasion, or scraping, --concentric or eccentric-- usually surrounds a deep wound (key feature -- used to differentiate from exit wounds).
  • Eccentric abrasion suggest directionality.
• Usually smaller than exit wounds.
  • In skull the inner table defect is typically larger than outer table defect ("internal bevel").

Atypical entrance wounds:

• Irregular (non-circular/non-elliptical) margin.
  • May be due to close range/contact.
    • Classically results in a "stellate" pattern.
  • Bullet ricochets --hits other object before hitting target, gun defective -- bullet's long axis doesn't coincide with its velocity vector.
    • Classically results in a "D-shaped" wound.

Exit wounds

Characteristics:

• Wsually bigger than entrance wounds.
• Morphologic shape -- variable.
  • Round, stellate, ovoid.
• NO abrasion at wound margin (key feature).
• In skull -- outer table defect typically larger than inner table defect (external beveling).

Atypical exit wounds:

• "Shored" exit wounds.
  • Exit defect created whilst surface supported/adjacent to firm surface.
  • Supporting surface may lead to abrasion.
  • May appear to be an entrance wound.

Special entrance/exit wounds

• Keyed wounds.
  • Combination entrance/exit wounds -- result from a bullet grazing the victim.

Distance of shooter

Contact:

• Muzzle impression.
• Stellate splitting/tearing of the skin -- especially if it overlies a bony surface.
• Soot/gun powder residue - deep in the wound.

Close range:

• Stippling - punctate abrasions around the entrance wound.
  • Suggests a distance < 60 cm.
• Soot/gun powder residue - dirt at the entrance, can be wiped-off.

Distant:

• No soot.
• No stippling.

Note:

• Absence of soot & stippling does not exclude near range -- may be assoc. with clothing or intermediate target separated from the victim post-injury.

Manual strangulation

Gross findings:

• Hyoid bone fracture.
• Thyroid cartilage fracture.
• Haemorrhage in strap muscles of the neck.

Blunt force trauma

• Pretty much anything.
• Beer bottles are common... and strong enought to fracture a skull.
  • Empty bottles have a higher fracture energy than full ones.

Sharp force trauma

• Knife or other sharp object.

Considerations

Prinsloo and Gordon artefact = artefactual post-morten haemorrhage on the posterior surface of the esophagus.

Injury severity due to GSWs

The damage of a projectile depends on:

• Where the bullet strike, e.g. ascending aorta vs. brain vs. tibia vs. gluteus maximus.
• Kinetic energy of the bullet.
  • Ek=1/2*m*v^2.
    • Velocity is more important -- as it is squared (duh).
• Cavitation effect.

Aortic trauma

• Aortic dissection due to trauma is often catastrophic.
• Classic location of injury is subclavian branch point.

Dissections often classified as:

• Type A - aortic root to just distal of left subclavian artery.
• Type B - distal to (left) subclavian artery.

Head injuries

Diffuse axonal injury

General:

• Hypothesized to arise from high shear loading of white mater tracts.

Macroscopic findings:

• Tears - corpus callosum.
• Haemorrhage.

Microscopic findings:

• Axonal retraction balls.
• "Microglial stars".
• Degeneration of fibre tracts.

Excited delirium

General:

• Also known as "agitated delirium".
• Dx is considered controversial, especially outside of the forensic pathology community.
• The diagnosis has garnered considerable attention in the context of electroshock weapon use, as Taser International (a manufacturer of electroshock weapons) has blamed all deaths involving its weapons on it.

• There is no "official" definition for excited delirium.
  • Most agree it includes fever.

One paper defines it in relation neuroleptic malignant syndrome:

• Fever.
• Disorientation and confusion.
• Increased energy/superhuman strength.

Excited delirium - hypothesis:

• Thought to arise in the context of severe chronic mental disorders (e.g. schizophrenia) and protracted cocaine binges.
• Thought to result from alteration of dopamine receptor density. The D2 receptor in particular, which is thought to be important in temperature regulation, is decreased in psychotic cocaine abusers.

Toxicology

Cocaine

• No agreed upon toxic dose. (due to tolerance)
• Chronic use may lead to cardiac enlargement.

Natural death

There is a lot that can kill ya... but only a few of those are quickly, i.e. within a hour or so.

Generally, these things are:

• Cardiovascular:
  • Arrhythmia.
  • Myocardial infarction.
  • Haemorrhage.
    • Ruptured aneurysm.
• Respiratory:
  • Pulmonary embolism (PE).
  • Asthma.
• GI:
  • Haemorrhage.
    • Esophageal varices.
    • Gastric varices.
• Neurologic:
  • Intracranial haemorrhage.
    • Ruptured aneurysm.
    • Spontaneous subdural haemorrhage.
  • Stroke:
    • Haemorrhagic.
    • Thrombotic (more common than haemorrhagic).

Forensic entomology

Main article: Forensic entomology

• Study of the bugs that eat corpses.
• Bugs may hide a wound... it is important to know where they like to be.

Decomposition

According to textbooks one of two things happens post-mortem:

• Mummification, or
• Putrefaction.

Real life:

• A mix of mummification and putrefaction occur, i.e. part of the corpse is mummified... part of it decomposed through putrefaction.

Mummification:

• Predominant in dry environments.
• Body becomes dry and leathery.

Putrefaction:

• Body wet/moist after death -- ideal environment for putrefactive bacteria and organisms.