Forensic pathology regards the diagnosis of when a lesion occurred and how it occurred. All physicians will have to deal with violence and trauma at
some point. It is important you can describe a lesion well and accurately as your report may be used as evidence in a court case. You should be able to diagnose a lesion, age it, describe it and know
what to do to preserve evidence.
There is a branch called humanitarian forensic medicine, for
example proving migrants underwent torture in their home country. For these migrants, the evidence
you present may determine whether they will be allowed political
exile or not. Your report is the only piece of paper that will be able to support the evidence
of ill treatment or torture when presented to regional councils and police.
In humanitarian forensic medicine you may also be needed to age unaccompanied minors of undetermined age. For example migrants
without any documents, is the migrant above 18 years age? it could make
all the difference. Police can refuse territory to migrants over 18yrs. You need
to know what to do to verify age.
Forensic pathology starts with a physical exam. You need to
assess the whole body (you also need to listen to the patient, don’t forget!).
If you don’t document a lesion or ‘crime’ and the victim doesn’t talk, then any
evidence of the ‘crime’ will disappear. No sign of a crime can remain if there
is no documentation. You need to have a keen eye to spot scars or bruises on
darker skin.
Description of lesions needs to be metric and repeatable, there
is no reason to not take a photo of a difficult to describe lesion. (although
now there are issues with tampering of photos with programmes such as
photoshop). If you take a picture, place a ruler in the periphery of the lesion
at the same level of the lesion and consider putting a coin in the photo to
help spot distortion or modification of the image later. Lastly make sure you
take the picture perpendicular to the skin surface.
How do you describe a lesion?
Need to address:
- area of body affected
- type of lesion
- colour
- edges/limits
- shape
- orientation
- size
Types of lesions:
Blunt force trauma
Sharp force trauma
Gun shot wounds
Asphyxia
Thermal injuries
Poisoning
Blunt force trauma
- Excoriations
- Bruising
- Lacerations
Cause by any force against the body surface by a blunt
object. You can tell on a cadaver if the blunt force was performed when the
cadaver was alive or dead by looking at histology. On histology, live tissue injury
will show an inflammatory reaction with extravasation of red blood cells into
the tissue. On dead tissue there is no inflammatory reaction, you can also use
immunohistochemistry to spot the presence of cytokines and see if there are
inflammatory cells present.
Excoriations
Excoriations are loss of the superficial layers of skin due to blunt force
trauma (not an abrasion, an abrasion is loss of the superficial layers of the
skin caused by an object with a sharp margin like a knife). Excoriations often
reproduce the shape of the object that cause it.
Often the excoriation will
heal with a scab and at this point it will become impossible to age the lesion.
ED physicians may be the only people able to preserve material evidence of
assault from the lesion. It’s easy, you simply swab the lesion for 30 seconds
before cleaning the lesion (moisten the
swab with sterile water or saline before), store the swab in a tamper proof
container and dry or freeze it (you can later give it to the police if
necessary). Often under the nails of victim there is often attacker DNA (there
can even be attacker DNA on the surface of a bruise from punches etc).
With excoriations you can often tell in which direction the
blunt injury was caused and this can help reconstruct the event. (yet another
reason for a good description and often there is some material left on the
lesion from whatever object was used to create the lesion).
Scratch marks are a very typical and specific form of
excoriation. Triangular or droplike in shape. They contain a lot of information
about the author of the lesion and genetic information. A tyre mark may be another
kind of distinct lesion (often the actual lesion is caused by the negative
pressure by the treads in the tyre not the actual tyre surface).
Bruising
A bruise means the trauma was in that place, a hematoma is a collection of blood and the trauma causing the hematoma may be elsewhere on the body. When in doubt it is best to describe the lesion as a cutaneous discoloration.
Great example; black eye can be caused by a direct trauma (punch to the face) forming a BRUISE or may be caused by a basilar fracture of the cranium creating the so called racoon eyes this is a HEMATOMA. They will look almost identical.
Note that MRI can be used to age and discover origin of a bruise/hematoma. Not that bruising may be difficult to spot for example of North African darker skin.
A bruise is different to a hematoma!
Bruises are closed lesions that show a distinct
discoloration. The colour relates to the age of the lesion but also the size is
important. You may have different colours at the edge compared to the centre of the lesion due to difference in
breakdown. You need to assess them carefully. For example a patient with multiple small
bruises of same colour you can hypothesise were all caused at the same
time. One large bruise may be purple while a neighbouring small bruise caused
at the same time may be yellow.
Colour therefore depends on physiology, depth of injury and
size.
Remember not to confuse a bruise with a hematoma.
Hematoma = filling of blood into a virtual space
Bruise = forcing of blood into a tissue
Note that old people bruise very easily and may even bruise
spontaneously.
Lacerations
Third kind of blunt injury is a laceration. A laceration is
simply a discontinuation of the skin, you can put the two skin edges together
as normal and reconstruct the skin as there is no loss of substance. Bear in
mind that a skin discontinuation may also be cause by a sharp force trauma. You
have to describe the margins well. Big
clues that the laceration was caused by a blunt force trauma is irregular skin
edges or frayed edges and bridges of tissue. You can look at the subcutaneous tissue
and it will be irregular and not smooth with a blunt force trauma.
Sharp force trauma
- Penetrating injury
- Cut marks
- Stab wounds and mixed injuries
Penetrating injury
Depending on the book you use, pointed objects may or not be
included in this category. A very distinct lesion to look for is needle tracks
or syringe wounds. Always look for syringe marks in any unconscious patient, observe
the whole skin surface, needles may be injected behind the ear or even on the
genitals.
The shape of penetrating object lesions can tell you the
shape of the object tip used to cause the lesion. The flaps of the skin lesions
will match the penetrating object tip for example a squared end will cause an X
shaped flap, a triangular tip will cause a Mercedes sign skin flap and a
circular point a circular lesion.
An example is a penetrating injury to the cranium, surgeons
keep the piece of cranial bone with the penetrating injury, the shape of the
hole in the bone can tell you what kind of object caused the injury.
Cut marks
Cut marks are caused by a sharp edge weapon and cause a neat
discontinuation of the skin edge and tissue. The cut mark usually has a tail at
the edge of the skin discontinuation and this can give you a lot of information
about where pressure was least and hence in what direction the cut was performed
(obviously this depends on the curvature of the skin area and the object used,
its still difficult to tell entry and exit point).
Stab wounds
Mixed weapons can give you stab wounds. These are weapons that can stab and can also cut. The cut mark is the result of passing the sharp edge and
the penetrating injury the result of the pointed edge. Stab wounds contain a
lot of information and will often reproduce the cross section of the blade. For
example a double edged blade will produce a wound with two acute ends, a single
edged blade will produce a wound with a single acute angled corner and an
obtuse angled corner. Sometimes the
going in wound will not match well the going out wound and stab wounds may
crossover each other making the lesion more complex and difficult to describe.
Remember that on skin and bones you may have residues of the
instruments used to cause the lesions and you should always keep any debrided
material.
Gun shot wounds (GSWs)
See future post on gun shot wounds...
Asphyxia
Asphyxia is a manner of death or disease that has distinct signs
left depending on the method of asphyxia, the main types of asphyxia are:
- Smothering
- Choking
- Manual strangulation
- Ligature strangulation
- Hanging
- Drowning
- Traumatic (compression) asphyxia
- Plastic bag suffication
Unfortunately due to frequency of plastic bag suffocations in
forensic pathology it has managed to deserve its own type of asphyxia.
With asphyxia there are many different types lesions that
can be seen on the cadaver such as liver mortis, early rigor, delayed cooling
etc. however, only one type of lesion is found on living bodies, petechiae!
Petechiae
is a very distinct sign of asphyxia and is caused by high pressure in the capillaries
causing them to burst. Not always seen, it can be subtle, for example on the
conjunctiva it is a common sign with strangulation.
Smothering is a good way to get away with murder there is
often no sign apart from petechiae. There may be scratch marks, compression
marks from teeth inside the lips or fibres from the object (usually a pillow).
Choking is usually accidental often people with neurologic
or psychiatric disease or issues with the swallowing reflex.
Strangulation is a mechanism of death and not necessarily the
lack of air. The death can be caused by nervous factors such as compression of
the glomus body of the carotid artery and reflexive cardiac arrest. There are
many anecdotal deaths where an aggressive attacker grabs an old man by the neck
and he just drops dead almost instantly (the attacker will be mentioning in
court how he hardly touched him). You usually see bruising with compression of
the airways. Fracture of the hyoid or cricothyroid cartilage can have a
distinct pattern with strangulation too. A ligature strangulation will often
have a linear bruise of uniform depth sometimes with fibres still around the
area (eg. rope burn).
With hanging there are often distinct fractures and ligature
signs. You can tell easily if the person was hung before or after death by
again looking at the haemorrhaging in the neck and the presence of an
inflammatory response which is lacking with a dead body.
Traumatic asphyxia is caused by a heavy object compressing the
rib cage restricting breathing.
Drowning is an awful way to die, often taking longer than 6
minutes as you alternate between periods of consciousness and unconsciousness. An
important note is that water in the lungs is not proof of drowning! There is
often water in the lungs in cadavers and it may have many origins (although
sometimes it can be obvious with the post autopsy lung able to stand by itself it’s
so full of water). Often the only proof of drowning is the presence of diatoms
(microscopic algae) in the blood and organs (the diatoms being distinct to the
body of water where the drowning occurred). When you drown the alveoli burst
and water mixes with the blood providing an entry point for diatoms to enter
the blood. A long period after drowning
there may be characteristic skin wrinkling and pink discoloration but this is
more for shipwreck victims for example.
Thermal injuries, a common form of abuse. (see post on
burns)
Poisoning
History is so important! Diagnosis of poisoning will
require; anecdotal evidence, autopsy and clinical toxicology. If suspected keep
a sample of blood/urine for a specific toxicology test that may be needed
later. Many poisons are not included in the general toxicology screen performed
in most ER’s. Also consider keeping a small lock of hair (from the roots), with
this you can prove that the drug was not present in the victims system at time
zero.
There were far too many gruesome images that were associated to this post so here is a raccoon reacting to them
