Forensic Pathology

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