Fatal fractures

Head and spinal injuries are important topics in forensic pathology because (maybe obviously) they are often seen in fatal cases: the same trauma applied to another body part is often much less serious, and these areas are prime targets in deliberate attacks.

Skull fractures

It may not seem like it, but all bone is slightly elastic – it can bend a little before it breaks. When you receive a blow to the head, your skull deforms momentarily: bone bends in at the impact site (intrusion) and bulges out around it (extrusion). If the blow is forceful, it may exceed the bone’s elastic limit. The bone can no longer bend, and instead it breaks. It may not necessarily break at the exact site of impact! When a bone bends, one side is compressed and the other side is under traction.


The structure of bone means that it is strongest under compression, compared to traction. When it bulges, the outer surface of the bone is stretched and can fracture away from them impact site.

Fracture lines won’t cross preexisting fractures, meaning you can tell which impact came first (known as Puppe’s rule).


Puppe’s Rule (From: Intersecting fractures of the skull and gunshot wounds. Case report and literature review. Guido Viel, Axel Gehl, Jan P. Sperhake. Forensic Science, Medicine, and Pathology, March 2009, Volume 5, Issue 1, pp 22-27

Skull fractures can be classified as:

  • Linear fractures
    • Straight or curved fracture lines (most common)
    • Hinge fractures are linear fractures along the base of the skull.  The horse below reared-up, fell over backwards and landed on its head.  It died instantly.
    • Diastases are separations of the skull bones along their sutures (joints with adjacent skull bones)

Hinge fracture at the base of a horse skull

  • Ring fracture
    • Around the opening of the back of the skull (foramen magnum), where the spinal cord meets the brainstem, when forces are transmitted along the spine to the head e.g. fall from a height.
  • Depressed fractures
    • Bone or bone fragments are pushed into the skull cavity
  • Pond fractures
    • Depressed fractures which leave a concave pond-like cavity

Healed pond fracture

  • Mosaic (also called Spider’s web) fractures
    • Linear fractures which radiate from a depressed fracture

Space inside your head is at a premium, which is why skull fractures are so life-threatening. Anything taking up extra space (like bone bending inward) squashes the brain. Fractures can rip through nearby vessels, and bleeding in the head takes up limited space. The brain also risks injury from loose shards of bone. Finally, the battered brain may swell (oedema) under all this abuse and compromise its space and blood supply further.

What's this?

What’s this? #11 Foetal aspiration

Last week we asked you to identify the pigment (orange arrows) and elliptical material (black arrows) in this image.

Foal lung with arrows

This tissue is from a foal which was born dead.  The pigment is meconium – the faeces passed by a foetus when it is in the uterus.  The elliptical material are scrolled skin cells, called squames, which are shed by the foetus during pregnancy.  They are refractile, as can be seen in the next image of the same area of lung using polarised light.

polarised squames

The pink feathery material is protein rich fluid (amniotic fluid).  These findings are consistent with aspiration of amniotic fluid by the foal because of distress, drawing meconium, dead skin cells and aminiotic fluid deep into the lungs as it gasps.  This might be due to a twisted umbilical cord, for example.


The long lens of the law

We already use microbiology routinely in forensic pathology for identifying potential organisms which could be causing a disease or infecting a wound.  However work in recent years looks like it might be adding some more roles for the microbiologist in forensic investigations.

Bacteria are grown in labs to allow identification of the species.

Bacteria are grown in labs to allow identification of the species (Image from Wikimedia)

Forensic microbiology is an exciting area of research at the moment, including uses in forensic identification, tracking the interaction of people with their environment, and even deducing time since death in cadavers.

The bacteria which live on healthy individuals is called the human microbiome, and is similar between all humans.  However, it is the differences between individuals which has attracted the attention of some pioneering microbiologists.  The Human Microbiome Project is attempting to answer some basic questions about our microbiome (Blaser 2010):

  1. Which species of microbe inhabit humans?
  2. What are the microbes doing?
  3. How is the immune system responding to these microbes?
  4. What are the forces maintaining the balance between microbe and human?
  5. What are the unique characteristics between humans?

A group from Washington University School of Medicine (Fierer et al 2010) has shown that you can identify individuals based on the unique population of bacteria inhabiting their skin.  Not only that, but you can compare the population on their skin to the population on an inanimate object, such as your computer keyboard and mouse to identify who used it!

E coli

E coli (Image from Wikimedia)

Another group has shown that cell phones share the microbiome of their human owners (Meadow et al 2014) and Simon Lax (2014 and 2015) has shown you can link the bacterial population on people’s shoes  and the floor to work out where people have been…

Particularly exciting to pathologists is the potential to use the change in bacterial population on a dead body over time to estimate the time since death.  More work is required in this area, but the results from Jessica Metcalf at the University of Colorado at Boulder looking at mice are promising.

Of course, there are limitations to these applications which need more work, such as the effect of antibiotics and cleaning products which may be present in the person, cadaver or environment which could confuse results.

References and further reading:

Blaser MJ. Harnessing the power of the human microbiome. PNAS 2010;107:6125-6126.

Fierer N, Lauber CL, Zhou N, McDonald D, Costello EK, and Knight R. Forensic identification using skin bacterial communities. PNAS 2010;107:6477-6481.

Metcalf JL, Parfrey LW, Gonzalez A, et al. A microbial clock provides an accurate estimate of the postmortem interval in a mouse model system. eLife 2013;2:e01104.

Meadow JF, Altrichter AE, and Green JL. Mobile phones carry the personal microbiome of their owners. PeerJ 2014;2:e447.

Lax S, Smith DP, Hampton-Marcell J, et al. Longitudinal analysis of microbial interaction between humans and the indoor environment. Science 2014;345:1048-1052.

Lax S, Hampton-Marcell JT, Gibbons SM, et al. Forensic analysis of the microbiome of phones and shoes. Microbiome 2015;3:21.


Special interest


A day in the life of a Veterinary Forensic Pathologist!

Everything I think of is already a thing


Exactly what Veterinary Forensic Pathology is like.

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Bloody cancer…

Disclaimer: This blog is for educational purposes and the cases described are not from any one animal. Please be warned that this blog contains pictures from real animal post mortems and graphic descriptions of disease.

Chief bounded into the house after returning from his evening run around the park – he knew dinner would be ready for him!  Half way across the hall, a couple of metres from his food bowl, he collapsed on the floor.  He seemed unconscious, and his owner dropped the can of food she was opening to rush over.  Lucky for Chief, his owner was a vet.  She tried to keep a cool head as she checked him over. His pulse was fast but weak and his gums were very pale; he was starting to regain consciousness but was too weak to stand up; his breathing was fast and ragged; he didn’t react to his name — these were all signs of shock from blood loss.  She carried Chief to the car and sped to the veterinary surgery.  His owner already realised that he must be anaemic or bleeding internally. There had been no sign of anything amiss with Chief, and he was checked often at home (no doubt far too often if you asked him!). Even so, at the back of her mind, Chief’s owner knew what could be wrong.

She’d called ahead to colleagues at the practice, and the scene when they arrived was like something out of an ER episode.  However, despite their best efforts, Chief passed away.  Resuscitation was attempted, but unsuccessful.  Distraught, Chief’s owner brought him to us for a post mortem to check whether her suspicions has been correct.

The abdominal cavity was full of blood.

The abdominal cavity was full of blood.

Inside the abdomen, the cause of Chief’s sudden collapse was immediately obvious.  Litres of blood filled the space around his abdominal organs.  As his owner had thought, he’d bled internally.  Our job was to find out from where, and why.

White arrows: malformed blood vessels in a haemangiosarcoma (x40 H&E)

White arrows: malformed blood vessels in a haemangiosarcoma (x40 H&E)

One by one the organs and their attachments were checked, before removing them for more thorough examination.  From what we knew already and after finding a blood-filled abdomen (haemoabdomen), top on my list was a haemangiosarcoma.  This is what Chief’s vet thought, too.

The word ‘haemangiosarcoma’ can be broken down.  ‘Haem’ = blood, ‘angio’ = vessels, and ‘sarcoma’ = a category of tumour, so altogether haemangiosarcoma = a tumour of blood vessels.  In fact, these tumours are a mish-mash of rapidly growing and badly developed bundles of blood vessels.

White arrows: malformed blood vessels in a haemangiosarcoma Black arrows: Red blood cells (x200 H&E)

White arrows: malformed blood vessels in a haemangiosarcoma
Black arrows: Red blood cells (x200 H&E)

Being cancer, the blood vessels grow uncontrollably and so are poorly formed . They are very prone to bleeding, and will often have many little bleeds all the time. These clot and heal, but will use up many of the platelets and clotting factors in the blood. Eventually there is a big bleed because all these factors essential for clotting have been exhausted. It cannot clot, and just keeps bleeding.

The spleen is the most common site of origin for this tumour. Not surprisingly, when the spleen was examined, we found a large, dark-red mass was present.

Large, dark red tumour on the spleen

Large, dark red tumour on the spleen.

Haemangiosarcomas are malignant tumours which can spread around the body by leaking tumour cells into the blood.  Some of the places they commonly spread (metastasise) to are the lungs, right atrium chamber of the heart, the brain, kidneys and liver.

Lung:  The dark red spots are multiple tumours (haemangiosarcomas) spread from the spleen to the lungs.

Lung: The dark red spots are multiple tumours (haemangiosarcomas) spread from the spleen to the lungs. Each new tumour is the result of a single cell breaking off the original cancer and traveling to a new site.

Wind pipe: Bleeding of the tumours spread to the lungs results in blood in the trachea.

Wind pipe: Bleeding from the lung tumours means we sometimes see blood in the trachea (windpipe).

These metastatic tumours, which are said to have ‘seeded’ elsewhere, also bleed.

Haemangiosarcomas can originate from other sites apart from the spleen, including the heart, bladder and skin.  If they originate or spread to the heart, blood can fill the sac which surrounds the heart (the pericardial sac).  Blood in the pericardial sac squeezes the heart from the outside and prevents it from filling properly. This is called cardiac tamponade, and means when the heart beats it has nothing to pump around the body.

The dark red area in bleeding into the pericardial sac which can result in cardiac tamponade.

The dark red area is bleeding into the pericardial sac which can result in cardiac tamponade.

The problem with haemangiosarcomas is that they can appear and then grow very suddenly, the animal may have no signs of ill health until the bleeding causes shock and collapse.  If they are detected, some can be surgically removed, although they have often spread by this time, so chemotherapy is used in some cases.  Sometimes they can be detected because they cause external signs, such as a bladder haemangiosarcoma which bleeds into the pee.

The dark red area is a haemangiosarcoma from the wall of the bladder.

The dark red area is a haemangiosarcoma from the wall of the bladder.

Unfortunately, Chief’s tumour wasn’t obvious until he collapsed, and so there was little his owner could have done in this case.

What's this?

Who’s this? Wilbur the rove beetle, of course!

Last week we asked why this guy is such a big deal in pathology. Pakasuchus came very close in guessing – although Wilbur is alive and kicking, the body he lived in most certainly was not!

Wilbur and his bug buds are important to pathologists because they are the best way to figure out the time of death. The study of insects (and other arthropods) in decomposing remains is called forensic entomology. Wilbur is a rove beetle (Ocypus sp.), and eats maggots that infest dead bodies. Bugs ‘colonise’ bodies with a very particular timing and in a very specific order depending on the conditions around them, which forensic entomologists use to estimate the time since death.

The order can vary hugely, but generally the first wave of colonisation brings blow flies, attracted by the smell of blood, body waste, and general death odour, which lay their eggs on the body. These flies in turn attract further fly species (including the appetisingly-named ‘cheese flies’ and more conventional corpse flies), and along with decomposition, sets up the second wave of colonisation. The third wave, attracted by rancid fat, arrives, and now that the body is popular the more hipster members of the first wave get bored and move off.

Doesn't just eat cheese!

Doesn’t just eat cheese!

Eventually, Wilbur and his beetle buddies muscle in on the action. Some feed off the rotten juices, others tackle drying tissue (too tough for the flies), but Wilbur likes his meat fresh – other bugs are the plat du jour!

Wilbur's dinner!

Wilbur’s dinner!

Although most people are familiar with forensic entomology in human murder cases, it is also used to determine time of death in animal cruelty cases.

Bugs can also be a valuable source of other evidence too. Different creepy crawlies obviously live in different places, so can identify the geographic location of death. But they also have very specific local preferences too; some preferring sun, others shade, and even some indoors! They can tell you where the body was at the time of death, and where it has been since – useful for tracking the footprints of bad guys (and zombies).

They might tell you about the circumstances that an animal has come from. Certain flies are attracted to urine and faeces and their presence on a body suggests that the animal may have lived in a confined area surrounded by its own waste prior to death.

If the body has been in a fire, insects can survive safe inside the skull munching on grey matter,  telling you whether the animal died before or during the fire. If the latter, they will also tell you the time of the fire.

Usually different body tissues are sampled to test for the presence of drugs or poison, but if the body is too rotten or otherwise destroyed (e.g. burned), maggots can be tested instead! Having no arms or legs, maggots can’t hold on and frequently fall off the body. DNA can also be recovered from these maggots’ stomachs, to prove the body was in a certain place or in cases where it hasn’t been found.

Even no bugs at all is an entomological clue! Lack of insects on anything but a fresh corpse suggests that it has been frozen, kept in a tight container, or buried very deeply underground.

the more you know


A shot in the dark

Disclaimer: This blog is for educational purposes and cases described are not from any one animal. Please be warned that this blog contains pictures from real animal post mortems and graphic descriptions of disease.

This was a case with a couple of twists. It started with a dog whose skin felt just a little strange. He came to his vet, and it sounded as though his chest and front leg was covered in bubble-wrap, crackling when touched. This is how air trapped under the skin (tissue emphysema) feels. Tissue emphysema commonly happens after traumatic injuries, where outside air is forced through wounds under the skin, or alternatively, can escape from the lungs after chest injuries.

Bubbles of air and oedema in the subcutaneous tissues

Bubbles of air and oedema in the subcutaneous tissues

Hidden under the dog’s fur, there were indeed several shallow wounds. X-rays revealed three air rifle bullets lodged in the dog’s foreleg, ribcage, and abdomen. The vet operated and retrieved the bullet from the abdomen.

During surgery, everything seemed fairly ok. Air rifles are classed as ‘low velocity’ guns, meaning the bullets travel under a thousand feet per second (unlike high velocity bullets which travel over 2500 feet a second). The surgeon checked carefully, and it seemed that the bullet hadn’t directly entered the intestines or any organs.

The bullet hole in through the abdominal muscles, but no direct intestinal perforation....

The bullet hole in through the abdominal muscles, but no direct intestinal perforation….

But then, shortly afterwards, things took a negative turn. The dog developed a fever, rapid, unstable breathing, and dependent oedema – signs of sepsis, or blood poisoning. Unfortunately, this carries a poor prognosis and high chance of suffering, and he was euthanised on humane grounds.

Bullets cause damage by cavitation; tissues in the bullet path balloon and stretch, tear, and then finally contract. Because of this, tissue damage is not necessarily confined to the direct bullet path.

Tissue cavitation creates a negative pressure that sucks hair and contaminants into the bullet wound. In the post mortem, it became clear that damage extended far beyond the bullet’s path. It seems that even though the bullet hadn’t penetrated the intestines, it had damaged them. Faecal material leaking from the guts was combined with debris sucked into the wounds, setting up a huge infection in the abdomen, chest, and tracking under the skin. The chest, abdomen and subcutaneous layers were filled with litres of watery, red fluid – oedema and blood, a result of massive inflammation due to infection.

Lots of oedema and bleeding under the skin - look how wet those tissues are!

Lots of oedema and bleeding under the skin – look how wet those tissues are!

Sadly, as pathologists we can find out how an animal died, but in some cases we cannot fathom why.

One of the other bullets, lodged deep in a muscle

One of the other bullets, lodged deep in a muscle