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.


A wonderful bird is the pelican, his bill will hold more than his belican

A wonderful bird is the pelican,
His bill will hold more than his belican,
He can take in his beak
Enough food for a week
But I’m damned if I see how the helican
Dixon Lanier Merritt (1879–1972)


This handsome chap had to be put to sleep after a wound failed to heal on his abdomen.  Dixon was correct in his limerick; we found his beak was 10 litres in volume, compared to the one litre volume of his stomach.

His abdominal wound was too large to close with stitches, so a dressing was used to see if the wound would contract by itself.  Unfortunately it appears the skin became infected, so it was decided euthanasia was the kindest thing to do in his case.

The wound on his abdomen was infected and failed to heal, despite attempts to treat the infection

The wound on his abdomen was infected and failed to heal, despite attempts to treat the infection


Contagious Cancer; Transmissible Venereal Tumour (TVT)

Cancer and infectious diseases frequently appear in the news.  This is probably because they scare us, with headlines featuring news of outbreaks of infectious diseases, or suspected causes of cancer.  Similarly, there is much interest in developments of better methods of diagnosis, treatment, prevention and eradication.

But imagine if there was a cancer which was infectious.  We’re not talking about viruses or bacteria which may lead to the development of tumours (like human papilloma virus in cervical cancer, and helicobacter in stomach cancer).  But if the tumour cells themselves were contagious…

Unfortunately there are four known types of transmissible tumour in animals.  Transmissible venereal tumour (TVT) in dogs is the feature of this blog post.  The others are a tumour of Tasmanian devils (Devil facial tumour disease), a tumour of Syrian hamsters spread by mosquito bites, and a form of leukaemia in soft-shelled clams.

We recently had a case of suspected TVT in a dog.  The dog presented with a mass on it’s penis, from which a smear was made and examined (cytology).  The mass was removed and slides prepared for microscopic examination (histopathology) which confirmed that it was TVT.

TVT cytology x400

Microscopic appearance of TVT

Microscopic appearance of TVT

It is thought that the tumour cells originate from a type of cell called a histiocyte.  One of the reasons we know these tumours don’t arise from the dog’s own cells is that the tumour cells have fewer chromosomes (less than the 78 normally in a dog), and the chromosomes have a different appearance to dog chromosomes.  It has also been shown experimentally that the tumour can be transmitted from one dog to another, and even to other canine species, such as foxes.

The tumour spreads between animals during copulation, licking, biting or other contact with infected animals.  The tumour may spontaneously regress, if a sufficient immune response occurs, or the animal can be treated with surgery, chemotherapy and/or radiotherapy.


Super stretch!

The ability of skin to maintain it’s shape and integrity is due to collagen arranged in regular bundles within the dermis.  If these bundles are malformed and arranged in irregular patterns it can result in the skin being super stretchy!

collagen dysplasiaThis condition is called collagen dysplasia, the downside is that the skin is much weaker than usual too, so tears easily.

This image is from the fantastic textbook ‘Pathologic Basis of Veterinary Disease’



The title might give you one eye-dea about today’s topic – yup, we’re talking about cyclopia! Our fun-loving, larger-than-life, mono-ophthalmic monster buddies were first written about by the ancient Greeks, and later adopted by the Romans.

Luckily he has really bad depth perception

Lucky for those guys, he has really bad depth perception

The origins of the cyclops myth has been the subject of much discussion. Some suggest that the Greeks might have stumbled across the fossilised skulls of prehistoric dwarf elephants, and these creatures being extinct and unfamiliar to them, mistaken the schnozz-socket for a single giant eye.

Nasal cavity vs. actual eye hole

Nasal cavity vs. actual eye hole of an elephant skull

Others think that the Greeks had actually seen cyclopes in the flesh. A couple of rare developmental problems can result only one eye: in true cyclopia, only one eye is formed, whereas in synophtalmia, there may be two eyes which fuse.


Itty bitty cyclops kitty

The Sonic Hedgehog and Pax6 genes are involved in properly dividing the embryonic brain (and extensions from it, such as the eyes) into two separate hemispheres.  There are several things that interfere with this process and so cause cyclopia, including certain drugs, viruses, genetic defects, and radiation. Alkaloid toxins in plants are also a culprit. In fact, ancient Greeks used some of these plants medicinally, and perhaps as a result, did see ‘real’ cyclopes…

Elephants and cyclopes also have another thing in common. Interestingly (or maybe morbidly), some cyclopes develop a tube-like structure instead of a nose, which is called a proboscis because it resembles a tiny trunk.

A cyclopic lamb with a proboscis, or trunk, above its eye

A cyclopic lamb with a proboscis, or trunk, above its eye



Extra toes!

Are cats evolving opposable thumbs??? (More pictures here)

Cat with opposable thumbs!?

Cat with opposable thumbs!?

Probably not.  Polydactyly is a condition where extra fingers and/or toes develop in animals.  Sometimes they are fully formed, sometimes they just form a small under-developed finger-like lump.  Usually there is a genetic defect that causes the extra digits, but it has been associated with the mother taking some types of medications at particular points during pregnancy.

Extra fingers and toes with near-normal anatomy in a human.

Extra fingers and toes with near-normal anatomy in a human.

220px-Polydactyly_01_Lfoot_APPolydactyly can occur in many species, and is sometimes associated with other abnormalities such as limb deformities and heart problems.  It may cause no problem at all, and can assist with mental arithmetic.

Polydactyly in a chicken.

Polydactyly in a chicken.


Cases, What's this?

What’s this? #5 Amyloidosis

Last week we asked “what’s this?”. Alicia D got it right with renal glomerular amyloidosis, and paleomanuel also correctly spotted some swelling! To understand what’s going wrong in this kidney, we first need to understand the problem with proteins.

When proteins go wrong, all sorts of chaos can occur in the body. One particularly interesting abnormality is when the proteins fold incorrectly when being made, and stick together in clumpy plaques (called proteinopathies = protein + pathology).

You are nothing without your proteins. They act out the instructions written in your DNA – making and holding us together (connective proteins), allowing us to grow and move (contractile and cell division proteins), giving us energy (metabolic and oxygen transport proteins), defending us (immune proteins), giving us colour (pigmentary proteins), and so on and so on and so on!

File:Main protein structure levels en.svg

All proteins are built up from long chains of smaller molecules called ‘amino acids’ (a protein’s primary structure; the lego blocks of life).  These chains fold into different shapes (secondary structure).  Sometimes these fold further – tertiary structure.  And some proteins are made up of multiple folded chains – quaternary structure (super complicated lego mansion).

The accummulation of protein gives the kidney a yellow colour

The accummulation of protein gives the kidney a yellow colour

‘Amyloidosis’ is actually a group of diseases caused by a build up of sticky protein plaques.  Some types of amyloidosis are inherited, like ‘Shar-Pei Fever’ (not to be confused with Sharpie Fever) in Shar-Pei dogs.

Shar-pei dogs, which can actually become airborne in strong winds

Shar-pei dogs can actually use their skin folds to become airborne in strong winds…maybe

In affected dogs, the liver over-produces a protein called serum amyloid A (SAA) involved in inflammation. Some of the SAA proteins fold incorrectly, making sheets that stick together.

Congo red (x100) stains the amyloid fibrils orange-red within the glomeruli

Congo red (x100) stains the amyloid fibrils orange-red within the glomeruli

The sticky sheets of protein float around in the blood, and get lodged in the kidney’s blood filtering machinery (the glomerulus). They stick together and clog up the filter, making the kidneys appear swollen and discoloured with proteinaceous gunk. The delicate blood vessels in the glomerulus are a bit like coffee filter paper: they are easily torn and damaged by trying to push past the protein clogs and keep filtering the blood clean. Once damaged, normal molecules are lost rather than filtered (like coffee granules leaking past the filter paper in to your cup). Once the kidneys lose their ability to filter, we call it kidney failure. Because the whole thing is triggered by repeated episodes of inflammation and SAA release, it is often associated with fever in Shar-pei dogs.

Iodine stains the amyloid deposits in the glomeruli black

Iodine staining the amyloid deposits in the glomeruli dark brown

Amyloid reacts with iodine and forms big brown blobs, so we can see the clumpy SAA plaques in the kidney with the naked eye. We can also stain it with Congo Red under the microscope, which stains the proteins red.  In fact, the Congo Red dye binds in a very regular pattern, almost crystal like, so that when polarised light is shone through it, it becomes apple green…

Polarised light reveals the Congo Red dye as apple green, when bound to amyloid fibrils

Polarised light reveals the Congo Red dye as apple green, when bound to amyloid fibrils