Special interest

Cross eyed

Disclaimer: This blog is for educational purposes and please be warned that this blog contains pictures from real animal post mortems and graphic descriptions of disease.

Did you know that eyes just are outgrowths of the brain? They develop from cups of cells sitting on the forebrain. Most of the eye acts like a camera by focusing light onto the retina – the light sensitive layer of brain cells at the back of the eye. Signals from the retina travel up the optic nerve, which leaves the back of the eye and goes to the brain. If there is a problem with vision, we can work out where the damage is, by knowing the pathway the signals take. What’s interesting is that the optic nerves meet and ‘cross over’, to the opposite side of the brain.

The white X is the optic chiasm, where optic nerves from the eyes (right side of pic) 'cross over' to the opposite side of the brain.

The white X is the optic chiasm, where optic nerves from the eyes (right side of pic) ‘cross over’ to the opposite side of the brain.

The percentage of nerve fibres within each optic nerve that cross over depends on the species. In most fish, amphibians, reptiles and birds, 100% of fibres cross over, meaning that all vision from the left eye is processed by the right side of the brain and vice-versa. In other animals, there is a more even split of crossed and uncrossed nerve fibres so that each side of the brain receives signals from both eyes. This allows images from both eyes to be combined, giving us creatures with forward-facing eyes stereoscopic 3D vision with better depth perception.

There is even an animal that starts out with the nerves completely crossed, but later on ends up with split crossed and uncrossed nerves…

Advertisements
Standard
What's this?

The story beneath those teeth

There were lots of very good guesses for the brainteaser posted at the beginning of the week – no doubt some of you already got it!

The answer is enamel and dentine hypoplasia in a rabbit, in this case due to a chronic malnutrition.

right lateral view

That horizontal segmentation of the enamel and dentine happens when the metabolism of calcium and phosphate (the building blocks of the dental hard tissues, as well as bone) is disrupted. Rabbits’ teeth grow continuously throughout their lives, but the enamel is fully formed by the time the teeth erupt from the gums. Since this poor guy’s incisors are distorted along their whole length, something must have been going on for a while.

OLYMPUS DIGITAL CAMERA

On x-ray, you can see the ridges go all the way down the teeth – into the jaw bone

In this case, we weren’t entirely sure of the cause of death in this rabbit. There were many of the typical signs of starvation, like no fat stores under the skin or around organs and muscle wastage. But there was also food in the intestines, indicating that he had eaten recently (rabbits need to eat fairly continuously to keep their guts moving). It was the unusual appearance of this rabbit’s teeth that was the clincher in this case.

combo

Normal vs. segmental hypoplasia

Standard
Cases

Following all the interest in the Snow Leopard case, I’ve added a few more pictures. Here is the skull; unfortunately the delicate turbinate bones inside the nose didn’t survive the cleaning process.

Click on the pictures to see the true size of those gnashers!
DSC_0104

The skull of the snow leopard

DSC_0102

DSC_0101

DSC_0100

More snow leopard pictures!

Aside
Cases

There’s no leopard like a snow leopard

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.

I thought I’d start this blog with one of my more memorable encounters. Working in a pathology service, all our cases tend to be a combination of saddening and interesting, but this one was particularly so. A phone call had come in that morning, asking whether I would be happy to post mortem a snow leopard that had died unexpectedly. It was an exciting prospect (without a doubt the most exotic creature I’ve ever seen), but heart-breaking too; that the world has lost one of its 7500 only snow leopards.

My students had no idea what was on its way. Word spreads fast around the university and I was hoping to avoid a large crowd in the PM hall, so that my students could appreciate this beautiful animal up close in what might be the only time in their careers.

The leopard arrived in the early afternoon, with the curator of the centre where he had lived. The curator was also his keeper and a lovely gentle guy, very understandably upset by the sudden turn of events. Listening to the leopard’s history, you could see why. The previous day, like every day for the past five years, he’d been the picture of health: lively, jumping from platforms, with a strong carnivorous appetite. At midnight, keeper and leopard had their usual nightly rituals: secure enclosure, enough water, and access to shelter (not that English winter nights much compare to the leopard’s ancestral Himalayan conditions!).

So unfortunate to lose this creature, the snow leopard is magnificent even in death

The next morning the leopard was on a platform, lying dead on his front only a few hours after being checked.

On the PM table, he was as handsome as he’d ever been. There was no sign of injury, and only a tiny red dribble from the nostrils and mouth hinted that the leopard wasn’t just asleep (a scary thought when you’re looking into that mouth!).

It is common for a small amount of red fluid to be seen from the nose or mouth when an animal dies.

It is common for a small amount of red fluid to be seen from the nose or mouth when an animal dies.

Under the skin, he had no bruising that might have been hidden by the fur, and a healthy layer of fat showed he was eating enough. The abdominal organs were nicely swaddled in fat, too, and there were big chunks of meat in stomach and intestines. Whatever had felled the big guy hadn’t slowed his appetite, which is often the first thing to go if an animal feels ill. There were some tapeworms too. This isn’t unusual, but I took some worms, pieces of meat, and gut samples to test for signs of damage or poisoning. Poisoning was very low down on the list of likely causes, but you only have one chance to take some of these samples.

Air hissed into the chest as I cut through the diaphragm – the large sheet of muscle used to breathe. You use this negative pressure to suck air into your lungs, so this was another normal sign. The negative pressure can be lost for a number of reasons; if a lung is punctured (by a broken rib after a fall, maybe), a stab to the chest, or a burst trachea (wind-pipe) or oesophagus (food-pipe). It can also happen after death, if the organs have started to decay and bloat the chest.

The tongue, trachea, oesophagus, lungs, and heart are all taken out in one go, as the ‘pluck’ (or ‘haggis’ if you’re Scottish!). The red fluid leaking out of the leopard’s nose was also seen inside his trachea and airways. The lungs, too, were a dark red colour. This leopard had always lived in England, but because they originally evolved to live at high altitudes, lung problems are sometimes seen. The heart was a normal size, but one of its chambers – the right ventricle – was slightly enlarged.

Congestion.  The lungs, pictured here, and liver oozed dark red fluid from the cut surface.

Congestion. The lungs, pictured here, and liver oozed dark red fluid from the cut surface.

The only other abnormality was very subtle; the liver oozed a darkish, almost blood-like fluid when cut. It seemed a bit congested; backed-up with blood from the rest of the circulation. Sometimes this makes the edges fat and round rather than sharply tapered (as is normal), and the liver overall can feel heavier.

So far, the likely cause of death seemed to be pneumonia or some sort of problem involving the heart or circulation, but none of the post mortem findings particularly stood out. Virology had turned up negative results.

Under the microscope, tiny crystals were visible in the heart and kidneys and briefly, heartbreakingly, poisoning seemed to be a possibility. Sometimes, meat from large animals such as cows which have been euthanised (humanely killed, usually due to injury or illness) is donated to institutions keeping large carnivores. The crystals looked like those seen in animals that have been injected with barbiturate, a chemical used by vets to painlessly euthanise animals. As we know from the horse meat debacle in the UK, it is not impossible for meat of unknown origin to get mixed up in the food chain. Had this snow leopard been accidentally fed a barbiturate-laden meal? Happily, this turned out not to be the case. Meat from the leopard’s stomach tested clean and so did barbiturate toxicity tests.

It is difficult to listen to the heart of large carnivores regularly, sedation or anaesthesia is necessary.

It is difficult to listen to the heart of large carnivores regularly – sedation or anaesthesia is necessary.

In the end, it all came down to a few cells. Looking under the microscope at his heart, the snow leopard had some areas with fewer heart cells. Heart cells conduct an electrical current over the heart in a very specific pattern, making sure the heart muscle contracts in the right way to pump blood properly around the body. If there are patches of missing cells, the electrical path gets disrupted and the heart may no longer pump in its usual, regular way. That’s what seems to have happened here. The leopard likely had an arrhythmia – an irregular heart rhythm – because occasionally his missing cells made his heart contract differently for a few beats. This snow leopard seems to have had a particular type of bad arrhythmia, stopping the heart from pumping properly, and causing blood to back up in organs around the body (like the lungs and liver). Unfortunately, this type of heart damage (the cause of which is unknown) can be present in animals for many years before an arrhythmia develops or is fatal, so there was little the keeper could have done to have prevented the death of this striking animal.

Large empty spaces (containing fat) where heart muscle cells should be.

Large empty spaces (containing fat) where heart muscle cells should be. (x100, Masson’s Trichrome)

The heart of the problem.

The heart of the problem.

Standard
Uncategorized

The new Veterinary Forensics blog!

Welcome to the new Veterinary Forensics blog!  I hope to post regularly on all matters of Veterinary Forensic pathology and associated fields.

The field of veterinary forensics is relatively new and, as such, must draw data from the human field of forensic medicine. Few resources exist for the veterinary forensic pathologist and I hope the field will continue to grow and have an impact on improving animal and human welfare.

But what is the role of the veterinary pathologist in forensics?

Animal cruelty cases are, sadly, very common. Post mortem examinations and microscopic examination of tissues are often the only proof of abuse, neglect and, equally important, disproving these allegations. Likewise, wildlife crime is investigated, in part, by veterinary pathologists. Insurance claims, inquests, malpractice cases and crimes in which animals are involved, are some of the other scenarios in which the experience of veterinary pathologists is employed to build a case for defence or prosecution.

Hopefully this blog will offer an insight into this fascinating field for those interested in veterinary forensics, provide an introduction to those training in the field and a stepping stone for further information. Enjoy!

Standard