Answer to follow later this week!
Answer to follow later this week!
Infarction is death of tissue because the supply of oxygen is cut off. Typically this occurs because a blood vessel is blocked. Causes of blockages include thrombi (clots), bacterial emboli (bits of abscess that break off into the bloodstream), and tumour emboli (bits of tumour which break off into the bloodstream).
Because more than one vessel might supply a tissue an infarction will only occur if i) all the vessels are blocked at once, or ii) the area is supplied by a single artery (also called an ‘end arterial supply’). One organ predisposed to infarction due to having an end arterial supply is the kidney.
At post mortem examination a recent (acute) infarction will be visible as a really well demarcated zone of reddening. This reddening corresponds with the area supplied by the blocked vessel(s).
Over time, the dead tissue is replaced by fibrous tissue (scar tissue) which contracts downwards to leave an indentation.
This kidney has an acute infarction; the dark red wedge on the cranial (top) pole of the kidney. And a more longstanding (chronic) infarction; the indentation on the caudal (bottom) pole of the kidney, where you can see the remnants of the dark red discolouration.
Can you guess what this is? Tissue from a dog. Answer to follow later this week!
Enteric coccidiosis, the infestation of the small intestine by the Eimeria spp. parasites, is a common cause of diarrhoea and even death in rabbits.
There are loads of species of Eimeria. If they cause disease they shrink the villi (finger-like projections in the intestine) by destroying the enterocytes (cells that line the villi). This leads to poor absorption from the gut lumen, and also leakage of fluid into the lumen. This results in diarrhoea. Dehydration and electrolyte loss can prove fatal to the rabbit.
The immune system tries to get rid of the parasite. Below we managed to capture the moment a team of macrophages have fused to form a giant cell, which is in the process of ingesting (by phagocytosis) a parasite oocyst.
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.
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).
Skull fractures can be classified as:
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.
Last week we asked you to identify the pigment (orange arrows) and elliptical material (black arrows) in this image.
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.
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.
Here is a picture from the lungs of a foal (H&E, x400). The alveolar capillaries are distended by red blood cells (congestion). Do you know what the granular pigment (orange arrows) and elliptical material (black arrows) are? The answer will be revealed early next week!