What's this?

What’s this? #12 Renal infarcts

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.

renal infarctions

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.



Coccidia vs. Macrophage

Enteric coccidiosis, the infestation of the small intestine by the Eimeria spp. parasites, is a common cause of diarrhoea and even death in rabbits.


Autolysed villus with a macrogametocyte (H&E x400)


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.


Giant cell (arrow) engulfing an oocyst


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.

What's this?

What’s this? #11

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!

Foal lung with arrows