Abstract
Fat embolism is the mechanical blockage of blood vessels by circulating fat particles. It is frequently related to traumas involving soft tissues and fat-containing bones. Different techniques have been used for decades to demonstrate histologically fat emboli, being the extremely toxic post-fixation with osmium tetroxide one of the most used techniques in the last decades. In the present study, the osmium tetroxide technique was compared qualitatively and quantitatively, for the first time, with chromic acid and Oil Red O frozen techniques for histological fat emboli detection in the lungs of eight sperm whales that died due to ship strikes. This was also the first time that chromic acid technique was tested in cetaceans. Results showed that the three techniques were valuable for the histological detection of fat embolism in cetaceans, even when tissues presented advanced autolysis and had been stored in formaldehyde for years. Although quantitative differences could not be established, the Oil Red O frozen technique showed the lowest quality for fat emboli staining. On the contrary, the chromic acid technique was proven to be a good alternative to osmium tetroxide due to its slightly lower toxicity, its equivalent or even superior capacity of fat emboli detection, and its significantly lower economic cost.
Highlights
Fat embolism is defined as the mechanical obstruction of blood vessels by circulating fat particles[1,2]
We evaluated the area occupied by fat emboli in lung sections treated for the different techniques using light microscopy (Olympus BX51)
The three techniques kept the tissue morphology tissue components were more recognized at lower magnifications in the OsO4 technique, as they stained in different colors, being the chromic acid, the technique showing the least differentiation (Fig. 1)
Summary
Fat embolism is defined as the mechanical obstruction of blood vessels by circulating fat particles[1,2]. Among the various techniques used for lipid demonstration in frozen sections of fresh or formalin-fixed tissues, the solvent dyes Sudan III and IV8,9 were the first to be used (e.g.10–12). In paraffin-embedded tissues, osmium tetroxide (OsO4) has been for decades the technique of choice for histological demonstration of fat embolism due to its high quality[20,21,22,23,24]. Tracy & Walia (2002) have described www.nature.com/scientificreports another post-fixation technique that uses chromic acid to fix lipids by transforming fat emboli in organometallic complexes insoluble in organic solvents and stainable in paraffin sections[4]. Some advantages of chromic acid when compared with OsO4 may include its lower price, higher capacity of tissue penetration, and its lower degree in toxicity in some GHS hazard statements. The histologic detection of lung fat emboli has been used for decades in forensic practice to demonstrate antemortem violence, as cardiac function is needed, even for a short time before death, to allow the circulation of fat emboli to the lungs[10,31,32,33]
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