[Histonet] artifact quiz ANSWER

[Marshall Terry Dr, Consultant Histopathologist]

Everyone has sent an answer to my email address rather than through histonet it seems (as was suggested by Herb at the website), so others will not know what has been suggested..
Residual water, paraffin and air bubbles seem to be the favoured suggestions.

However the answer is bleaching by light, as I accidentally left my microscope on overnight with this area underneath. It was perfectly stained (by that I mean normal for here:-)) the day prior.

The real clue, as alluded to by several was the perfect circle plus the fact that the H had survived to some extent, the E going walkabout, and therefore anything suggesting a barrier to staining is ruled out.

Highly commended is:

Could it be that someone had left the section
on a fluorescence microscope with epi-illumination
from a high power objective, causing photobleaching
of the eosin in a circle that is visible at lower
power? This commonly happens if you spend too long
looking at one particular area by fluorescence
microscopy. I suppose it could happen with
ordinary illumination, given enough time.

          John Kiernan

And, almost there was:

Looks like an air bubble was trapped under the tissue and it popped 
sometime during the staining process. It reminds me also of an area on a 
fluorescent labelled section that has been quenched, but of course this 
is not fluorescence.

Kathleen Spencer, HT ASCP

Also almost there, except that the answer is the exact opposite, as it is light bleaching rather than light staining: 

If it is a complete circle of light staining (cannot tell from your 
picture) it is lack of deparaffinization.

Ada T. Feldman, MS, HT/HTL(ASCP)

BTW, have left microscope on before, but never seen this effect.
Hope you all enjoyed.

Dr Terry L Marshall, B.A.(Law), M.B.,Ch.B.,F.R.C.Path
 Consultant Pathologist
 Rotherham General Hospital
 South Yorkshire
 England
        terry.marshall <@t> rothgen.nhs.uk