Genia,

I have experienced this problem several times at several different hospitals.  I don't feel like we've ever come up with an answer, but several explanations that have been given to me are: 1)  water trapped between the section and the slide - when the slide is put onto the hot plate, it cooks the tissue in that area  2) water contamination in the xylene - when the sections hit the hot paraffin, the areas with water are cooked.

I can't explain why it only happens on certain types of tissue.  In fact, it may be happening on other types of tissue as well.  When our pathologists looked more closely at the bigger stuff, they also noticed these pale areas.  Good luck and let us know if you find the cause.

Laurie Colbert