Ice crystal distortion of formalin-fixed tissues following freezing.

The inability of slowly frozen formalin-fixed tissues to reimbibe water normally on thawing accounts for the persistence of extracellular ice crystal spaces in such tissues and renders them useless for diagnostic microscopic examination. This phenomenon may be encountered by the surgical pathologist when tissues obtained for diagnosis are placed in formalin for fixation and the inadvertently frozen. The same type of ice crystal distortion was produced when formalin-fixed tissues were slowly frozen under laboratory conditions. The freezing artifact was not produced when formalin-fixed tissues were frozen in non-formalin-containing aqueous media.