Carnoy’s solution is a caustic mixture of chemicals (by volume: 60 % ethanol, 30 % chloroform, 10 % concentrated acetic acid). It is named after J.P. Carnoy, a 19th century Belgian cytologist who developed the mixture as a fixative for tissue samples. In some preparations a small amount of ferric chloride, FeCl3, is added to the mixture. More recently an alternative formulation of Carnoy’s solution, omitting chloroform (by volume: 75 % ethanol, 25 % concentrated acetic acid) has been used in medical applications (see below). Chloroform is suspected to be a potentially carcinogenic substance for humans and, therefore is considered as problematic in applications on humans.
Tissue fixation in the histology / pathology laboratory for a fair range of tissue types and purposes remains the main application of Carnoy’s solution.
In addition, the chemical properties of Carnoy’s solution make it a chemical agent for cauterization (‘chemical curettage’) of living tissues. In this capacity Carnoy’s solution is used as an additional topical treatment after surgical enucleation of bone cysts, in particular in the treatment of keratocysts / keratocystic tumours of the jaws and some other benign tumours of the jaws (ameloblastoma). The epithelial lining of keratocysts is difficult to remove completely and recurrence is therefore a common problem. Treating the surgical bed after enucleation with Carnoy’s solution appears to decrease recurrence rates compared with enucleation alone.
Application of Carnoy’s solution is thought to eliminate any remaining epithelial lining of a cyst and/or local microcycsts; the solution causes superficial local necrosis. In this way, it appears that enucleation combined with chemical cauterization can achieve recurrence rates similar to those of more radical surgical resection, with reduced morbidity. It is currently unclear if the ‘modified’ version of Carnoy’s solution without chloroform is as effective as the original composition.