Topical Aluminum Chloride and Monselʼs Solution Block Toluidine Blue Staining in Mohs Frozen Sections: Mechanism and Solution

BACKGROUNDA diminished-staining artifact is observed in some Mohs frozen sections that are stained in toluidine blue (T-blue). Such an artifact, not yet described in the literature, may interfere with a Mohs surgeonʼs accurate reading. The authors hypothesize that topical hemostatic agents, aluminum chloride, and Monselʼs solution are the causative factors. OBJECTIVETo evaluate the aforementioned topical hemostatic agents as a potential cause of the nonstaining artifact, to propose the mechanism associated with this phenomenon, and to develop a method to prevent or rectify the problem. MATERIALS AND METHODSLeftover Mohs frozen sections and specimens were treated with aluminum chloride or Monselʼs solution and processed with routine Mohs histology. RESULTSNonstaining artifact is reproduced in aluminum chloride or Monselʼs solution–treated ex vivo skin specimens. The authors found that ethylenediaminetetraacetic acid (EDTA), a chelating agent, can reverse the staining blockage. Such a finding suggests that aluminum or ferric cations bind to tissue and subsequently inhibit T-blue from interacting with the tissue. Direct binding of ferric cations to the tissue section is demonstrated with Prussian blue iron staining. CONCLUSIONBy rinsing Mohs frozen sections in an EDTA solution before T-blue staining, the authors could prevent hemostatic agent–induced nonstaining. Applying an EDTA wash and restaining the slides can correct the same artifact.