Topical Aluminum Chloride and Monsel's Solution Block Toluidine Blue Staining in Mohs Frozen Sections: Mechanism and Solution.

BACKGROUND: A 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 surgeon's accurate reading. The authors hypothesize that topical hemostatic agents, aluminum chloride, and Monsel's solution are the causative factors.

OBJECTIVE: To 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 METHODS: Leftover Mohs frozen sections and specimens were treated with aluminum chloride or Monsel's solution and processed with routine Mohs histology.

RESULTS: Nonstaining artifact is reproduced in aluminum chloride or Monsel's 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.

CONCLUSION: By 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.