Masson Fontana

Classification: pigment stain

Mechanism of staining: histochemical

Purpose: stain hemosiderin

Control tissue: spleen, bone marrow


Melanin: black or brown 

Nuclei: red

Cytoplasm: light red



Special Considerations:

Argentaffin reactions, unlike argyrophil reactions, require no extraneous reducer.

Rinse glassware before use with distilled water avoid contamination with free metal ions. Also use plastic forceps or wax coated forceps to handle slides.

                                                      


REAGENT

PURPOSE

MECHANISM OF STAINING

SOURCE OF ERROR

Gram’s Iodine

Oxidation

Suppresses sulphydryl and tryrosine groups and exposes phenol groups.

Omitted: Melanin will not be demonstrated.

Too short: Trace amounts of melanin may not be demonstrated.

Too long: Will not affect staining.

5% Sodium thiosulphate

Bleaching

Removes brown discoloration

Omitted: Discoloration in counterstain. Tissue sections will be discoloured.

Too short: Sections may be slightly discoloured.

Too long: Will not affect staining.

Methenamine silver (hexamine silver)

Impregnation

 

o      Silver nitrate

o      Hexamine

o      Borax

Forms complexes at the phenol groups

Omitted: Melanin will not be demonstrated.

Too short: Trace amounts of melanin will not be detected.

Too long: Non-specific staining may occur.

Gold chloride

Tones collagen

 

Lays down gold in place of silver to remove any brown colour in other tissue components.

 

Ion exchange

Omitted: Collagen will remain golden- brown. Toning is optional.

Too short: Will not affect staining.

Too long: Trace amounts of fungus may not be detected because gold chloride will start to remove silver staining.

Sodium thiosulphate (hypo)

Fixation

Ion exchange of silver with gold.

Omitted: Non-specific blackening of slide over time due to remaining unreduced silver.

Too short: Some non-specific blackening of slide over time.

Too long: Will not affect staining.

Nuetral red or Light green

Counterstain

Ionic bonding

Omitted: Background will not be demonstrated.

Too short: Background will be difficult to see.

Too long: May obscure melanin staining.

 

 

Unbleached Control


To confirm the presence of melanin, bleaching is performed on a control slide, using a strong oxidizing agent such as potassium permanganate or hydrogen peroxide. This procedure is performed as follows:

·         Two consecutive sections are cut

·         Bleaching of melanin is done on one slide only

·         Perform Masson Fontana technique as per usual on both slides


Bleached Control

·        If the bleached slide is MF negative, and the unbleached slide is MF positive, the tissue likely contains melanin. 


References

Officer B. HIML251 Lecture notes: Silver Stains: Grocott’s Methenamine Silver, Jone’s Methenamine Silver, and Masson Fontana, March 18, 2009

University of Vermont Pathology. Masson Fontana Stain for Melanin. 2008. [cited 2009 April 6]. Available from http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab2/Examples/exfontana.htm

Yawney, L. HIML 251 Theory Notes: Masson Fontana. The Michener Institute for Applied Health Sciences, 1989.