MLT GlobeHistopathology: Special stains
53 Histopathology MCQs on Special stains with answers and explanations.
Neutral lipids are to be demonstrated with Oil Red O. How should the tissue be sectioned?
Alcohols and clearing agents in paraffin and celloidin processing dissolve lipids, so frozen sections are used.
Verhoeff–Van Gieson staining of an arterial wall is requested. Which component is Verhoeff's iron hematoxylin intended to show black?
Verhoeff's method stains elastic fibres black; the Van Gieson counterstain colours collagen red and muscle yellow. It is used to assess elastic laminae in vessels.
The main aim of histochemistry is to:
Histochemistry uses chemical reactions to show where substances such as glycogen, iron, enzymes or lipids occur in tissue while preserving morphology.
Neutral fat in a frozen section is best demonstrated with:
Oil red O is a lysochrome that dissolves in lipid, staining it red. Trichrome shows connective tissue, PAS carbohydrates and Perls' ferric iron.
Which stain at pH 2.5 is used to show acid mucins blue?
Alcian blue binds carboxylated and sulfated mucins. Oil red O shows fat and von Kossa shows calcium deposits.
Reticulin fibres (type III collagen) in liver or bone marrow are demonstrated by:
Reticulin fibres are argyrophilic and appear black with silver methods. Masson–Fontana is for melanin and Ziehl–Neelsen for acid-fast bacilli.
A lung section from a city dweller shows black particles in macrophages. Which pigment is exogenous (from outside the body)?
Inhaled carbon is an exogenous pigment. Hemosiderin, bilirubin and melanin are endogenous pigments produced in the body.
A yellow-brown granular pigment accumulating with age in heart and liver cells, known as 'wear and tear' pigment, is:
Lipofuscin is an insoluble residue of lipid peroxidation in lysosomes. Hemosiderin is iron-positive with Perls'; melanin is bleached by oxidizers.
Which of the following is NOT a lipid?
Proteoglycans are protein cores with glycosaminoglycan chains, found in cartilage and ground substance. Lecithin and phosphatidylethanolamine are phospholipids; cerebrosides are glycolipids.
To distinguish collagen, muscle and fibrin in one section, a laboratory uses:
Trichrome methods use two or more acid dyes of different molecular size to colour collagen, muscle and fibrin differently.
Which statement about the periodic acid–Schiff (PAS) reaction is INCORRECT?
PAS positivity is magenta. Periodic acid oxidizes glycols to aldehydes, which react with Schiff's reagent; it is often paired with Alcian blue to separate acid and neutral mucins.
Which reagent would extract lipids from a tissue section?
Organic solvents such as acetone, alcohol, chloroform and xylene dissolve lipids. Calcium formalin is used to preserve lipids, especially phospholipids.
In the Ziehl–Neelsen stain, acid alcohol serves as the:
Acid-fast bacilli retain carbol fuchsin after acid alcohol, while other material is decolorized and counterstained blue. In the Gram stain, acetone or alcohol is the decolorizer.
A silver impregnation of a lymph node shows a fine black branching network supporting the lymphocytes. This supporting network is composed of:
Reticular (type III collagen) fibres form the argyrophilic stroma of lymph nodes, spleen, liver and marrow. Elastic fibres are demonstrated with orcein or Verhoeff, not silver.
A single slide must show acid mucins and neutral mucins in different colours. Which combined method is used?
In Alcian blue–PAS, acid mucins stain blue, neutral mucins magenta, and mixtures purple. Sudan black is for lipids and Best carmine for glycogen.
In a Fite-stained skin biopsy from a leprosy patient, positive bacilli appear:
Fite (a modified acid-fast method with oil protection) stains M. leprae red with carbol fuchsin, against a blue counterstain.
Which acid-fast method is the most sensitive for screening smears for mycobacteria?
Fluorochrome staining is read at low magnification, so more fields are scanned, making it more sensitive than carbol fuchsin methods such as Ziehl–Neelsen or Kinyoun.
Argentaffin cells, such as enterochromaffin cells, are named for their ability to reduce which metal salt without an external reducer?
Argentaffin granules reduce ammoniacal silver directly to black metallic silver. Argyrophil cells need an added reducing agent.
Which natural dye is used to demonstrate elastic fibres?
Orcein (Taenzer–Unna) stains elastic fibres brown. Sudan dyes are for lipids.
Perls' reagent, freshly mixed potassium ferrocyanide and hydrochloric acid, gives a positive blue reaction with:
Acid releases ferric iron from haemosiderin, which reacts with ferrocyanide to form Prussian blue.