Question

Intraoperatively which stain is used to view following lesion:

• A. AgNo3
• B. Toluidine Blue
• C. Congo red
• D. Methylene blue

Hint:

Think of the metachromatic vital dye that dysplastic oral mucosa retains during surgery.

Answer 1

The Correct Option is B

Step 1: Identify the lesion. The clinical photograph shows a suspicious red/erythematous and ulcerated mucosal lesion of the oral cavity, the kind of premalignant/malignant area (e.g. erythroplakia, leukoplakia with dysplasia, or early oral squamous cell carcinoma) for which the surgeon needs to delineate the true margins during surgery.

Step 2: Recall the role of vital staining. A vital (in-vivo) stain selectively highlights dysplastic or malignant mucosa so the operating surgeon can map abnormal tissue and guide where to take the biopsy or set the resection margin intraoperatively.

Step 3: Choose the correct dye. Toluidine blue is the classic vital stain used intraorally. It is a metachromatic, acidophilic dye that binds DNA/RNA; dysplastic and malignant cells have increased nuclear material and wider intercellular canals, so they retain the dye and stain a deep royal blue, whereas normal mucosa washes clean. This makes it ideal for identifying and viewing the lesion intraoperatively. Hence option B is correct.

Step 4: Exclude the distractors.
- AgNO3 (silver nitrate): a chemical cautery/escharotic agent used to control bleeding and burn off granulation tissue, not a vital stain for mapping oral malignancy.
- Congo red: stains amyloid (apple-green birefringence under polarised light) on histology slides; it is not an intraoral vital stain.
- Methylene blue: used for sentinel-node mapping and to stain Barrett oesophagus on chromoendoscopy, but the standard answer for viewing an oral premalignant/malignant lesion is toluidine blue.

Final answer: B. Toluidine Blue.