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Pathology · single question

A mucocele on the lower lip appears bluish. What is the MOST accepted explanation for this color?

  1. Melanin deposition in the basal cell layer
  2. The overlying tissue and pooled mucin scatter light so that only the blue wavelengths are reflected back
  3. Extravasated red blood cells in the connective tissue
  4. Vascular congestion within the lesion
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Correct answer: B. The overlying tissue and pooled mucin scatter light so that only the blue wavelengths are reflected back

  • A. Melanin produces brown-to-black pigmentation, and a deep melanin deposit appears blue-grey but does not fluctuate or rupture.
  • B. CORRECT. The bluish translucency of a mucocele is an OPTICAL effect (the Tyndall effect). The pool of mucin sits beneath a thin, intact layer of tissue; longer wavelengths (red) are absorbed by the deeper tissue while the shorter blue wavelengths are scattered back to the observer. The same physics explains why superficial veins look blue and why a blue nevus appears blue.
  • C. Extravasated red cells produce ecchymosis, which changes color over days as hemoglobin degrades.
  • D. Vascular congestion produces a red-purple, blanchable lesion (a hemangioma or varix), not the translucent blue of a mucin pool.

Note: ⚠️ FLAG FOR THE GROUP: this file keys this question two different ways (item 22 = mucoid content/optical; item 122 = vascularity). Neville and standard oral pathology texts attribute the blue color to the Tyndall optical effect of the mucin pool. Go with the optical explanation.

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