Structure not visible on indirect laryngoscopy
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structure not visible on indirect laryngoscopy ENT exam anterior commissure subglottis
Here is a complete answer based on ENT textbooks and authoritative sources:
Structure NOT Visible on Indirect Laryngoscopy
The Classic Exam Answer: Anterior Commissure
The anterior commissure is the structure classically cited as not visible (or poorly visible) on indirect laryngoscopy (mirror laryngoscopy). This is because:
- The laryngeal mirror reflects the larynx from a posterior angle, and the anterior commissure - where both vocal cords meet anteriorly - is hidden behind the base of the tongue and the curve of the epiglottis.
- A large tongue base or inability to relax prevents the mirror from angling far enough forward to visualize it.
- As noted by Ento Key's indirect laryngoscopy resource: "The anterior commissure is an area that is often difficult to see, especially if the patient has a large tongue base."
Additional Structures with Limited/No Visibility
| Structure | Reason not visible |
|---|---|
| Anterior commissure | Hidden behind tongue base / epiglottic overhang; mirror angle cannot reach anteriorly |
| Subglottis | Below the plane of the vocal cords; mirror view is angled from above |
| Ventricles | Hidden under the overhanging false (vestibular) cords |
| Pyriform fossae (partially) | Lateral recesses; limited mirror angle |
The Merck Manual also notes: "Mirror laryngoscopy only provides a limited view of the subglottic larynx and proximal trachea."
What IS Visible on Indirect Laryngoscopy
For contrast, structures routinely seen include:
- Base of tongue
- Valleculae
- Epiglottis
- Aryepiglottic folds
- Arytenoid cartilages
- False (vestibular) vocal cords
- True vocal cords (movement assessed by asking patient to say "eee")
- Piriform sinuses
Clinical Significance
The anterior commissure's poor visibility on indirect laryngoscopy is clinically important because early glottic cancers at the anterior commissure can be missed. This is why direct laryngoscopy (microlaryngoscopy under GA) or flexible fiberoptic laryngoscopy is required for complete evaluation - especially when an anterior commissure lesion is suspected.
Summary for exams: The single best answer is the anterior commissure - it is the structure most commonly cited as not visible on indirect (mirror) laryngoscopy due to the angle limitations of the laryngeal mirror.
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