Embryology of Laryngeal Cartilages
The laryngeal cartilages develop as mesenchymal condensations in the neck region during weeks 4-8 of embryonic development, with the thyroid and cricoid cartilages arising directly from mesenchyme rather than from pharyngeal arch cartilages as traditionally taught. 1
Developmental Timeline and Origin
Early Formation (Weeks 4-6)
- The respiratory primordium buds off from the primitive foregut and grows caudally on a lengthening stalk during Carnegie stages 16-17 2
- The cephalic end of this stalk develops into the glottis and infraglottis, while the remainder becomes the trachea 2
- Pharyngeal mesoderm compression creates an epithelial lamina with a pharyngoglottic duct along its dorsal border 2
Cartilage Development (Weeks 6-8)
The thyroid and cricoid cartilages develop as mesenchymal condensations without direct contributions from the fourth and sixth pharyngeal arch cartilages, contrary to traditional textbook descriptions. 1 This represents a critical revision of embryological understanding based on direct observation of human embryos.
- Cricoid cartilage: Chondrifies bilaterally from a single center in the ventral arch of a precartilaginous template that encircles the infraglottic cavity; the two sides meet to form the dorsal lamina 2
- Thyroid cartilage: Each half chondrifies from two separate centers 2
- Arytenoid cartilages: Each arytenoid chondrifies from a single center 2
Laryngeal Cavity Formation (Week 8, Stage 23)
At approximately 8 postovulatory weeks (Carnegie stage 23), the laryngeal cavity comprises three distinct regions 3:
- The coronal and parts of the sagittal clefts of the vestibule (which later unite at the laryngeal inlet)
- The ventricles, which are not yet completely formed at this stage
- The subglottic cavity, which appeared in earlier stages
The dissolution of the epithelial lamina and development of the ventricles are the characteristic events of stage 23. 3 This disruption is an active process involving cellular rearrangement and growth, not cell loss.
Important Developmental Details
Ventricle Formation
- Ventricles begin as solid outgrowths in stage 20 3
- They do not represent fifth pharyngeal pouches, as sometimes incorrectly stated 3
- Bilateral pouches arising from the caudal end of the cecum form the ventricles, with their lower lips becoming the vocal folds 2
Muscle Development
- Anlagen for intrinsic laryngeal muscles appear during stage 17 2
- Individual muscle sites are recognizable by stage 23 2
- Myofibrils are present by the 12th week 2
Clinical Implications
Understanding the true embryological origin of laryngeal cartilages is essential for explaining anatomical variants and congenital anomalies. 1 The simplified developmental model—where cartilages arise from mesenchymal condensations rather than pharyngeal arch derivatives—better explains the etiology of anatomical variants encountered in clinical practice.
The pharyngeal mesoderm surrounding the laryngeal cavity gives rise to both the laryngeal cartilages and intrinsic musculature 2, establishing the integrated structural-functional unit of the larynx.