The Development of the Human Hyoid-Larynx Complex Revisited

Objectives/Hypothesis: The hyoid-larynx complex is highly prone to anatomical variation. The etiology of anatomical variants such as Eagle's syndrome and the aberrant hyoid apparatus can be explained from embryonic development. Modern textbooks state that the hyoid bone body develops from the second and third pharyngeal arch cartilages, and that thyroid cartilage derives from the fourth and sixth arch cartilages. This description, however, is incompatible with various anatomical variants, and it is unclear whether it was based on observations in human embryos or on comparative embryology. Study Design: 14 human embryos from the Carnegie collection between Carnegie stage 17 and 23 (42-60 days) were selected based on their histological quality. Methods: Histological sections of the selected embryos were examined. Three-dimensional models were prepared in an interactive format. These anatomical models provide crucial spatial information and facilitate interpretation. Results: We observed a less-complicated development of the hyoid-larynx complex than is currently described in textbooks. The body of the hyoid bone originates from a single growth center, without overt contributions from second and third pharyngeal arch cartilages. The fourth and sixth arch cartilages were not detected in human embryos; the thyroid and cricoid cartilages develop as mesenchymal condensations in the neck region. Conclusions: Despite new research techniques, theories about hyoid-larynx complex development from the beginning of the 20th century have not been refuted properly and can still be found in modern literature. Based on observations in human embryos, we propose a new and relatively simple description of the development of the hyoid-larynx complex to facilitate better understanding of the etiology of anatomical variants.