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Transient connection or origin of the inferior pharyngeal constrictor during fetal development: A study using human
Shogo Hayashi1, Hidetomo Hirouchi2, Gen Murakami3
1Department of Anatomy, School of Medicine, International University of Health and Welfare, Narita, Chiba, Japan.
Insights
Transient aberrant connections of the inferior pharyngeal constrictor (IPC) muscle to adjacent muscles were observed in fetal development. These connections appear to resolve, leading to typical adult anatomy.
Area of Science:
- Embryology
- Anatomy
- Developmental Biology
Background:
- The inferior pharyngeal constrictor (IPC) muscle is a key component of the pharyngeal wall.
- Understanding the developmental origins and variations of the IPC is crucial for anatomical accuracy.
Purpose of the Study:
- To investigate aberrant muscular connections during the prenatal development of the inferior pharyngeal constrictor (IPC).
- To analyze the transient origins of the IPC and their potential resolution into adult morphology.
Main Methods:
- Examination of serial sagittal sections from 37 human embryos and fetuses (6-15 weeks gestation, 15-115mm crown rump length).
- Detailed observation and documentation of muscular origins and connections of the IPC.
Main Results:
- Aberrant connections of the IPC to sternothyroideus, thyrohyoideus, and cricothyroideus muscles were identified in a significant proportion of specimens.
- These aberrant origins were often transient, appearing to resolve as fetal development progressed.
- A digastric muscle-like appearance was noted in some specimens due to tendinous bands connecting the IPC to the cricothyroideus muscle.
Conclusions:
- Aberrant origins of the IPC are likely transient developmental variations, possibly due to growth discrepancies between cartilage and muscles.
- These variations typically resolve, leading to the standard adult IPC morphology by the mid-to-late prenatal period.
- The findings suggest significant plasticity and growth rate variations in laryngeal structures during development.
Abstract:
The inferior pharyngeal constrictor (IPC) originates from the thyroid and cricoid cartilages and inserts to the pharyngeal raphe. In serial sagittal sections of 37 embryos and fetuses at 6-15 weeks (crown rump length 15-115mm), we found (1) the IPC connecting to the sternothyroideus and thyrohyoideus muscles (16 fetuses at 6-11 weeks) or (2) the cricothyroideus muscle (6 fetuses at 12-15 weeks) in addition to the usual cricoid origin. These aberrant connections were most likely to be transient origins of the IPC not from a hard tissue but nearby striated muscles. In four of the latter six specimens, a tendinous band from the IPC inferior end connected to the cricothyroideus muscle to provide a digastric muscle-like appearance. These aberrant connections with nearby muscles seemed to become separated by a growing protrusion of the thyroid cartilage. Therefore, these aberrant origins were, even if developed, most likely to be "corrected" to the adult morphology during midterm or late prenatal period. The aberrant or transient origin of the IPC seemed to result from a discrepancy in growth of the cartilage and muscles. Such a discrepancy in growth seems to resemble the IPC wrapping around the superior cornu of thyroid cartilage. In addition, a final or adult-like morphology was found in two of the present 37 fetal specimens. It seemed to suggest a significant redundancy in growth rate of the laryngeal structures.
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