Detection of Muscle Fiber Orientation During Human Tongue Development: Analysis Using Diffusion Tensor Imaging

Area of Science:

• Developmental Biology
• Neuroscience
• Anatomy

Background:

• Tongue muscles, intrinsic and extrinsic, are crucial for complex movements.
• Previous gross and histological studies had limitations in distinguishing these muscles and their developmental timelines.
• Accurate differentiation timelines are essential for understanding congenital tongue abnormalities.

Purpose of the Study:

• To analyze embryonic tongue muscle fiber orientation using diffusion tensor imaging (DTI).
• To establish differentiation timelines for intrinsic and extrinsic tongue muscles.
• To evaluate the capabilities and limitations of DTI in embryonic muscle development studies.

Main Methods:

• Utilized diffusion tensor imaging (DTI) and 7-Tesla magnetic resonance imaging (MRI) on 29 human embryonic and fetal specimens.
• Employed fiber tractography to track muscle fiber orientation and fractional anisotropy values.
• Correlated DTI findings with serial histological sections for validation.

Main Results:

• Tongue muscles began differentiating into myotubules around Carnegie stage (CS) 19, with many identifiable by CS23.
• Intrinsic and extrinsic muscles showed similar differentiation timelines, starting at CS19.
• DTI allowed for clear distinction between most extrinsic and intrinsic muscles based on fractional anisotropy and fiber orientation, though precise quantification was limited.
• Histology confirmed specific muscle identification (vertical, transverse, hyoglossus, genioglossus) at CS19.

Conclusions:

• Intrinsic and extrinsic tongue muscles differentiate concurrently during early embryonic development (CS19).
• Diffusion tensor imaging (DTI) is a valuable tool for assessing embryonic tongue muscle development, capable of detecting immature muscle tissues.
• DTI has limitations in precise quantification but offers insights into muscle differentiation and orientation, with potential applications in other developing tissues.