MRI Analysis Of Palate Fusion In Human Fetal Specimens

Objectives: For almost 50 years, human soft palate formation was believed to occur primarily by the mechanism of merging. We recently reported novel histological evidence in human specimens in the late embryonic-early fetal period that show the alternative mechanism of fusion occurs in the soft palate similar to the hard palate. The aim of this follow-up study is to sample older specimens between 64-84 days post-conception to determine the maximum age where remnants of the medial edge seam can be seen in the hard and soft palate using MRI.
Methods: Seven whole human heads aged 64-84 days post-conception underwent MRI scanning (Human ethics protocol H08-02576). Contrast was improved using 3 mM Gadolinium. Slice thickness was 53-75µm resulting in 1-1.5 hours of scan time per specimen. Scans were imported to the 3D-Slicer program v. 4.4 (NIH), structures of interest were traced in sequential slices and 3D volume renderings of the structures were created.
Results: We confirm the presence of a seam extending throughout the hard palates in 64-84 day specimens. The most posterior part of the soft palate in the 64-day specimen had a seam similar to our histological analysis. Our data supports our preliminary histological study that the soft palate follows a developmentally more rapid fusion compared to the hard palate and that the hard palate retains midline epithelial remnants until at least 84 days gestation.
Conclusions: This study extends our analysis of human soft palate development through the early fetal period. Resolution and contrast of the MRI scans is sufficient to detect thin epithelial layers and can be used to document palate fusion in intact specimens; However, MRI is not sufficiently detailed to accurately trace individual muscles or nerves.