Mesencephalic flexure

The mesencephalic flexure, within the cranial region, should be apparent and surrounded by a region of facial mesenchyme (Fig. 13, area outlined in black). 

The facial region is morphologically assessed for developmental integrity of the nasal prominence, optic and otic placodes, as well as the relative spatial distance between the placodes as it pertains to the formation of the mesencephalic flexure (Fig. 13). 

Fig. 13. Facial morphology. Normal embryo with facial structures highlighted nasal prominence (np, oval circle), optic placode (op, arroWi and otic placode (otp, arroWi, and mesencephalic flexure light dotted ared). The mesencephalic flexure is surrounded by a central facial region filled with mesenchymal cell populations darkrectangle aredi.

Subtle changes that could be attributed to delayed development, such as poorly defined optic or otic placode borders (Fig. 14b, arrow) or mesencephalic flexure appearing less full in the area (Fig. 14b, circle), are assigned a score of 4. 

A score of 3 is assigned when the nasal prominence is small, or in cases when there are small or misshapen optic or otic placodes (Fig. 14c, arrows). A score of 3 is also assigned when the mesencephalic flexure is irregularly shaped or it is small/narrow. Frequently, facial hypoplasia (reduced expansion/distance between the optic and otic placodes) accompanies this finding as the flexure abnormalities can indicate alterations in craniofacial mesenchyme populations. 

Mesencephalic flexure—Misshapen Mesencephalic flexure—Not evident... 

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