Morphological Analysis and Ontogenesis of the Cheek SMAS

Objectives: The aim of this study was the morphological analysis of the adult cheek SMAS in comparison with the fetal anlage.
Methods: Cheek tissue blocks over the parotidean and praeparotidean region were collected post mortem from five (three male and two female) formalin fixed donor bodies. Serial histological sections were cut, stained in Azan and Haematoxylin and Eosin and digitised. Histological embryological facial serial sections of the University Witten/Herdecke of two fetuses at 12 and 15 weeks of development have been compared to adult specimens. Regional differences were histological analysed. Digitalisation and three dimensional reconstruction of the adult SMAS structures was performed using AutoCAD.
Results: Adult cheek SMAS showed regional morphological differences between the prae- and the parotidean region. The praeparotidean SMAS (type I¹) architecture consisted vertical into the dermis aligned fibrous septa. The fibrous septa of the parotidean region (type I²) were aligned parallel to the skin level having short transverse communicating cords. Isolated muscle cells were into the fibrous septa. The three dimensional reconstruction revealed a fibrous network of communicating spaces bolstered with fatty tissue. Fetal SMAS was a plane muscle anlage crossing the cheek beginning retroauricular and inserting into the perioral muscles. The primordial SMAS conflated with the platysma muscle in the cheek region. There were no morphological similarities between the adult and the fetal SMAS.
Conclusions: Adult SMAS derives from a muscle anlage degeneration, which explains the isolated muscle cells in the fibrous septa. The alignment of the parotidean fibrous septa parallel to the skin level reflect the close relationship between the mimic muscles and the SMAS. Regional SMAS architectural differences need to be considered in the daily practice.