Histomorphological analysis of the superficial musculoaponeurotic system in Macaca mulatta species.

INTRODUCTION: The superficial musculoaponeurotic system (SMAS) is a well described facial functional unit in humans. SMAS connects mimic musculature to the skin having many implication in facial mimic expression. One of the various morphological and physiological analogies in human and Macaca mulatta species is the facial mimic. The present study analyzed Macaca mulatta species SMAS morphology and its facial topographical differences and compared this with human SMAS tissue morphology. MATERIAL AND METHODS: Macaca mulatta full-graft tissue blocks of skin, subcutaneous tissue and mimic muscles from five topographical different facial regions (Regio Temporalis, Regio Buccalis, Regio Infraorbitalis, Regio Angulus Oris and Regio Mandibularis) were collected postmortem from eight individuals (n = 8) at the German Primate Center, Leibniz Institute for Primate Research in Göttingen (DPZ) and studied histologically. Haematoxylin-eosin and azan stained histological serial sections of full-graft tissue blocks were analyzed and SMAS topographical differences evaluated. RESULTS: SMAS typical tissue morphology was recognized in all Macaca mulatta histological serial sections (n = 780). Regio Infraorbitalis Macaca mulatta SMAS (MmSMAS) morphology was similar to human infraorbital SMAS morphology (type I SMAS). Suborbicularis oculi fat pad was recognized in Macaca mulatta samples. Human type I similar SMAS morphology was demonstrated over Macaca mulatta Regio Temporalis and Regio Buccalis. Regio Angulus Oris and the cranial area of the Regio Mandibularis presented human type II similar SMAS morphology. Type IV MmSMAS was closely related to the parotid gland tissue presence. The cervical area of the Regio Mandibularis presented human type V similar SMAS morphology. CONCLUSIONS: SMAS is a complex fibro-musculo-adipose tissue network and probably an important pivot in Macaca mulatta facial system supporting mimic expression. This study provided insights into MmSMAS typology and similarity with human SMAS tissue morphology.