Changes in Subplatysmal Anatomy with Aging: A Longitudinal Imaging Study

Goals/Purpose: The subplatysmal structures, such as the submandibular gland (SMG) and paired anterior digastric muscles (ADM), play an essential role in submandibular fullness with aging. Subsequently, this has resulted in various targeted procedures to enhance and rejuvenate the aging neck. However, the current understanding of the volumetric changes is limited, with findings isolated to individual structures. Therefore, this study aimed to expand the current knowledge of the age-associated changes to the SMG and ADM by comprehensively examining the changes in the surrounding anatomy while longitudinally incorporating patient-related factors to improve the aesthetic surgeon's understanding, foster shared decision-making and optimize outcomes.

Methods/Technique: This retrospective, longitudinal study utilized MRI segmentation (Vitrea) to calculate the SMG's total and inframandibular volume, along with the ADM and mandibular volume. Additionally, various morphological measurements were obtained and analyzed along with patient demographics to track their longitudinal effects on the SMG and ADM comprehensively. Subjects with at least two prior MRIs of the head and neck separated by a minimum of four years were used for analysis. Those with pathology or artifact compromising the anatomy of interest were excluded.

Results/Complications: The study included 75 subjects (Females n=41; Males n=34) with a mean age of 51.9 (range 7-81) and 59.3 (range 16-89) at time point one and two, respectively (mean difference 7.4; range 4-15). Mean total SMG and inframandibular SMG volume increased from 8.34 ml and 7.01 ml to 9.03 ml (p < 0.001) and 7.81 ml (p < 0.001), respectively. The inframandibular SMG volume had a mean rate of change of 0.12 ml/year, with the majority of growth occurring before 60 years. The total and inframandibular height of the gland increased from 33.93 mm and 26.21 mm to 34.82 mm and 27.91 mm (p < 0.0001). The mean ADM volume increased from 2.41 ml to 2.43 ml, while the length of the ADM (digastric fossa to hyoid bone) increased from 37.12 mm to 39.42 mm (p = 0.0072). The mean vertical distance between the inferior border of the mandible and the hyoid bone increased from 22.80 mm to 24.44 mm (p = 0.83). Male gender and overweight or obese BMI class were associated with significantly higher SMG and ADM volumes.

Conclusion: Our findings suggest that the SMG increases in volume, with most growth occurring before age 60 and greater than 70% of the gland below the mandible in subjects 50 years and older. Further, while the volume of the ADMs did not increase with age, the length of the ADM and the distance between the mandible and hyoid bone did, which may contribute to the perceived bulkiness of the muscle belly. Rejuvenating the aging neck has been and will continue to be a timeless pursuit sought out by many. As we deepen the current understanding of the age-related changes to the deep subplatysmal structures, the plastic surgeon may approach each patient with increased insight to develop a patient-centered operative plan, ideally targeting their less-than-ideal anatomy and optimizing outcomes following cervical rejuvenation.