Methods/Technique: Eleven fresh cadaver heads were obtained and the skin was removed. Each compartment of fat was weighed along with the submandibular gland, which was also measured and weighed. Fat in the superficial compartment was found between the skin and the platysma muscle. This was further sub-compartmentalized into suprahyoid and infrahyoid fat. The intermediate fat was found deep to the platysma and between the medial edges of the platysma in the midline. This fat was typically in an hour-glass shape and also fell into suprahyoid and infrahyoid compartments. The deep layer of fat in the neck was bordered superficially by the anterior belly of the digastric and the submandibular gland. Because of its adherence to deeper structures and small volume relative to the superficial and intermediate compartments, it was not removed or weighed.
Dye injection studies were performed in four specimens. Methylene blue was injected subcutaneously through a submental injection site, and the dye was allowed to diffuse through the tissue planes over 24 hours.
Results/Complications: Of the eleven specimens dissected, four were male and seven were female. All patients were elderly, with age range from 64-87 (mean, 73.0 years).
The superficial infrahyoid compartment contained 15% (±8.3%) of the total fat and glandular complement of the neck. The superficial suprahyoid compartment contained 29.7% (±11.2%) of the glandular and fat complement of the neck.
The intermediate compartment consisted of four sub-compartments, the infrahyoid central, the infrahyoid lateral, the suprahyoid central and the suprahyoid lateral. The infrahyoid central contained 6.0% (±4.2%) of the total subcutaneous soft tissue complement. The infrahyoid lateral subcompartment contained 7.6% (±1.4%) of the fat and glandular complement. The suprahyoid central contained 9.1% (±4.9)% of the total subcutaneous soft tissue complement, and the suprahyoid lateral contained 8.0% (±4.1%) of the total subcutaneous soft tissue complement.
The submandibular glands weighed an average of 9.4 g (±3.2 g), representing 24.5% (±14.4%) of the total subcutaneous soft tissue complement.
Gender differences were also investigated. In female cadavers, 51% of the fat and glandular content was found in the superficial compartment, while in males, only 35% of the fat was in the superficial compartment. Both genders demonstrated a similar amount of fat in the intermediate compartment, which was approximately 1/3 (males 33%, females 29%) of the fat/glandular content of the neck. In males, 32% of the fat/glandular content was occupied by the submandibular gland, while this amount was only 20% in females.
Cadavers were also analyzed by age group. In the superficial compartment, those with ages 60-69 (n=4) had 40% of their fat, those aged 70-79 (n=4) had 50% of fat in the superficial compartment and those aged 80-87 (n=3) had 44% of their fat in this compartment. In the intermediate compartment, those with ages 60-69 had 28% of their fat, those aged 70-79 had 35% of fat in the intermediate compartment and those aged 80-87 had 33% of their fat in this compartment.
Dye injection studies demonstrated several findings. First, the superficial and intermediate fat compartments were continuous in both the anterior/posterior and superficial to deep planes. Dye staining was present throughout the superficial fat, the platysma and the intermediate fat. In patients that had larger volumes of fat in the neck, fat in the deeper compartments was stained less densely. However, dye staining was not present in the deep fat compartment in any specimen, demonstrating that the intermediate and deep compartments are distinct from one another. Dye injections also demonstrated that within the intermediate compartment, the lateral infrahyoid fat did not stain, suggesting this fat pad may be in an anatomically distinct plane within the neck.
Conclusion: In conclusion, our study represents an attempt at further classifying the clinically relevant fat compartments that are routinely encountered during surgical rejuvenation of the neck. Building on the work done by previous investigators, this study contributes another anatomical perspective, the goal being that an improved understanding of the anatomy will necessarily lead to improved surgical technique, more aesthetic results, and better satisfied patients.