urgical and minimally invasive lipenhancement procedures are frequently performed to increase volume or to enhance the contour of the upper and lower lips. [1][2][3] Hyaluronic acid (HA)-based soft-tissue fillers are the treatment of choice for aesthetic improvement of the lips, as they offer immediate effects with minimal recovery time, have low risk of scarring or permanent tissue damage, and are highly accessible and affordable. Lip filler injection techniques include using sharp-tipped needles or blunt-tipped cannulas in vertical or horizontal injection directions, by introducing small boluses or with linear threading. [4][5][6][7] Results of HA lip injections are highly variable and depend on the patient's aesthetic desires, ethnic background, age, panfacial treatment plan, budgetary considerations, and the skill of the injector.In 2009, Rohrich and Pessa 8 described a layer of fatty tissue deep to the orbicularis oris muscle (OOM) that was predominantly identified within the cutaneous portion of both the upper and Background: Aesthetic soft-tissue filler injections for lip enhancement are popular and performed throughout the world. When injecting lips with a cannula, as the cannula is advanced, resistance is perceived in consistent locations, potentially indicating boundaries between intralabial compartments. Objective: We aimed to investigate whether intralabial compartments exist and, if so, to describe their volumes, location, boundaries, and dimensions. Methods: This cadaveric study investigated a total of 20 human body donors (13 male, seven female) with a mean (SD) age at death of 61.9 years (23.9) and body mass index of 24.3 kg/m 2 (3.7). The investigated cohort included 11 White donors, eight Asian donors, and one Black donor. Dye injections simulating minimally invasive lip treatments were conducted. Results: Independent of sex or race, six anterior and six posterior compartments in the upper and lower lip were identified, for a total of 24 lip compartments. Compartment boundaries were formed by vertically oriented septations that were found in consistent locations. The anterior compartments had volumes ranging from 0.30 to 0.39 cc; the posterior compartment volume ranged from 0.44 to 0.52 cc. The compartment volumes were larger centrally and decreased gradually toward the oral commissure.
Conclusions:The volume and size of each of 24 compartments contribute to the overall appearance and shape of the lips. To achieve a natural lip shape preserving aesthetic outcome it may be preferable to administer the volumizing product using a compartment-respecting injection approach.