The Vermilion Canal: A Longitudinal Potential Space Beneath the Vermilion Margin Explaining One Point, Linear Filler...

Clinicians frequently observe that filler deposited at the vermilion border can "track" for a long distance along the lip margin from a single entry point, producing a continuous, sharply defined border line. This behavior suggests an anatomic conduit at the mucocutaneous junction.

To identify a reproducible longitudinal structure beneath the vermilion margin (the "vermilion canal") and to characterize the pattern of one-point, linear tracer spread along the vermilion border in the upper and lower lips.

Ten adult cadavers underwent dyed gel-filler tracer injection using 1 puncture site per lip (upper and lower). After injection, the lips were examined for macroscopic tracer distribution. Layered dissections and targeted cross-sections were performed to localize the tracer plane and define anatomic boundaries relative to the vermilion margin and orbicularis oris.

In 9 of 10 cadavers (90%), tracer propagated as a continuous longitudinal column immediately deep to the vermilion border with limited dispersion into the central lip. Dissection demonstrated a canal-like potential space aligned with the vermilion border, constrained by connective-tissue septa and closely related to the superficial orbicularis oris. The configuration was present in both upper and lower lips in positive specimens. One cadaver showed an indistinct plane with irregular spread.

A consistent longitudinal potential space beneath the vermilion margin can facilitate long-segment, linear filler distribution after single-entry injection. The "vermilion canal" concept offers a simple anatomic explanation for border tracking and may support a streamlined, plane-specific approach for creating a crisp vermilion border line while maintaining vigilance for vascular variability.