Redefining the Fate of the Six Auricular Hillocks: A New Model of Auricular Development

BACKGROUND: The developmental fate of the 6 auricular hillocks has remained controversial, particularly regarding the origins of the tragus and helical crus. Based on clues from their congenital anomalies, we reinterpreted hillock fate and proposed a new model of auricular development. METHODS: Forty-seven serial auricular images from Streeter's Carnegie Collection were analyzed. Ten representative images with distinct hillock boundaries were selected. The 6 hillocks were serially traced to determine their migration, transformation, and definitive derivatives. RESULTS: H1 gives rise to the inner tragus and inferior one-third of the outer tragus; H2 to the helical crus and superior two-thirds of the outer tragus; H3 to the anterior helix; H4 to the superior helix and superior crus of the antihelix; H5 to the posterior helix and antihelix, including its inferior crus; and H6 to the antitragus and earlobe. The tragus thus derives from both H1 and H2, whereas the helical crus derives exclusively from H2. An anterior extension from the base of the H6 conchal bulge joins the H6 lateral bulge, indicating that the earlobe is derived entirely from H6. The superior crus develops from the H4 conchal bulge during the early fetal stage in close association with superior helix development. These findings were integrated into a new model of auricular development. CONCLUSIONS: This study redefines the fate of the 6 auricular hillocks and provides an embryologic basis for understanding congenital auricular anomalies and their reconstruction.