Preauricular: The term itself is purely descriptive, meaning “in front of the auricle” (the visible external part of the ear).
Pit/Dimple: The visible opening is referred to as a pit or dimple.
Fistula/Sinus: The sinus or fistula refers to the entire tract, which can extend for several millimeters or even centimeters, often tunneling through the cartilage and ending blindly in the surrounding soft tissue near the temporalis muscle. The depth and tortuosity of this tract are highly variable, which directly impacts the risk of infection.
B. The Hillocks of His: A Developmental Anomaly
The formation of the P.A.S. is traceable to a specific, critical period in early fetal development, typically between the fifth and seventh weeks of gestation. This is when the external ear, or pinna, begins to form.
The auricle develops from six small, distinct mesenchymal swellings that appear around the first branchial cleft (an embryonic groove). These swellings are collectively known as the Hillocks of His, named after the anatomist Wilhelm His.
Hillock Structure Derived Embryonic Arch Origin, 2, 3 Tragus, Crus of Helix, Ascending Helix First Branchial Arch
4, 5, 6 Descending Helix, Antihelix, Antitragus Second Branchial Arch
The eventual shape of the ear depends on the precise, coordinated fusion and migration of these six hillocks. The preauricular sinus forms when the Hillocks of His—specifically the ones derived from the First and Second Branchial Arches—fail to fuse completely or correctly during their merging process. This failure leaves a tiny, residual cleft that closes externally but leaves a shallow tunnel beneath the surface.
This process highlights a core principle of embryology: our final, complex physical structures are built from simpler components that must dissolve or fuse perfectly. The P.A.S. is a minor developmental scar, a fossil record of a process that was almost, but not entirely, complete.
source:Twitter / Kiara Sapinoso
II. Epidemiology, Genetics, and Geographic Variation
A. Global Prevalence Rates
The preauricular sinus is considered a relatively rare trait globally, yet its prevalence varies dramatically across different geographic and ethnic populations, suggesting complex genetic selection or isolation effects:
Geographic Region Estimated Prevalence Observation
