Preauricular sinuses are common congenital malformations first described by Heusinger in 1864. Preauricular sinuses are frequently noted on routine physical examination as small dells adjacent to the external ear, usually at the anterior margin of the ascending limb of the helix. However, preauricular sinuses have been reported to occur along the lateral surface of the helicine crus and the superior posterior margin of the helix, the tragus, or the lobule. Anatomically, preauricular sinuses are lateral and superior to the facial nerve and the parotid gland.
Preauricular sinuses are inherited in an incomplete autosomal dominant pattern, with reduced penetrance and variable power of expression. They can arise spontaneously. The sinus may be bilateral in 25-50% of cases, and bilateral sinuses are more likely to be hereditary.  In unilateral cases, the left side is more commonly affected.
Also see the related article Preauricular Cysts, Pits, and Fissures.
During embryogenesis, the auricle arises from the first and second branchial arches during the sixth week of gestation. Branchial arches are mesodermal structures covered by ectoderm and lined with endoderm. These arches are separated from each other by ectodermal branchial clefts externally and by endodermal pharyngeal pouches internally. The first and second branchial arches each give rise to 3 hillocks; these structures are called the hillocks of His. Three hillocks arise from the caudal border of the first branchial arch, and 3 arise from the cephalic border of the second branchial arch. These hillocks should unite during the next few weeks of embryogenesis. Preauricular sinuses are thought to occur as a result of incomplete fusion of these hillocks.
Preauricular sinuses are usually narrow, they vary in length (usually they are short), and their orifices are usually minute. They may arborize and follow a tortuous course in the immediate vicinity of the external ear. The preauricular sinuses are usually found lateral, superior, and posterior to the facial nerve and the parotid gland. In almost all cases, the duct connects to the perichondrium of the auricular cartilage. They can extend into the parotid gland.
Congenital periauricular fistulas may be seen as variations of preauricular sinuses. 
In one study, the incidence of preauricular sinuses in the United States is estimated to be 0-0.9% and the incidence in New York State is estimated to be 0.23%.
In Taiwan, the incidence of preauricular sinuses is estimated to be 1.6-2.5%; in Scotland, 0.06%; and in Hungary, 0.47%. In some parts of Asia and Africa, the incidence of preauricular sinuses is estimated to be 4-10%. One study in Kenya found preauricular sinuses to be the most common congenital oral and craniofacial anomalies, with a rate of 4.3 cases per 1000 persons. 
The incidence of preauricular sinuses in whites is 0.0-0.6%, and the incidence of preauricular sinuses in African Americans and Asians is 1-10%.
Both men and women are affected equally by preauricular sinuses.
Preauricular sinuses arise in the antenatal period and are usually present at birth, but they can become apparent later in life.
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