The Developmental Origin of the Auricula Revisited

Abstract

Objectives/Hypothesis Congenital auricular anomalies are common. Additionally, the auricle plays an important role in the staging of human embryos. However, little is known about the embryological development of the auricle. The most commonly reproduced developmental theory by His (1885) describes six hillocks; three on the first and three on the second pharyngeal arch. The aim of this study was to assess the validity of this theory by modern techniques and to expand the knowledge of the embryological development and morphology of the auricle. Study Design 22 human embryos from the Carnegie collection between Carnegie stage 13 and 23 (28–60 days) were selected based on their histological quality. Methods Histological sections of the selected embryos were examined. Three‐dimensional (3D) reconstructions were prepared. Additionally, literature research was performed. Results The hillocks were absent in most stages. Contrary to common knowledge, the auricle is almost entirely innervated by branches of the facial nerve. The branches of the trigeminal nerve only innervate the tragus and the anterior external auditory meatus (EAM). Consequently, this indicates that almost the entire auricle is derived from the second pharyngeal arch, with the exception of the tragus and the anterior EAM. Conclusions The 3D reconstructions show the anatomy and development of the auricle to be different from concepts presented in current textbooks. As a consequence, we propose that preauricular sinuses should be classified as first pharyngeal arch anomalies. Level of Evidence NA Laryngoscope, 130:2467–2474, 2020

In vitro elastic cartilage reconstruction using human auricular perichondrial chondroprogenitor cell–derived micro 3D spheroids

“…To analyze morphogenesis in early auricular elastic cartilage, we observed the auricular hillocks, which differentiate into auricular cartilage, in E11.5 mouse embryos. 21 – 23 Morphological characteristics, such as a 200–300 μm diameter, round shape, and adjacent positioning, were moderately consistent with those of human auricular hillocks ( Figure 1(b) ). 22 Immunohistochemistry analysis indicated that the auricular hillocks were positive for type I collagen (a broad mesenchymal marker) and SOX9 (a craniofacial chondrogenic and mesenchymal condensation marker) 24 , 25 and negative for type II collagen (a chondrogenic marker).…”

“…[21][22][23] Morphological characteristics, such as a 200-300 μm diameter, round shape, and adjacent positioning, were moderately consistent with those of human auricular hillocks (Figure 1(b)). 22 Immunohistochemistry analysis indicated that the auricular hillocks were positive for type I collagen (a broad mesenchymal marker) and SOX9 (a craniofacial chondrogenic and mesenchymal condensation marker) 24,25 and negative for type II collagen (a chondrogenic marker). These results were consistent with previous reports that the auricular hillocks are the origin of auricular cartilage and that they exhibit a mesenchymal character at this stage (Figure 1(c), Supplemental Video 1).…”

“…The development of the human auricular cartilage begins with the emergence of six round 200-300 μm structures with a mesenchymal character, termed "auricular hillocks," at 6 weeks gestation (Figure 1(a)). [21][22][23] The three anterior hillocks (hillocks 1-3) are derived from the first pharyngeal arch, and the three posterior hillocks (hillocks 4-6) are derived from the second pharyngeal arch; both arches originate from the migrating neural crest cells. The hillocks then fuse together, creating the complex auricle structure.…”

“…The hillocks then fuse together, creating the complex auricle structure. [21][22][23] Previous studies of elastic cartilage tissue engineering have achieved chondrogenic induction by creating macro-level structures. [6][7][8][9][10][11][12][13][14][15] We hypothesized that chondrogenic induction could be improved by mimicking the auricular hillock morphologically, using Φ200-300 μm spheroid culture plates (micro 3D culture).…”

Reduction in postoperative opioid requirement associated with use of the NSS-2® Bridge device, a disposable auriculo-nerve field stimulator, and factors affecting the response in cancer patients undergoing abdominal surgical procedures

“…The ear is uniquely innervated by the branches of the trigeminal, facial, glossopharyngeal, and vagal cranial nerves and the superficial cervical plexus due to its embryological origin [21, 22]. The nuclei of these cranial nerves are located in the brainstem and closely connected to a number of structures, including the tractus solitaries and structures involved in the limbic system such as the thalamus and hypothalamus, amygdala, and rostral ventral medulla [13].…”