Chapter 14 Ear Reconstruction
INTRODUCTION
Repair of the auricle can be traced back to India (600bce) with subsequent contributions by the Egyptians, Renaissance Italians, nineteenth-century surgeons, and finally German surgeons such as Diffenbach, who played a major role in refining auricle reconstruction.1 Much of the literature has focused on providing a reliable framework either after trauma or for microtia repair. These techniques range from harvesting costal cartilage buried in the abdomen to utilizing porous polyethylene.2
EAR AESTHETICS
While auricle length is somewhat dependent on ethnicity (with African being the shortest and Asian being the longest), the length to width of the auricle should be slightly less than 2:1. Generally, the auricle protrudes from the scalp at a 20°–30° angle.3 A smooth contour outlined by the helical rim and bilateral symmetry are important universal aesthetic norms (Figure 14.1).
The superior aspect of the helical rim, defined by a horizontal line from its attachment to the scalp, needs to maintain a gentle curve without any acute angles. As the rim descends it almost approaches a 90° angle through its mid-portion. The lower third of the auricle curves at approximately a 45° angle as it descends into the earlobe. The lobule has great variability in its length and curvature. Generally, its width is one-third to one-half of the width of the superior portion of the helix. Earlobe length depends on ethnicity, but is approximately 2 cm on average.4 Earlobe thickness or “fleshiness” also varies from barely discernable from the helical rim to a very defined and separate structure. Earlobes tend to be asymmetrical and elongate with age.5 Aesthetically, the most important aspect of the earlobe is its independence as a separate cosmetic unit while maintaining the curved continuity of the helical rim.
EMBRYOLOGY
Embryologically, the ear develops from the first and second branchial arches. These arches arise as hillocks from the neck.6 During the early gestational period, they migrate cephalad. The outline of the ear is apparent early in the fetus at approximately the sixth week. Following birth, the external auricle grows quickly. By the age of 6, it has attained nearly adult size and proportions.
TOPOGRAPHY
With its numerous ridges and valleys designed to improve acoustic reception, the external ear possesses the most complex topography of any cosmetic unit of the head and neck. The auricular framework is formed by cartilage. The earlobe like the nasal alar lobule is made of fibrofatty tissue. The medial-anterior facet of the auricle is characterized by perichondrium and thin skin tightly adherent to cartilage. The posterior-medial aspect has looser skin and some subcutaneous fat overlying the cartilaginous framework (Figure 14.2).
The major anterior landmarks of the external ear are the helix, the scapha, the antihelix, the concha, and the tragus and antitragus. Posteriorly, there are eminences that correspond to these anterior landmarks. Laterally, the helix actually begins with the crus, which originates at the superior aspect of the conchal bowl. The helix extends superiorly in a gentle curve. As it descends, there is a slight prominence known as the Darwinian tubercle. The helix continues its descent uninterrupted to the lobule. Proceeding medially from the helical rim is the scaphoid fossa. This is bounded by superior and inferior crura of the antihelix. As these two limbs of the antihelix stretch to meet the helical rim, a depression known as the triangular fossa bounded by these two limbs and the rim is created. Medially, these ridges bound the concha. This bowl-like structure can be divided into the cymba, which is bounded superiorly by the anterior crus of the antihelix and inferiorly by the crus of the helical rim. Inferior to the crus is the cavum, which has a more concave nature. Although the recessed nature of the concha makes it appear less important to the structure of the auricle, it actually acts as a brace between the mastoid and the remainder of the auricle. Medial-posteriorly, the concha leads to the external auditory canal. Lateral to the canal is the tragus, a roundish prominence. Opposing the tragus, across the conchal valley is the antitragus, a linear prominence at the origin of the antihelix. The posterior aspect of the ear is marked by various ridges and named prominences known as eminences, which correspond to the anterior anatomic landmarks. Aside from the intrinsic rigidity produced by the cartilaginous framework, the auricle is held in placed by small muscles and ligaments. The musculature can be divided into three extrinsic and three intrinsic bands.
Vasculature
The blood supply is mainly supplied by the superficial temporal and the posterior auricular arteries. Both are branches of the external carotid. The superficial temporal artery and its branches, including the direct auricular, supply the anterior (lateral) surface of the ear, particularly the superior half. The posterior auricular artery supplies the entire medial (posterior) surface and has branches that perforate to the opposing surface, mainly supplying the lower half of the ear including the conchal bowl6 (Figure 14.3). Venous drainage occurs via corresponding named veins in addition to the retromandibular vein. These three veins flow into the external jugular vein.
Innervation
The external ear possesses an intricate sensory supply. The innervation is supplied by branches of the cervical nerve, the tenth cranial nerve, the trigeminal nerve, and the lesser occipital nerve. The greater auricular nerve, which originates from C2 and C3, extensively innervates the cranial aspect of the ear including the earlobe. It also branches out to the anterior surface and innervates most of the upper half of the auricle. The auriculotemporal nerve, a branch of V3, supplies the lateral aspect of the superior portion of the helix. The posterior surface of the helix and the eminences of the scapha and fossa triangularis are innervated by the mastoid branch of the lesser occipital nerve. Finally, Arnold’s nerve, a branch of the Vagus (CN10), supplies sensory nerves to the concha.7
RECONSTRUCTIVE OPTIONS
Skin Grafts
Full-thickness skin grafts have a wide application in resurfacing small to medium auricular defects. Grafts will have the highest chance of surviving if there is intact perichondrium. If the wound base consists of cartilage, multiple full-thickness perforations of the cartilage with a 2-mm punch can be used to facilitate the blood supply.8 Common donor areas include the pre- and postauricular sulci. The postauricular region is desirable since the scar will be hidden and it can heal by second intent or be closed primarily (Figure 14.4). The preauricular region may provide a slightly thicker graft. This site is a good choice when there are significant creases in which to hide the scar. It is rare that this donor site is left to heal by second intention. Generally, the donor site is from the ipsilateral side since this will decrease the need for patient repositioning.