Anatomic Dimensions of the Bony External Auditory Canal

Abstract

INTRODUCTION: With increasing numbers of the new generation regularly using high-powered sound technologies but without adequate auditory protection, it is projected that hearing loss will reach record levels in the near future. As such, the hearing aid industry has been, in the past few decades, offering gradually more miniature and lightweight hearing aid technologies. The goal is to meet the current and future demand for patients seeking treatment while preserving a dimension of portability and, if possible, aesthetics. Among the varieties of hearing aids available to patients today, in-the-canal (ITC) and completely-in-the-canal (CIC) devices have received significant attention for their cosmetic appeal.1 In addition to providing a cosmetic effect, these devices also generally provide good auditory function.2-4 Of note, the newest innovation in hearing aid devices, the invisible extended-wear deep-canal device (Lyric®, InSound Medical, Newark, CA), depends entirely on fitting and securing the device in the patient’s external auditory canal (EAC) by an exterior mold.5 Currently, to overcome anatomical variation among different patients, a number of different EAC molds are available for in-clinic test fitting. The human EAC is comprised of two parts – the cartilaginous portion, which is more lateral, and the bony portion, which is more medial. The contours of the bony EAC are reliably visualized using a temporal bone computed tomography (CT) scan.6, 7 To our knowledge, no systematic measurement of anatomic dimensions of the bony and cartilaginous EAC, let alone standardized dimensions for auditory devices that fit into the EAC, has been reported in the literature. In this study, we report a novel method for performing standardized measurements of the bony EAC, as well as average EAC dimensions for 68 patients with special attention to dimensional differences among different age groups. Knowledge of these dimensions may be helpful in guiding surgical procedures or in the design of novel in-the-ear devices (i.e., hearing aids).