Downloaded from http://journals.lww.com/otology-neurotology by BhDMf5ePHKbH4TTImqenVM+rzkOt3HMmGkO/p3Xqz4V5LfxDTh1iAPpyeKKFAuLg on 07/03/2020 Copyright © 2020 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited. Original Study Age as a Factor of Growth in Mastoid Thickness and Skull Width  Fida Abdulaziz Almuhawas, yAnandhan E. Dhanasingh, yDijana Mitrovic, zYassin Abdelsamad,  Farid Alzhrani,  Abdulrahman Hagr, and  Abdulrahman Al Sanosi  Department of Otolaryngology, King Abdullah Ear Specialist Center (KAESC), King Saud University, Riyadh, Saudi Arabia; yResearch and Development, MED-EL, Innsbruck, Austria; and zResearch Department, MED-EL, Riyadh, Saudi Arabia Objectives: To understand the growth rate of mastoid thickness and skull width associated with the age for both normal and malformed inner-ear anatomy groups. Also, to determine if there is any mathematical relation between cochlear size as measured by the ‘‘A’’ value against the age, mastoid thickness, and skull width. Methods: Ninety-two computed tomography image datasets of human temporal bone were made available that contained normal (n ¼ 44) and malformed inner-ear (n ¼ 48) anatomies. The age of the subjects ranged from 6 months to 79 years. CE marked OTOPLAN preplanning otology software was used to load the patient’s preoperative images for making all the measurements including mastoid thickness, skull width, and the cochlear size as measured by the ‘‘A’’ value. Mastoid thickness was measured both in axial and coronal planes starting from the cochlear entrance to the skull surface, with the line in plane with the basal turn of the cochlea. Skull width was measured from side to side in both axial and coronal planes from the image slice that gave the highest width. The cochlear size in terms of basal turn diameter ‘‘A’’ was measured from ‘‘Cochlear View’’ in the oblique coronal plane. Results: Mastoid thickness and skull width increased with age in a logarithmic manner. The mastoid thickness increased from a minimum of 17 mm to around 34 mm and the skull width increased from 105 mm to around 146 mm as the age increased from 6 months to 20 years. At the age of around 20, both the mastoid thickness and skull width reached the plateau and thereafter with a very little growth. The skull width was linearly correlated with the mastoid thickness conveying the fact that bigger the head size is, thicker will be the mastoid. The size of the cochlea as measured by the ‘‘A’’ value did not have any meaningful correlation with the age, mastoid thickness, and skull width. This conveys the message that the cochlear size is indepen- dent of the overall size of head and the age of patient. Conclusions: Mastoid thickness and skull width increased with age, while the cochlear size was independent of age, mastoid thickness, and the size of the skull. Key Words: Age of patients—Cochlear size—Mastoid thickness—Skull width. Otol Neurotol 41:709–714, 2020. Surgical placement of Cochlear Implant (CI) involves significant amount of drilling in the mastoid portion of temporal bone to reach the inner-ear through facial nerve recess (1). The CI electrode-lead coming from the implant stimulator is then routed through the mastoid drilled cavity through the facial recess to reach the cochlea. The excess electrode lead is coiled in the mastoid cavity and is expected to un-coil accommodating the natural growth in the mastoid with age. A good understanding on the rate of mastoid and skull growth over age would be interesting for the CI surgeons, especially dealing with pediatrics as the CI surgery is considered safe even from the age of 6 months as it has been reported by (2). The aim of this study is to understand how the mastoid thickness (skull surface to the cochlear entrance) and skull width grow in different age groups in both normal and malformed inner-ear anatomies. The results could be a good reference especially for the junior CI surgeons in knowing how deep the mastoid needs to be drilled to reach the cochlea in different age-group patients. Also this would be interesting for the CI companies to design their excess electrode lead length for the future genera- tion of implants. METHODS Subject Demographics Computed tomography (CT) image datasets of 92 subjects with both normal (n ¼ 44) and malformed inner-ear anatomies Address correspondence and reprint requests to Fida Abdulaziz Almuhawas, Department of Otolaryngology, King Abdullah Ear Spe- cialist Center (KAESC), King Saud University, PO Box 245 Riyadh 11411, Saudi Arabia; E-mail: fmuhawas@ksu.edu.sa; Dr. Anandhan E. Dhanasingh, Research and Development, MED-EL, Innsbruck, Austria; E-mail: Anandhan.dhanasingh@medel.com F.A.A. and A.E.D. have equal contribution. Asst. Prof. Dr. F.A.A., Associate Prof. Dr. F.A., Prof. Dr. A.H., and Prof. Dr. A.A.S. are employed by King Abdullah Ear Specialist Center, King Saud University, Riyadh, Saudi Arabia. Dr. A.E.D., Ms. D.M., and Dr. Y.A. are employed by MED-EL GmbH and they all have scientific roles with no marketing activities. The authors disclose no conflicts of interest. DOI: 10.1097/MAO.0000000000002585 ß 2020, Otology & Neurotology, Inc.