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Microtia

Table of Contents

Introduction

Congenital malformation of external ear

“Micro” = small

“Otia” = ear

Background

Epidemiology

  • Ear deformity in 1.1% of births
  • Incidence of microtia = 1/7000-8000 births
  • Male predominance
    • Male:Female = 2-3:1
  • Right side predominance
    • Right side = 60%
    • Left side = 30%
    • Bilateral = 10%
  • Ethnic distribution
    • Hispanic
    • Asian
    • Pima Indians: incidence = 1/70

Embryology

External ear

  • Development occurs during weeks 4 to 8 of gestation
    • 1st and 2nd branchial arches, clefts and pouches contribute to development of external and middle ear
  • Auricle or pinna
    • Develops from 6 mesodermal thickenings (called hillocks) that derive from 1st and 2nd branchial arches 
      • Development begins during gestational weeks 3 to 6
      • Pinna completely formed by week 16 
    • 1st (mandibular) arch → 3 hillocks
      • Becomes superior helix and tragus
    • 2nd (hyoid) arch → 3 hillocks
      • Becomes antitragus, antihelix, lobule
    • Hillocks encircle first pharyngeal cleft
    • Hillocks fuse

Inner Ear

  • Development begins prior to middle or external ear
  • Develop separately from external ear from otic placodes
    • Otic placodes develop into otic pits and then into otic vesicles
    • Otic vesicles are primordial inner auditory and vestibular systems

Anatomy

Typical Ear Measurements

  • Vertical height of ear = between orbital rim and helical root 
    • Usually 5 to 6 cm
  • Ear width = 55% of ear length 
  • Helical rim 
    • Protrudes 1 to 2 cm from s

Etiology & Pathophysiology