Physiology of Eustachian Tube / Middle Ear / Mastoid

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Physiology of Eustachian Tube / Middle Ear / Mastoid

Otology/Audiology
Author Credentials 

Kathryn Y. Noonan, MD
Neurotology Fellow 
House Clinic 
University of California Los Angeles 
Los Angeles, CA 

 

Module Summary

This module reviews the anatomy and physiology of the middle ear, mastoid, and Eustachian tube.  Understanding the embryology, anatomy, and physiology allows for improved management of Eustachian tube dysfunction and middle ear disease. In depth knowledge of bony middle ear anatomy is necessary when performing surgery in chronic ears because common landmarks may be eroded by disease or absent from previous surgery. Eustachian tube dysfunction can be difficult to diagnose and manage.  Familiarity with clinical and manometric testing may aid in the assessment. 

 

Module Learning Objectives 
  1. Summarize the embryologic development of the middle ear and mastoid.
  2. Identify bony landmarks and spaces in the middle ear and mastoid cavity.
  3. Recognize Eustachian tube anatomy and physiology and how it relates to middle ear disease.
  4. Describe the pathways of gas exchange in the middle ear and mastoid.

 

Embryology

Learning Objectives 
  1. Explain the embryologic origins of the Eustachian tube, middle ear and mastoid. 
  • Tubotympanic recess arising mostly from first pharyngeal pouch
  1. Construct a timeline for embryologic development of the middle ear and mastoid. 
  • Tubotympanic recess formation around 4 weeks 
  • Antrum formation around 22 weeks with continued growth after birth
  • Mastoid formation 34+ weeks with variable development throughout childhood 
  • Mastoid tip development after birth

 

References 
  1. Goeringer GC. Development of the ear. In Lalwani AK and Grundfast KM (eds), Pediatric Otology and Neurotology. J. B. Lippincott Co., Philadelphia, PA, 1998, p 3-10.
  2. Anson BJ, Donaldson JA Surgical Anatomy of the Temporal bone, 3rd edition. Philadelphia, PA: WB Saunders 1981:28.
  3. Wareing MJ, Lalwani, AK, Anwar AA, Jackler RK. Development of the Ear. In Bailey’s Head and Neck Surgery – Otolaryngology Lippincott Co., Philadelphia, PA, 2014, p 2239-2252.

 

Anatomy

Learning Objectives 
  1. Describe the shape, course, and anatomy of the Eustachian Tube including the cartilaginous and bony portions.
  • Relationship to the carotid artery as well as the connection between the middle ear/mastoid and nasopharynx.
  • Know where the ET is narrowest and where it is in closest proximity to the carotid artery.
  1. Identify the bony landmarks in the middle ear and mastoid.
  • Pyramidal eminence, facial ridge, ponticulus, subiculum, cog, promontory, round window, oval window, bony eustachian tube, cochleariform process, semicanal for tensor tympani
  1. Identify spaces in the middle ear and mastoid.
  • Protympanum, epitympanum, mesotympanum, hypotympanum, supratubal recess, posterior tympanic sinus, lateral tympanic sinus, facial recess, antrum, sinus tympani 
  1. Describe the ossicular ligamental attachments and how they influence routes of spread.
References 
  1. Proctor B. Cavities of the Temporal Bone. In: Surgical Anatomy of the Ear and Temporal Bone. New York, NY: Thieme Medical Publishers Inc.; 1989. p. 39-89.
  2. Noonan KY, Linthicum FH, Lopez IA, Ishiyama A, Miller ME. A Histopathologic Comparison of Eustachian Tube Anatomy in Pediatric and Adult Temporal Bones. Otol Neurotol. 2019 Mar;40(3): e233-e239.
  3. Takasaki K, Takahashi H, Miyamoto I, et al. Measurement of angle and length of the eustachian tube on computed tomography using the multiplanar reconstruction technique. Laryngoscope. 2007;117(7):1251-1254.

 

Pathogenesis

Learning Objectives 
  1. Discuss normal Eustachian tube physiology and the mechanism of tubal dilation.
  • Dynamic connection between middle ear and nasopharynx allowing for fluid and gas exchange
  • Levator veli palatine medially rotates cartilage and tensor veli palatine contracts to change convexity and open lumen
  1. Summarize the routes of gas exchange from the middle and mastoid with surrounding areas.
  • Inner ear via round window
  • Ambient atmosphere via tympanic membrane
  • Blood via middle ear mucosa
  • Nasopharynx via the Eustachian tube
  1. Explain the function of mastoid air cells as a buffer in gas exchange and why poor pneumatization is correlated with disease.
  2. Describe the etiology of chronic negative middle ear pressure and how this leads to effusions.
  • Transudate component
  • Exudate component 

 

References 
  1. Proctor B. Cavities of the Temporal Bone. In: Surgical Anatomy of the Ear and Temporal Bone. New York, NY: Thieme Medical Publishers Inc.; 1989. p. 39-89.
  2. Sudhoff HH, Eustachian Tube Dysfunction, Mucosal Gas Exchange, and Effusion. In: The Chronic Ear. New York, NY: Thieme Medical Publishers Inc.; 2016. p. 8-13.

 

Incidence

Learning Objectives 
  1. State the incidence of Eustachian tube dysfunction.
  • Eustachian tube dysfunction in 1% of general population and up to 70% in patient undergoing middle ear surgery

 

References 
  1. Sudhoff HH, Eustachian Tube Dysfunction, Mucosal Gas Exchange, and Effusion. In: The Chronic Ear. New York, NY: Thieme Medical Publishers Inc.; 2016. p. 8-13.

Patient Evaluation

Learning Objectives 
  1. Be familiar with clinical test to evaluate for Eustachian tube dysfunction and discuss the accuracy testing.
  • History
    • ETDQ-7
  • Clinical tests
    • Otoscopy
    • Nasal endoscopy
    • Politzer test
    • Valsalva
    • Toynbee maneuver
  • Manometric test
    • Tympanometry
    • Reflex decay tympanometry
    • Inflation-deflation test
    • Tubomanometry

 

References 
  1. Sudhoff HH, Eustachian Tube Dysfunction, Mucosal Gas Exchange, and Effusion. In: The Chronic Ear. New York, NY: Thieme Medical Publishers Inc.; 2016. p. 8-13.

Imaging

Learning Objectives 
  1. Identify anatomical landmarks in the middle ear and mastoid.
  2. Differentiate between normal anatomy and middle ear pathology based on imaging characteristics.

 

Review

Review Questions 
  1. When does the mastoid tip develop and why is this surgically important?
  2. What is the relationship of the facial nerve to the cochleariform process?
  3. How does pediatric and adult Eustachian tube anatomy differ?
  4. What is the mechanism of Eustachian tube dilation and what muscles are involved?
  5. What are the four routes of middle ear and mastoid gas exchange?
  6. How does the size of the mastoid cavity impact gas exchange?

 

Resources 

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  1. Annual Meeting Webcast (AMW):
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