Physiology of the Vestibular System

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Physiology of the Vestibular System

Otology/Audiology
Author Credentials 

Syed Ahsan, MD, FACS
Otology/Neurotology, Clinical Asst Professor
Head and Neck Surgery
Kaiser Permanente, Southern California and UC Irvine
Irvine, CA and Orange, CA respectively

 

Module Summary

The peripheral vestibular system develops from the otic placode and interacts with the central vestibular system in order to maintain posture and balance.  The peripheral vestibular system consists of the semicircular canals and the otolith organs (utricle and saccule) involved in detection of angular and linear acceleration/movement, respectively.  The output of the vestibular system are reflexes such as  vestibuloocular reflux, vestibulocolic and vestibulospinal reflexes.  Vestibular hair cells play a role in detecting motion and acceleration.  Balance function depends on the vestibular system interacting with the visual and somatosensory systems.  Deficits can be measured through appropriate physical exam and vestibular testing can help in identifying the ear affected and can help in diagnosis and determining compensation of vestibular function. Understanding the anatomy, embryogenesis, and function of the vestibular system can help in understanding vestibular disorders and help in management of these conditions.

Module Learning Objectives 
  1. Describe the anatomical structures of the inner ear responsible for maintaining balance control and gaze stabilization. 
  2. Explain that the basic function of the vestibular system is gaze stabilization and postural control.
  3. Review the various inputs (vestibular, proprioceptive, visual, auditory) into the brainstem which leads to central processing via interaction with the cerebellum and cerebral cortex which leads to output in form of eye movement and postural control.
  4. Describe Ewald’s Laws and how they can be used to evaluate patients with vestibular disorders. 
  5. Gain an understanding of vestibular tests. 

 

Embryology

Learning Objectives 
  1. Be familiar that the otic placode and vestibular system. 
  2. Describe how the inner ear is derived from the otic placode forming otic vesicle/otocyst. 
  3. Understand the close development of the hindbrain with the developing vestibular –cochlear and facial ganglions. 
  4. Explain the timeline of vestibular embryogenesis.
  5. Cite how timing of insults to the embryo can predict the type of defects of the cochlea and peripheral vestibular system.

 

References 
  1. Peck J. Development of Hearing. Part II. Embryology. J Am Acad Audiol. 1994; 5: 359-365.
  2. Fritzsch B, Barald K, and Lomax M. (1998) Early Embryology of the Vertebrate Ear. In: Rubel EW, Popper AN, Fay RR (eds) Development of the Auditory System. Springer Handbook of Auditory Research. Vol 9. Springer, NY, NY.
  3. Baker R. From genes to behavior in the vestibular system. Otolaryngol Head Neck Surg. 1998; 119: 263-275.
  4. Jackler R, Luxford w, House W. Congenital malformation of the inner ear: a classification based on embryogenesis. Laryngoscope. 1987: 97: 2-14.

 

Anatomy

Learning Objectives 
  1. Review the vestibular structures of the inner ear and how they function (semicircular canals, saccule, utricle) (bony and membranous labyrinth):
  • Understand the function of the ampulated end of the SCCs, which contain the crista and the macula of the otolith organs (saccule and utricle)
  1. Be familiar with Type 1 and Type II hair cells found in the sensory elements of the peripheral vestibular system.
  2. Explain that SCCs are responsible for angular acceleration and the otolith organs are responsible for linear acceleration.
  3. Be familiar with the blood supply to the peripheral vestibular system is via the Labyrinthine artery a branch of AICA.
  4. Describe the vestibular nerve innervations (SVN and IVN).
  5. Gain an understanding of the vestibular nuclei complex. 
  6. Describe the central projections of the vestibular input into the cerebellum, MLF to the cranial nerve, and to the spinal tracts.  Understand which vestibular nuclei are involved in these projections.
  7. Be familiar with vestibular –thalamus and vestibular –hippocampal interactions.
  8. Describe the effects of aging on the vestibular system (the inner ear begins development at 3 weeks of age). 

 

References 
  1. Khan S, Chang R. Anatomy of the vestibular system. A Review. NeuroRehabilitation. 2013; 32: 437-43.
  2. Kingman H, van de Berg R. Anatomy, physiology, and physics of the peripheral vestibular system. Handb Clin Neurol. 2016; 137: 1-6.
  3. Gacek R. Ch3. Anatomy of the Central Vestibular System. In Neurotology. Jackler R, Brackmann D (Eds). 1994. Mosby St. Louis.
  4. Bewley A and Ruckenstein M. Chapter6. Anatomy of the Vestibular System. In Otology and Neurotology. Kirtane M, deSouza C, Sanna M, Devaiah A (Eds). 2013. Thieme, Uttar Pradesh, India.

 

Basic Science

Learning Objectives 
  1. Recognize the function of the semicircular canals and otolith organs in maintaining balance.  
  2. Discuss how damage or disorder of the vestibular system leads to vertigo/dizziness and balance dysfunction.
  3. Understand the basis for caloric testing, vHIT testing, ECOG, rotary chair and VEMP testing.
  4. Describe the mechanism of vestibular compensation after injury. 

 

References 
  1. Tsai B and Lustig L.  Ch. 7. Physiology of the Vestibular system. In Otology and Neurotology. Kirtane M, deSouza C, Sanna M, Devaiah A (Eds). 2013. Thieme, Uttar Pradesh, India.
  2. Tsai B and Lustig L. Ch. 8. Tests to Evaluate the Vestibular System. In Otology and Neurotology. Kirtane M, deSouza C, Sanna M, Devaiah A (Eds). 2013. Thieme, Uttar Pradesh, India.
  3. Goebel J and Sumer B. Ch. 3. Vestibular Physiology. In Clinical Otology. Hughes G, Pensak M. (Eds). 2007. Thieme. New York.
  4. Baloh R, Honrubia V. eds. Clinical Neurophysiology of the Vestibular system. 2nd ed. Philadelphia; FA Davis. 1990.
  5. Curthoys I, Halmagyi G. Vestibular compensation: a review of the oculomotor, neural, and clinical consequences of unilateral vestibular loss. J Vest Res. 1995; 5: 67-107.

 

Genetics

Learning Objectives 
  1. Be familiar with disorders genetic disorders associated with vestibular dysfunction:
  • Usher syndrome, Ménière’s disease, DFNA9
  • Familiar episodic ataxia syndrome Migraine associated dizziness
  1. Be aware of genetic testing for Ushers and DFNA9 is often available.

 

References 
  1. Eppstenier R and Smith R. Genetic disorders of the vestibular system. Curr Opin Otolaryngol Head Neck surg. 2011. 19: 397-402.
  2. Morrison A, Johnson K. Genetics(molecular biology) and Meniere’s disease. Otolaryngol Clin North Am. 2002; 35: 497-516.

 

Measurement of Functional Status

Learning Objectives 
  1. Explain the use of CT scan and MRI in identifying vestibular regions.
  2. Be familiar with identifying cochlear hydrops using MRI. 
  3. Describe function brain imaging of the vestibular system.

 

References 
  1. Held P, Fellner C, Fellner F. et al.  MRI of inner ear anatomy using 3D MP RAGE and 3D CISS sequences. Br. J. Radiol. 1997; 70: 465-472.
  2. Lane JK, Witte RJ, Henson OW et al. Imaging microscopy of the middle and inner ear. Part II: MR microscopy. Clinc Anat. 2005; 18: 409-411.
  3. Shaffer KA, Haughton VM. Thin section computed tomography of the temporal bone. Laryngoscope 1980; 90: 1099-1105.
  4. Tien Rd, Felsberg G, Macfall J. Fast spin-echo high resolution MR imaging of the inner ear. AJR Am J Roentgenol. 1992; 159: 395-8.
  5. Dieterich M, Brandt T. Functional brain imaging of the vestibular system. fMRI and PET. Handbook of clinical Neurophysiology. 2010; 29.

 

Pathology

Learning Objectives 
  1. Define Ewalds law in evaluating patients with dizziness/labyrinthine dysfunction.
  2. Have an understanding of pathophysiology of BPPV – horizontal, posterior and superior canal types.
  3. Explain how labyrinthine dysfunction / injury affects VOR and VSR.
  4. Discuss basis of Ménière’s disease.
  5. Contrast the difference between peripheral and vestibular dysfunction.  

 

References 
  1. Hornibrook J. Benign Paroxysmal Positional Vertigo (BPPV): History, Pathophysiology, Office Treatment and Future Directions. Int J Otolaryngol. 2011; 835671 (online publication).
  2. Epley JM. The Canalith Repositioning Procedure: for treatment of benign paroxysmal positional vertigo. Otolaryngol Head Neck Surg. 1992; 107: 399-404.  
  3. Herdman S. Vestibular Rehabilitation. 2nd Edition. Philadelphia, PA. FA Davis Company. 2000.
  4. Paparella M, Djalilian H. Etiology, pathophysiology of symptoms, and pathogenesis of Meniere’s disease. Otolaryngol Clin North Am 2002; 35: 529-45.

 

Rehabilitation

Learning Objectives 
  1. Explain the anatomical and physiological basis of vestibular compensation. 
References 
  1. Hain, TC. Neurophysiology of vestibular rehabilitation. NeuroRehabilation. 2011; 29: 127-141.
  2. Gans RE. Vestibular rehabilitation therapy. In Dispenza F, De Stefano A (Eds.). Textbook of Vertigo Diagnosis and Management. London, UK Jaypee Brothers Medical Publishers, 2013. 
  3. Herdman S. Vestibular Rehabilitation. 2nd Edition. Philadelphia, PA. FA Davis Company. 2000.

 

Case Studies

  1. A 45 year old woman presents with hearing loss and vertigo.  Examination reveals hearing loss in the left ear and fast beating nystagmus to the right side.  Based on Ewalds 2nd law, the nystagmus should increase when looking towards the direction of fast beating or when looking towards the slow phase?  Caloric testing should show a weakness with cold, warm or both stimulation?  Caloric testing should show weakness on the left side or right side?  vHIT should show a weakness on which side?  After compensation, will the vHIT abnormalities persist or resolve over time?  If the patient continues to have imbalance with activity what would be the next steps in evaluation?  What would be the recommended treatments?

 

  1. A 65 year old man present with positional vertigo lasting less than a minute.  Exam reveals a delayed down beating rotary nystagmus on right hallpike position that lasts for 20 seconds.  What is the best treatment option, Epley maneuver /Canalith positioning maneuver vs. Brandt Daroff Exercises?  After treatment, on recheck with hallpike positioning testing, now the patient shows right side horizontal right beating nystagmus which lasts for 30 seconds.  What is the best treatment option?   On follow-up patient has persistence of positional vertigo c/w BPPV.  What are the treatment options? When is surgery an appropriate option for treatment?  

 

Review

Review Questions 
  1. What are the organs of the peripheral vestibular system and how do they work with one another?  What makes up the central vestibular system?
  2. Define the 3 vestibular reflexes and describe the neural process/structures responsible for them.
  3. Describe the cupula and the macula and how they are arranged. 
  4. Describe the 2 types of vestibular hair cells.  Describe transduction and where in the hair cells does it occur.  What are the stereocilia and kinocilium?  Describe their structure and function.
  5. Describe the neurophysiology of the development of nystagmus.  What differentiates a central cause of nystagmus from peripheral nystagmus?
  6. How does vestibular compensation occur after vestibular injury?
  7. Describe the pathophysiology of Ménière’s disease?
  8. Describe the difference between posterior and horizon BPPV.  What is the difference between canalithiasis vs. cupulolithiasis?

 

References 
  1. Peck J. Development of Hearing. Part II. Embryology. J Am Acad Audiol. 1994; 5: 359-365.
  2. Jackler R, Luxford w, House W. Congenital malformation of the inner ear: a classification based on embryogenesis. Laryngoscope. 1987: 97: 2-14.
  3. Herdman S. Vestibular Rehabilitation. 2nd Edition. Philadelphia, PA. FA Davis Company. 2000.
  4. Khan S, Chang R. Anatomy of the vestibular system. A Review. NeuroRehabilitation. 2013; 32: 437-43.
  5. Goebel J and Sumer B. Ch. 3. Vestibular Physiology. In Clinical       Otology. Hughes G, Pensak M. (Eds). 2007. Thieme. New York.
  6. Baloh R, Honrubia V. Eds. Clinical Neurophysiology of the Vestibular system. 2nd ed. Philadelphia; FA Davis. 1990.
  7. Curthoys I, Halmagyi G. Vestibular compensation: a review of the oculomotor, neural, and clinical consequences of unilateral vestibular loss. J Vest Res. 1995; 5: 67-107.
  8. Hornibrook J. Benign Paroxysmal Positional Vertigo (BPPV): History, Pathophysiology, Office Treatment and Future Directions. Int J Otolaryngol. 2011; 835671 (online publication).

 

Resources 

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