Vestibular System Overview and Pathway

Vestibular System Overview

• The vestibular system informs the brain about head position and acceleration.
• The labyrinth, within the inner ear, performs this using two structures:
  • Semicircular canals: Detect angular acceleration. Inertia of endolymph displaces hair cells during angular movement.
  • Otolith organs (utricle and saccule): Detect linear acceleration (gravity). Linear acceleration displaces otoliths, distorting hair cells.

Pathway of Vestibular System

• Vestibular and cochlear nerve fibers travel to the brainstem via the internal auditory meatus.
• Nerve impulses synapse in vestibular nuclei in the brainstem.
• Vestibular nuclei project to:
  • Cerebellum
  • Ocular motor nuclei (control vestibulo-ocular reflexes)
  • Spinal cord (mediating postural reflexes)
  • Thalamus (relay center to the postcentral gyrus)

Vestibular Ocular Reflexes (VOR)

• VOR is mediated by:
  • Vestibular nuclei
  • Medial longitudinal fasciculus (MLF)
  • Oculomotor nuclei (CN III, IV, VI)
• VOR maintains stable gaze during head movement.
• Eyes move in the opposite direction of head movement to maintain fixation.

Tonic Level of Vestibular System Activity

• Vestibular organs consistently send signals, reacting similarly as either active or inactive, based on head movements.
• Asymmetrical input creates a sensory imbalance.
• The brain compensates (likely through the cerebellum) over time.
• Compensation is crucial in the vestibulo-ocular reflex.

Nystagmus

• Involuntary rhythmic oscillation of the eyes, varying in direction (horizontal, vertical, torsional, or mixed).
• Usually includes slow drift and quick jerk movements.
• Direction is named for the fast phase.
• Reflects an imbalance between the semicircular canals or the central nervous system.
• It’s a clinical indicator of issues in the visual, labyrinthine system, cerebellum, or brainstem.

Vertigo

• Sensation of movement of self or environment (often rotational).
• Subjective symptom.
• Accompanied by objective signs (nystagmus).
• Neurovegetative signs (nausea, vomiting).
• Results from a mismatch in primary information systems (visual, vestibular, sensory).

Classification of Vertigo

• Peripheral Vertigo:
  • Benign paroxysmal positional vertigo (BPPV)
  • Vestibular neuritis
  • Ménière's disease
  • Trauma
• Central Vertigo:
  • Vertebrobasilar insufficiency (VBI), transient ischemic attack (TIA), brainstem infarction
  • Tumor or mass
  • Migraine
  • Multiple sclerosis

Specific Peripheral Vertigo Types

• BPPV: Short-lived episodes (minutes), triggered by head movements (often lying down/looking up).
• Vestibular neuritis: A monophasic attack (single occurrence of vertigo) potentially with vomiting, ranging from days to weeks.
• Ménière's disease: Episodes lasting hours, associated with fullness, tinnitus, and/or hearing changes. Frequently triggered by high sodium intake.

Peripheral & Central Vertigo subtypes

• Peripheral Vertigo (continued):
  • Vestibular/acoustic neuroma: Slow-onset, accompanied by hearing loss.
  • Trauma: Injury causing acute, possibly non-vertiginous dizziness.
• Central Vertigo (continued)
• Brainstem infarction: Multiple symptoms including vertigo and other neurological deficits.

Assessment of Vertigo

• Electro/Video nystagmography: Measures eye movements, aiding in assessing saccadic, gaze, and pursuit movements, and head-shake nystagmus.

• Positional nystagmus test: Records eye movements without visual fixation. Tests for positional nystagmus, likely indicative of peripheral vertigo.

• Dix-Hallpike test: Assesses for positional vertigo, often in BPPV.

• Bithermal caloric test: Non-physiologic stimulus via temperature-changed water into the ear to stimulate the vestibular system. Used to diagnose unilateral peripheral vestibular issues.

• Rotating chair test: Assesses vestibulo-ocular reflex (VOR), degree of compensation to movement in central vertigo.

Clinical Vertigo Testing

• Pursuit eye movements: Prevent slipping of an image on the retina, tests the ability of central/peripheral vestibular compensation for eye movement.
• Saccadic tests: Measures voluntary fast eye movements. Crucial for assessing the frontal eye fields, brainstem reticular formation, oculomotor nuclei, and cerebellum, aspects of central and peripheral vestibular compensation.
• Gaze tests: Evaluate the ability to hold a steady gaze without drift or gaze-evoked nystagmus, examining the similarities to saccadic system in central/peripheral vestibular compensation.

Clinical Presentation

• Features of vertigo include duration, description, frequency, potential causes and surrounding symptoms.
• Detailed patterns such as episodic (seconds, minutes, hours, days) or continuous are observed and recorded.

Vertigo Rating Scales

• Scales used to assess the patient's perception of dizziness.

Dizziness Handicap Inventory (DHI)

• Questionnaire evaluating functional/physical/emotional aspects of dizziness and its impact.

This quiz explores the intricate details of the vestibular system, including its structure and function in detecting head position and motion. Test your understanding of how the vestibular system interacts with the brain and other bodily functions, such as reflexes and balance.