Glossary

Concise definitions of the vocabulary used throughout the atlas. Search by term or by definition keyword.

36 entries

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Alexander's law: The intensity of peripheral spontaneous nystagmus increases on gaze toward the direction of the fast phase, decreases on gaze toward the slow phase. A reliable feature of peripheral vestibular nystagmus.
Ampullofugal: Endolymph flow away from the ampulla. In the vertical canals, this is the more potent excitatory stimulus.
Ampullopetal: Endolymph flow toward the ampulla. In the horizontal canal, this is the more potent excitatory stimulus.
Apogeotropic: Beating away from the ground. In horizontal-canal BPPV, apogeotropic nystagmus indicates cupulolithiasis; the weaker side is the affected ear.
AVS: Acute vestibular syndrome — rapid-onset vertigo lasting days, nausea/vomiting, gait unsteadiness, head-motion intolerance, and spontaneous nystagmus. The setting in which HINTS applies.

Bárány Society criteria: Consensus diagnostic criteria for vestibular disorders published by the Bárány Society — including vestibular migraine, PPPD, BPPV variants, and Ménière's. The current standard for classification.
BPPV: Benign paroxysmal positional vertigo. Brief episodic vertigo triggered by head position changes, caused by dislodged otoconia in a semicircular canal. Posterior canal involved in ~85% of cases.

Canalithiasis: Free-floating otoconia in the lumen of a semicircular canal. Produces brief, fatigable, latency-onset positional nystagmus. The common form of BPPV.
Cupulolithiasis: Otoconia adherent to the cupula, making it gravity-sensitive. Produces persistent, non-fatigable positional nystagmus. Apogeotropic horizontal-canal BPPV is the classic example.
CVS: Chronic vestibular syndrome — persistent dizziness over weeks to months, often without discrete attacks. Bedside exam frequently normal; diagnosis rests on history pattern, vestibular function testing, and exclusion. Includes PPPD, bilateral vestibulopathy, cerebellar degeneration, and mal de débarquement syndrome.

Dix-Hallpike: Diagnostic positional maneuver for posterior (and anterior) canal BPPV. Patient is rapidly moved from sitting to head-hanging supine with head turned 45° to the test side.

Epley maneuver: Canalith repositioning procedure for posterior canal BPPV. Sequential head positions move debris out of the posterior canal back to the utricle. ~80% efficacy on first attempt.
Ewald's laws: Three rules: (1) nystagmus from a canal occurs in the plane of that canal; (2) in the horizontal canal, ampullopetal flow is more excitatory than ampullofugal; (3) in vertical canals, ampullofugal flow is more excitatory.

Frenzel lenses: High-magnification (+20D) goggles that prevent visual fixation while allowing the examiner to see the patient's eyes. Used to unmask peripheral nystagmus that would otherwise be suppressed by fixation.

Geotropic: Beating toward the ground. In horizontal-canal BPPV, geotropic nystagmus indicates canalithiasis; the stronger side is the affected ear (Ewald's first law).

Hennebert sign: Vertigo and nystagmus triggered by pressure changes in the ear canal (e.g., tragal pressure or Valsalva). Suggests a 'third window' such as superior canal dehiscence or perilymph fistula.
HINTS: Head Impulse + Nystagmus + Test of Skew. A 3-step bedside exam for the acute vestibular syndrome that distinguishes peripheral (benign) from central (dangerous) causes. Sensitivity for stroke approaches 100% in trained hands, exceeding early MRI-DWI.
HINTS+: Standard HINTS plus a finger-rub hearing test. Unilateral hearing loss in acute vestibular syndrome with otherwise 'benign' HINTS pattern raises suspicion for AICA stroke (since the labyrinth is supplied by the AICA-derived internal auditory artery).

INO: Internuclear ophthalmoplegia. Lesion of the medial longitudinal fasciculus producing slow/incomplete adduction on the side of the lesion with dissociated abducting nystagmus of the contralateral eye. Bilateral INO in someone <40 = MS until proven otherwise.

MdDS: Mal de débarquement syndrome — persistent sensation of rocking or swaying lasting >1 month after exposure to passive motion (cruise, long flight, train). The illusory motion characteristically improves with re-exposure to passive motion (re-driving). Falls in the CVS bin.
MLF: Medial longitudinal fasciculus. A brainstem white-matter tract connecting the abducens nucleus on one side to the contralateral oculomotor nucleus, coordinating horizontal conjugate gaze. Lesions cause INO.

Neural integrator: The brainstem-cerebellar circuit that mathematically integrates eye-velocity commands into the tonic position signal needed to hold eccentric gaze. Horizontal integrator: nucleus prepositus hypoglossi + medial vestibular nucleus. A 'leaky' integrator produces gaze-evoked nystagmus.

OKN: Optokinetic nystagmus. A reflexive jerk nystagmus produced by a moving full-field visual stimulus. Slow phase tracks the stimulus, fast phase resets. Tests the cortico-subcortical visual-motor pathway.

PPPD: Persistent postural-perceptual dizziness. A functional vestibular disorder defined by Bárány Society 2017 criteria: ≥3 months of dizziness/unsteadiness exacerbated by upright posture, motion, and complex visual stimuli, typically after a precipitating vestibular event.
PPRF: Paramedian pontine reticular formation. Brainstem generator of horizontal saccades — contains the excitatory burst neurons that drive the ipsilateral abducens nucleus.

riMLF: Rostral interstitial nucleus of the medial longitudinal fasciculus. Midbrain generator of vertical and torsional saccades.

Saccade: Rapid (≤100 ms), ballistic eye movement bringing a peripheral target onto the fovea. Velocities up to 700°/s. Generated by the brainstem burst neurons (PPRF for horizontal; riMLF for vertical).
Skew deviation: Vertical ocular misalignment from disruption of the utricle-to-riMLF otolith-ocular pathway. A central sign in the acute vestibular syndrome (the 'S' in HINTS).
Smooth pursuit: Continuous low-velocity eye movement tracking a moving target. Saturates ~50°/s. Saccadic ('cogwheel') pursuit suggests cerebellar disease, drug toxicity, or simply age and inattention.
SSCD: Superior semicircular canal dehiscence. A bony defect in the roof of the superior canal creates a 'third window' in the labyrinth, producing sound- and pressure-induced vertigo (Tullio, Hennebert) plus autophony of internal body sounds.

TiTrATE: A framework for the dizzy patient that sorts presentations by Timing (acute / episodic / chronic), Triggers (spontaneous / triggered), and Targeted Exam findings. Four vestibular syndromes fall out: AVS, episodic spontaneous, episodic triggered, and CVS.
Tullio phenomenon: Vertigo and nystagmus triggered by loud sound. Classic for superior canal dehiscence; also seen in some perilymph fistulas and advanced Ménière's.

VEMPs: Vestibular evoked myogenic potentials. Cervical VEMP (cVEMP) tests the saccule via the inferior vestibular nerve; ocular VEMP (oVEMP) tests the utricle via the superior vestibular nerve. Lowered cVEMP thresholds + elevated oVEMP amplitudes characterize superior canal dehiscence.
vHIT: Video head impulse test. Records eye and head velocity during rapid passive head turns to measure VOR gain (eye velocity / head velocity) for each semicircular canal. Detects covert catch-up saccades invisible at bedside.
VOR: Vestibulo-ocular reflex. Three-neuron arc from semicircular canal afferents → vestibular nucleus → ocular motor neurons, producing compensatory eye movements during head motion. Latency ~7 ms — the fastest reflex in the body.

Wallenberg syndrome: Lateral medullary infarction (usually PICA). Ipsilateral Horner's, facial hypalgesia, dysphagia, dysarthria, hoarseness, ataxia; contralateral body hypalgesia. May present as acute vestibular syndrome.