Glossary

A syndromic presentation of sudden continuous vertigo lasting more than 24 hours, with nausea, gait imbalance, and intolerance of head movement. The differential is broad — peripheral causes (vestibular neuritis) versus central causes (posterior circulation stroke) — and is resolved bedside by the HINTS examination.

Branch of the basilar artery supplying the anterior-inferior cerebellum, lateral pontomedullary brainstem, and — via the labyrinthine artery — the inner ear. AICA infarction can mimic peripheral vestibular neuritis because the labyrinth is involved, but bedside hearing testing (HINTS-Plus) detects the additional cochlear infarction.

Difference between air-conduction and bone-conduction thresholds at a given frequency. A gap ≥ 10 dB indicates a conductive component. Low-frequency air-bone gaps occur in otosclerosis but also in third-window pathologies such as SCDS (where the gap is pseudo-conductive).

Chronic toxic ataxia from prolonged heavy alcohol use. Anterior-vermis-predominant atrophy producing gait ataxia with relatively preserved limb coordination. Originally described by Victor and Adams in 1959 as a distinct entity from Wernicke-Korsakoff syndrome. Modern data implicate concurrent nutritional deficiency and gluten sensitivity as contributors.

Empirical observation that horizontal peripheral vestibular nystagmus increases in amplitude when the patient looks in the direction of the fast phase, and decreases when looking in the opposite direction. Used at the bedside as one feature suggesting a peripheral rather than central origin.

The dilated end of each semicircular canal containing the crista ampullaris — the sensory epithelium with hair cells that detect angular acceleration. The cupula sits on the crista and is deflected by endolymph flow.

Positional nystagmus that beats AWAY from the ground (away from the down-side ear during the supine roll test). Seen in horizontal canal cupulolithiasis or, when persistent and central in character, in cerebellar lesions.

Graphical record of hearing thresholds at each frequency, measured separately for each ear. Air-conduction (headphone) thresholds use ◯ for right and ✕ for left; bone-conduction (bone oscillator) thresholds use ⊏ and ⊐. The shape, symmetry, and air-bone gap are diagnostic.

Abnormal perception of one's own voice as louder, hollow, or echoing in the affected ear — and in florid cases, perception of one's own bodily sounds (eyeballs moving, footsteps, heartbeat). A cardinal symptom of superior canal dehiscence and other third-window disorders.

International society for neurootology that publishes the consensus diagnostic criteria for most vestibular disorders, including BPPV (2015), Ménière's (2015 with AAO-HNS), vestibular migraine (2012 with IHS), SCDS (2021), vestibular neuritis (2022), and PPPD (2017).

The most common cause of vertigo. Brief episodes of vertigo (seconds, sometimes up to a minute) triggered by specific head positions, caused by free-floating otoconia in a semicircular canal (canalithiasis) or rarely attached to the cupula (cupulolithiasis). Most commonly involves the posterior canal.

Bedside or laboratory test of horizontal semicircular canal function by irrigating the external auditory canal with warm or cool air/water, which induces an endolymph current and nystagmus. Asymmetric responses (canal paresis) localise vestibular hypofunction; absent responses on one side suggest superior division neuritis or a profound peripheral lesion.

Mechanism of BPPV in which otoconia float freely within the semicircular canal lumen. Head movements cause gravity-driven movement of the particles, producing endolymph flow and cupular deflection — and consequently brief vertigo. Canalithiasis is the substrate the Epley manoeuvre treats.

Characteristic dip in bone-conduction thresholds (typically 5–15 dB at 2 kHz) seen in otosclerosis. The notch is not a true sensorineural loss — it reflects the impact of stapedial fixation on inner-ear mechanics. Helpful in distinguishing otosclerosis from SCDS, where bone conduction at 2 kHz is normal or supranormal.

HINTS pattern indicating a central rather than peripheral cause of acute vestibular syndrome: any one of normal head impulse, direction-changing nystagmus, or skew deviation. Properly performed, has higher sensitivity for stroke than early MRI within 24 hours of symptom onset.

Cluster of executive, visuospatial, linguistic, and affective disturbances first described by Schmahmann and Sherman in 1998 in patients with cerebellar lesions. Frequently the most disabling aspect of cerebellar pathology and frequently missed when attention focuses on motor signs. Screened with the CCAS scale.

The phylogenetically newest cerebellar zone — the lateral hemispheres — that handles motor planning and contributes to cognitive and affective processing. Lesions produce ipsilateral limb dysmetria, dysarthria, and the cerebellar cognitive-affective syndrome (CCAS).

Hearing loss caused by impaired sound transmission through the outer or middle ear, producing an air-bone gap on audiometry with normal bone conduction. Causes include cerumen impaction, tympanic membrane perforation, ossicular discontinuity, otosclerosis, and effusion. SCDS produces a pseudo-conductive pattern with SUPRANORMAL bone conduction.

Sensory epithelium within each semicircular canal ampulla, containing hair cells with stereocilia that project into the gelatinous cupula. Detects angular acceleration via cupular deflection.

Gelatinous mass sitting on the crista ampullaris of each semicircular canal. Has the same specific gravity as endolymph, so it deflects with endolymph flow during angular head movement but is not affected by gravity in the resting state. Cupulolithiasis (otoconia stuck to the cupula) makes it gravity-sensitive, producing persistent positional symptoms.

Mechanism of BPPV in which otoconia adhere to the cupula rather than floating in the canal lumen, making the cupula gravity-sensitive. Produces longer-duration positional nystagmus (>60 seconds) than canalithiasis, and apogeotropic direction in the horizontal-canal variant.

Vestibular-evoked myogenic potential recorded from the sternocleidomastoid muscle in response to loud acoustic stimulation. Measures the saccular–inferior vestibular nerve–vestibulospinal pathway. Absent in selective inferior-division neuritis; enhanced (lowered threshold, increased amplitude) in SCDS.

Nystagmus that changes direction depending on eye position — e.g. left-beating on left gaze and right-beating on right gaze. A central sign in the HINTS examination, suggesting cerebellar or brainstem pathology rather than peripheral vestibular hypofunction.

Diagnostic positional manoeuvre for posterior canal BPPV. With the patient sitting, the head is turned 45° to one side, then rapidly laid supine with the head extended 20° below the horizontal. A positive test elicits upbeating-torsional nystagmus (toward the dependent ear) with characteristic latency and crescendo-decrescendo pattern.

Vertical nystagmus with the fast phase beating downwards, typically maximal on lateral and downward gaze. Pathognomonic of central pathology — most often localising to the cervicomedullary junction or the vestibulocerebellum (Chiari malformation, demyelination, drug toxicity).

High-potassium fluid filling the membranous labyrinth. Movement of endolymph during head motion deflects the cupula or otoconial membrane, opening hair-cell mechanotransduction channels. Endolymphatic hydrops — abnormal expansion of endolymphatic spaces — is the underlying mechanism of Ménière's disease.

Abnormal dilatation of endolymphatic spaces, accepted as the histopathological substrate of Ménière's disease. Hydrops can be confirmed in vivo on delayed gadolinium MRI of the inner ear. Hydrops is necessary but possibly not sufficient — asymptomatic hydrops has been documented histologically.

Treatment manoeuvre for posterior canal BPPV (Epley 1992). Five sequential positions, each held for 30–60 seconds, designed to move otoconia from the posterior canal back into the utricle. Single-treatment success ~70–80%, rising to ~90% after a second visit.

Application of pressure to the external auditory canal (positive or negative, via pneumatic otoscope or tragal pressure) to test for an abnormal communication between the middle ear and the inner ear. A positive test — vertigo and/or eye movement — suggests perilymph fistula, SCDS, or labyrinthine fistula from cholesteatoma.

Autosomal-recessive cerebellar ataxia caused by GAA-repeat expansion in the frataxin gene. Onset first to second decade. Phenotype: progressive ataxia with areflexia, Babinski sign, cardiomyopathy, and diabetes. The Harding 1981 criteria define the classical phenotype.

Nystagmus that appears or worsens on eccentric gaze, with the fast phase beating in the direction of gaze. Common in cerebellar or brainstem pathology (multiple sclerosis, drugs like phenytoin), or with neuromuscular causes of gaze-holding failure.

Positional nystagmus that beats TOWARDS the ground (towards the down-side ear during the supine roll test). The geotropic pattern is characteristic of horizontal canal canalithiasis; the affected side is the side where the nystagmus is more intense.

Immune-mediated cerebellar ataxia in patients with gluten sensitivity, mediated by anti-transglutaminase-6 (anti-TG6) and anti-gliadin antibodies. May respond to gluten-free diet in some cases. Often without overt gastrointestinal disease.

Mechanosensory cell in the inner ear that converts mechanical movement (cochlear basilar membrane displacement, or vestibular cupular/otoconial membrane deflection) into a receptor potential. Vestibular hair cells have a single kinocilium and a graded array of stereocilia; deflection toward the kinocilium depolarises the cell.

Bedside test of the angular vestibulo-ocular reflex (VOR). With the patient fixating a target, the examiner makes a small, rapid, unpredictable head turn. A normal VOR keeps the eyes locked on the target; a hypofunctioning vestibular nerve produces a corrective catch-up saccade — the diagnostic positive sign of peripheral vestibular loss.

Pressure-induced vertigo or eye movement — provoked by tragal pressure, pneumatic otoscopy, or Valsalva. A feature of third-window disorders (SCDS), perilymph fistula, and labyrinthine fistula from cholesteatoma. Hennebert in the absence of middle-ear disease is highly suggestive of SCDS.

Three-step bedside examination for acute vestibular syndrome. Properly performed within 24 hours of symptom onset, HINTS has 100% sensitivity and 96% specificity for central cause (Kattah 2009) — outperforming early MRI. Components: head impulse test, nystagmus character, and test of skew. Any one central feature suggests stroke.

HINTS plus bedside hearing testing. Adds sensitivity for AICA infarction, which can produce an abnormal head impulse (from labyrinthine artery involvement) and look peripheral on standard HINTS — but adds acute unilateral hearing loss as a discriminator.

Variant of BPPV affecting the horizontal (lateral) semicircular canal. Diagnosed on the supine roll test (not Dix-Hallpike). Produces horizontal positional nystagmus — geotropic if canalithiasis, apogeotropic if cupulolithiasis. Treated with the Lempert (barbecue) roll or Gufoni manoeuvre.

Inferior division of the vestibular nerve, carrying afferents from the posterior semicircular canal and the saccule. Less commonly affected in vestibular neuritis (~5–15% of cases), but selective inferior-division neuritis produces a distinctive pattern: normal head impulse, normal caloric, but absent cVEMP.

Bony canal in the petrous temporal bone transmitting the facial nerve, the cochlear nerve, and the two divisions of the vestibular nerve from the cerebellopontine angle to the inner ear. The site at which most vestibular schwannomas arise; MRI of the IAC with gadolinium is the gold-standard imaging.

Failure of conjugate horizontal gaze caused by a lesion of the medial longitudinal fasciculus (MLF) — the ipsilateral eye fails to adduct on lateral gaze, with abducting nystagmus in the contralateral eye. Convergence is preserved (the diagnostic discriminator from a third-nerve lesion). Bilateral INO in a young patient strongly suggests MS.

Terminal branch of AICA supplying the inner ear (cochlea and labyrinth). Acute labyrinthine artery infarction causes simultaneous sudden hearing loss and vertigo — the hallmark of AICA stroke, captured by the hearing component of HINTS-Plus.

Sensory epithelium of the otolith organs (saccule and utricle). Hair cells in the macula project stereocilia into the otoconial membrane, which is loaded with calcium carbonate otoconia. Linear acceleration and gravity deflect the membrane, deflecting the hair-cell bundles.

White-matter tract in the brainstem that connects the abducens nucleus (pons) with the contralateral oculomotor nucleus (midbrain), yoking the lateral rectus to the contralateral medial rectus during conjugate horizontal gaze. Demyelination produces INO; bilateral MLF involvement produces bilateral INO (WEBINO).

Inner-ear disorder characterised by recurrent attacks of vertigo (20 min–12 h) with fluctuating low-frequency sensorineural hearing loss, tinnitus, and aural fullness — the 2015 Bárány/AAO-HNS definite criteria. Histopathological substrate is endolymphatic hydrops.

Demyelinating disease of the central nervous system. Vestibular manifestations include INO, gaze-evoked nystagmus, downbeat nystagmus, periodic alternating nystagmus, and cerebellar ataxia. Diagnosis follows the McDonald criteria — most recent revision 2024 (Montalbán et al.) recognises the optic nerve as a fifth topographic site for DIS.

Involuntary rhythmic eye movement with a slow and a fast phase. Direction conventionally named after the fast phase. Pattern (horizontal/vertical/torsional, unidirectional/direction-changing, fixation-suppressed or not, gaze-evoked, positional) localises the lesion and distinguishes peripheral from central pathology.

Back-to-back conjugate saccades occurring in all directions without an intersaccadic interval — a pathological extension of ocular flutter. In children classically signals neuroblastoma (opsoclonus-myoclonus-ataxia syndrome); in adults usually indicates paraneoplastic syndromes or post-infectious encephalitis. Often coexists with square-wave jerks and ocular flutter.

Calcium carbonate crystals embedded in the otoconial membrane overlying the saccular and utricular maculae. Their density makes the otolith organs gravity-sensitive. Displaced otoconia drifting into a semicircular canal cause BPPV (canalithiasis).

Bony otic capsule disease, most commonly causing stapedial fixation and a low-frequency conductive hearing loss with a Carhart notch at 2 kHz. Acoustic reflexes are absent on the affected side. The diagnostic look-alike for SCDS — preserved acoustic reflexes and supranormal bone conduction distinguish SCDS from otosclerosis.

Vestibular-evoked myogenic potential recorded from the inferior oblique muscle (just below the eye) in response to acoustic or vibratory stimulation. Measures the utricle–superior vestibular nerve–ocular reflex. Reduced or absent in superior vestibular neuritis; enhanced in SCDS.

Immune-mediated subacute cerebellar syndrome triggered by an underlying (often occult) cancer. Anti-Yo (ovarian, breast), anti-Hu (small-cell lung), anti-Tr (Hodgkin), and anti-Ri (breast, lung) are the canonical antibodies. The neurological syndrome frequently precedes the cancer diagnosis. PNS-Care 2021 criteria standardise diagnosis.

High-sodium fluid filling the bony labyrinth between the endolymph and the periosteum. Perilymph and endolymph are separated by the membranous labyrinth. A communication between perilymph and the middle ear is a perilymph fistula.

Abnormal communication between the perilymph-filled inner ear and the middle ear, typically at the oval or round window. Causes fluctuating sensorineural hearing loss and vertigo, often triggered by barotrauma, head injury, or surgery. Cochlin-tomoprotein (CTP) is a perilymph-specific biomarker with ~95% specificity in confirmed cases.

Horizontal nystagmus that changes direction every 90–120 seconds — right-beating for two minutes, briefly null, then left-beating for two minutes, and so on. Pathognomonic of nodular (vestibulocerebellar) pathology. Suppressed by baclofen, which is the established symptomatic treatment.

HINTS pattern indicating peripheral rather than central cause: abnormal head impulse on the affected side, unidirectional fixation-suppressed nystagmus, and no skew. Sensitivity 100% and specificity 96% for peripheral cause when all three components agree.

Ischaemic stroke in the vertebrobasilar territory — affecting the brainstem, cerebellum, posterior cerebral hemispheres, or terminal branches such as the labyrinthine artery. May present with isolated vertigo. DWI MRI has 80–88% sensitivity within the first 48 hours; the HINTS examination outperforms early MRI for central vs peripheral discrimination.

Chronic functional vestibular disorder. Symptoms (dizziness, unsteadiness, or non-spinning vertigo) on ≥15 days per month for ≥3 months, exacerbated by upright posture, motion, and complex visual stimuli — all three required by Bárány 2017 criteria. Treatment: CBT, vestibular rehabilitation, and SSRIs.

One of the two otolith organs in the vestibule, oriented vertically. Detects linear acceleration in the sagittal plane and gravity. Innervated by the inferior vestibular nerve; saccular function is tested with the cVEMP.

Third-window disorder caused by absent bone over the superior semicircular canal. Sound and pressure stimuli are abnormally transmitted into the labyrinth, producing the clinical triad of autophony, Tullio phenomenon, and Hennebert sign. Audiogram shows low-frequency air-bone gap with supranormal bone conduction. Bárány Society 2021 diagnostic criteria.

One of three fluid-filled canals in each labyrinth — anterior (superior), posterior, and lateral (horizontal) — oriented at right angles to detect angular acceleration in three planes. Each canal has an ampulla containing the crista ampullaris.

Hearing loss caused by cochlear or retrocochlear pathology, producing equal reductions in air-conduction and bone-conduction thresholds (no air-bone gap). Patterns include low-frequency rising (Ménière's), asymmetric high-frequency downsloping (schwannoma), or symmetric high-frequency (presbycusis).

Vertical misalignment of the eyes producing vertical refixation on alternate cover testing. A central sign localising to the brainstem or cerebellum, and one of the three components of the HINTS examination. Skew in the context of acute vestibular syndrome strongly suggests stroke.

Group of autosomal-dominant hereditary cerebellar ataxias, over 40 subtypes described. SCA1, 2, 3 (Machado-Joseph), and 6 account for about 60% of dominant cases worldwide. Most are CAG-repeat expansion disorders; onset typically third to sixth decade. SCA2 is notable for saccadic slowing.

The vermal and paravermal cerebellar zones that receive spinal cord afferents and control trunk and limb coordination. Anterior-vermis lesions produce gait ataxia with relatively preserved limb function (the classical alcoholic-cerebellar-degeneration pattern); posterior-vermis lesions produce truncal ataxia with inability to sit unsupported.

Small horizontal saccades (0.5–5°) that move the eyes off fixation and bring them back after a brief intersaccadic interval of about 200 ms. A few per minute are normal; frequent (≥ 10/min) square-wave jerks indicate cerebellar pathology or, less commonly, progressive supranuclear palsy. Their pathological extension without intersaccadic interval is ocular flutter (and opsoclonus when multidirectional).

Actin-cored microvilli on the apical surface of hair cells, arranged in graded staircase rows. Mechanotransduction occurs when stereocilia are deflected toward the tallest row (the kinocilium in vestibular hair cells), tip-link tension opens cation channels, and the cell depolarises.

Superior division of the vestibular nerve, carrying afferents from the lateral and superior semicircular canals and the utricle. Most commonly affected division in vestibular neuritis. Function is tested with the head impulse, caloric, and oVEMP.

Any abnormal opening through the otic capsule that creates a low-impedance pathway for acoustic energy alongside the normal oval and round windows. SCDS is the prototype; other causes include large vestibular aqueduct, dehiscence of the posterior or lateral canal, and the X-linked DFN3 mixed hearing loss.

Vertigo or eye movement induced by loud sound — a feature of third-window disorders (SCDS), perilymph fistula, and rarely Ménière's. Reflects abnormal acoustic energy transfer into the labyrinth through a third window.

One of the two otolith organs in the vestibule, oriented approximately horizontally. Detects linear acceleration in the horizontal plane. Innervated by the superior vestibular nerve; utricular function is tested with the oVEMP.

Family of myogenic potentials evoked by acoustic or vibratory stimulation of the otolith organs. cVEMP (recorded from the sternocleidomastoid) tests the saccule and inferior vestibular nerve; oVEMP (recorded from inferior oblique) tests the utricle and superior vestibular nerve. Patterns of preservation and enhancement are diagnostic.

Intramural haemorrhage within the wall of the vertebral artery, often following minor trauma or neck strain. Leading cause of posterior circulation stroke in patients under 50. Neck pain or trauma preceding vertigo is the classic historical clue; urgent CTA or MRA of the vertebral arteries is the investigation of choice.

Recurrent vestibular symptoms in a patient with migraine. Episodes lasting 5 min–72 h with migrainous features (headache, photophobia, phonophobia, aura) in ≥50% — Bárány/IHS 2012 criteria. Propranolol and topiramate are first-line prophylactic agents.

Acute, persistent vestibular hypofunction from inflammation of the vestibular nerve. Continuous vertigo for days, peripheral HINTS pattern, no auditory symptoms. Bárány Society 2022 (Strupp et al.) renaming as acute unilateral vestibulopathy. Selective inferior-division involvement (5–15%) produces a distinctive pattern.

Benign nerve-sheath tumour of the vestibular nerve, usually arising at the cerebellopontine angle. Classically presents with asymmetric high-frequency SNHL, unilateral tinnitus, and gradual disequilibrium. AAO-HNS imaging threshold: 15 dB asymmetry at any single frequency on the audiogram.

Three-neuron reflex that stabilises the visual world during head movement by producing eye movements equal and opposite to the head movement. Latency ~7–10 ms. Tested at the bedside with the head impulse test and quantified in the lab with video-HIT or rotational chair testing.

The phylogenetically oldest cerebellar zone — the flocculus, nodulus, and parts of the uvula — that calibrates the vestibulo-ocular reflex and processes vestibular afferents. Lesions produce ocular abnormalities (downbeat nystagmus, gaze-evoked nystagmus, periodic alternating nystagmus, impaired smooth pursuit) without prominent limb ataxia.

Bilateral internuclear ophthalmoplegia with primary-position exotropia. Failure of adduction bilaterally on lateral gaze, with abducting nystagmus in the abducting eye. Preserved convergence. Almost pathognomonic for multiple sclerosis in a young patient.