What is the appropriate management for a patient presenting with a vestibular disturbance suspected to be related to a posterior fossa lesion, considering potential underlying conditions such as stroke or tumor?

Management of Vestibular Disturbance from Posterior Fossa Lesion

In patients with vestibular disturbance suspected to be related to a posterior fossa lesion, MRI brain without IV contrast is the recommended initial imaging modality, with urgent neuroimaging indicated when there are abnormal neurologic findings, abnormal HINTS examination by a trained specialist, or high vascular risk factors. 1

Initial Clinical Assessment

Categorize the Vestibular Syndrome

The first step is determining which vestibular syndrome pattern is present, as this drives the diagnostic and imaging approach 2:

• Acute vestibular syndrome: Continuous dizziness lasting days to weeks with nausea, vomiting, and head motion intolerance—includes vestibular neuritis, labyrinthitis, and posterior circulation stroke 2
• Triggered episodic syndrome: Brief episodes (<1 minute) with specific position changes—primarily BPPV 2
• Spontaneous episodic syndrome: Episodes lasting minutes to hours without triggers—includes vestibular migraine, Ménière's disease, vertebrobasilar TIA 2
• Chronic vestibular syndrome: Dizziness lasting weeks to months—includes posterior fossa masses 2

Critical Red Flags Requiring Urgent Neuroimaging

Any of the following mandate immediate MRI brain without IV contrast 1, 2:

• Abnormal neurologic examination findings (dysarthria, dysmetria, dysphagia, sensory/motor deficits, diplopia, Horner's syndrome) 2
• Severe postural instability with inability to walk safely 2, 3
• HINTS examination by trained specialist showing central features 1
• New-onset severe headache with vertigo 2
• Downbeating nystagmus on Dix-Hallpike without torsional component 2
• Direction-changing nystagmus without head position changes 2
• Pure vertical nystagmus without torsional component 2
• Nystagmus not suppressed by visual fixation 2

Imaging Strategy

Primary Recommendation

MRI head without IV contrast is the most sensitive test for posterior circulation infarcts and posterior fossa pathology 1. This is superior to CT, which misses a significant proportion of posterior fossa lesions 1.

When MRI is Not Immediately Available

• CT head without IV contrast may be appropriate as initial imaging before MRI, though it is less sensitive 1
• However, recognize that early MRI diffusion-weighted imaging can be falsely negative in 12% of cases when performed within 48 hours of symptom onset 4

Vascular Imaging Considerations

For chronic recurrent vertigo with brainstem neurologic deficits suggesting vertebrobasilar insufficiency 1:

• MRA head and neck or CTA head and neck are useful for evaluating the posterior circulation vasculature 1
• CTA has 100% sensitivity for vertebral artery dissection, compared to 77% for MRA 1
• The entirety of the vertebral artery from aortic arch to basilar artery should be evaluated 1

HINTS Examination (When Available)

The HINTS examination (Head Impulse, Nystagmus, Test of Skew) by a trained examiner has 100% sensitivity for posterior circulation stroke, superior to early MRI's 46% sensitivity 3, 4. This three-step bedside examination is more sensitive than early neuroimaging 4.

HINTS Findings Suggesting Central (Stroke) Pathology

• Normal horizontal head impulse test (normal vestibulo-ocular reflex) 4
• Direction-changing nystagmus in eccentric gaze 4
• Skew deviation (vertical ocular misalignment on alternate cover test) 4

The presence of any one of these findings is 100% sensitive and 96% specific for stroke 4. Skew deviation specifically predicts brainstem involvement and is present in 30% of cases with brainstem lesions 4.

High-Risk Patient Populations

Vascular Risk Factors Requiring Lower Threshold for Imaging

Even with normal neurologic examination, MRI may be helpful in patients with 1:

• Older age 1
• Hypertension 1
• Atrial fibrillation 1
• Nonwhirling type of dizziness 1
• Combined neurological symptoms 1

Approximately 25% of patients with acute vestibular syndrome have cerebrovascular disease, rising to 75% in high vascular risk cohorts 3. Critically, 75-80% of patients with posterior circulation infarct have no focal neurologic deficits on standard examination 3.

Specific Posterior Fossa Pathologies to Consider

Posterior Circulation Stroke

• Accounts for 3.6% of patients presenting with dizziness who have acute lesions 1
• Isolated transient vertigo may precede vertebrobasilar stroke by weeks or months 2
• Attacks typically last less than 30 minutes without hearing loss 2

Vestibular Schwannoma and Other Tumors

For chronic recurrent vertigo with unilateral hearing loss or tinnitus 1:

• MRI head and internal auditory canal (IAC) without and with IV contrast is useful for excluding vestibular schwannoma 1
• CT temporal bone without IV contrast can identify superior semicircular canal dehiscence 1
• 4% of patients with sudden sensorineural hearing loss have vestibular schwannoma 1

Cerebellar Pathology

For chronic disequilibrium with cerebellar ataxia signs 1:

• MRI head without IV contrast or MRI head without and with IV contrast assesses for cerebellar atrophy or other pathology 1
• MRI cervical and thoracic spine may be useful with additional spinal cord signs 1

Common Pitfalls to Avoid

• Do not rely on normal neurologic examination to exclude stroke—75-80% of posterior circulation strokes present without focal deficits 3
• Do not use CT as definitive imaging—it is insensitive for posterior fossa infarcts 1
• Do not delay imaging in high vascular risk patients even with peripheral-appearing symptoms 1
• Do not assume hearing recovery excludes tumor—recovery does not predict whether sudden hearing loss results from vestibular schwannoma 5
• Recognize that early MRI (<48 hours) can be falsely negative in 12% of acute strokes 4

When Imaging is NOT Indicated

• Brief episodic vertigo triggered by head movements with typical BPPV features on Dix-Hallpike (latency, fatigability, torsional nystagmus) 1
• Acute persistent vertigo with normal neurologic examination, normal HINTS by trained examiner, and low vascular risk 1
• Nonspecific dizziness without vertigo, ataxia, or neurologic deficits in low-risk patients 1