The hints for posterior circulation stroke are identified through specific findings in the Head Impulse–Nystagmus–Test of Skew (HINTS) examination, which helps differentiate central causes (like stroke) from peripheral vestibular issues in patients experiencing acute vestibular syndrome.
The HINTS test comprises three key assessments:
1. Head Impulse Test (HI)
This test assesses the vestibulo-ocular reflex (VOR).
- Hint for Stroke: A normal horizontal head impulse test suggests a central cause. In this finding, when the examiner rapidly turns the patient's head to one side while the patient keeps their eyes fixed on the examiner's nose, the patient's eyes remain fixed on the target without a corrective refixation saccade. This "normal" VOR in the presence of acute vertigo points towards a brainstem or cerebellar lesion (stroke).
- Contrast (Peripheral Vertigo): An abnormal head impulse test (where the eyes are dragged off target and then make a quick corrective movement back to the target) typically indicates a peripheral vestibular problem (e.g., labyrinthitis, vestibular neuritis).
2. Nystagmus (N)
This part examines involuntary rhythmic eye movements.
- Hint for Stroke: Gaze-direction nystagmus (also known as gaze-evoked nystagmus) suggests a central cause. This type of nystagmus changes direction depending on the direction of gaze (e.g., beats to the right when looking right, and to the left when looking left). Vertical nystagmus (beating purely up or down) is also a strong indicator of a central lesion.
- Contrast (Peripheral Vertigo): Unidirectional nystagmus that does not change direction with gaze and is often suppressed by visual fixation is characteristic of a peripheral vestibular problem.
3. Test of Skew (TS)
This test checks for vertical misalignment of the eyes.
- Hint for Stroke: The presence of eye skew deviation suggests a central cause. This is observed as a vertical misalignment of the eyes, where one eye moves down and then up to refixate when covered and uncovered (cover-uncover test), indicating a lesion in the brainstem or cerebellum affecting vertical gaze pathways.
- Contrast (Peripheral Vertigo): The absence of skew deviation is typical in peripheral vestibular disorders.
Summary of HINTS Findings for Posterior Circulation Stroke
A positive HINTS test, indicating a higher likelihood of posterior circulation stroke in acute vestibular syndrome, is present when any of the following three signs are observed:
| HINTS Component | Finding Suggesting Posterior Circulation Stroke (Central) | Finding Suggesting Peripheral Vertigo |
|---|---|---|
| Head Impulse | Normal (eyes stay on target, no corrective saccade) | Abnormal (corrective saccade present) |
| Nystagmus | Gaze-direction (changes direction with gaze), Vertical | Unidirectional, fixed, suppressed by fixation |
| Test of Skew | Present (vertical eye misalignment) | Absent |
Practical Considerations:
The HINTS examination is a bedside tool for clinicians evaluating patients with acute onset of persistent dizziness or vertigo, especially when accompanied by other neurological symptoms, to quickly assess the risk of stroke. It is particularly valuable in the emergency setting to guide further diagnostic imaging and management.
