Siltation and tidal effects: a comprehensive, clinical, and didactic approach to reasoning about vertebrobasilar hypoflow conditions

OBJECTIVES: To propose a clinically applicable model for understanding vertebrobasilar hypoperfusion by categorizing its causes into two mechanisms: the siltation effect, related to local vascular obstruction, and the tidal effect, related to systemic reduction in posterior circulation blood flow. METHODS: A non-systematic narrative review was conducted using selected literature in the fields of neurotology, vascular neurology, and cardiovascular medicine. The analogy of coastal rivers affected by sedimentation and tides was used to explain the proposed classification. Clinical examples were drawn from studies on vertebral artery narrowing, subclavian steal syndrome, dolichoectasia, small vessel pathology, orthostatic hypotension, cardiac disorders, anemia, and abnormal blood pressure regulation. RESULTS: The siltation effect includes conditions that block or reduce blood flow within the vertebrobasilar system, such as atherosclerosis, vessel compression, and dissection. The tidal effect includes disorders that globally impair perfusion, such as heart failure, low blood pressure, reduced oxygen delivery, and circadian blood pressure extremes. Combined situations, such as arterial hypotension, vessel stenosis, sleep disorders and migraine are common and may increase the risk of transient ischemic events or stroke. CONCLUSION: The distinction between siltation and tidal effects provides a useful clinical reasoning model for diagnosing and managing patients with symptoms suggestive of vertebrobasilar hypoflow, including vertigo, dizziness, and transient brainstem symptoms. Recognizing the frequent coexistence of these mechanisms reinforces the need for a comprehensive, multidisciplinary approach to ensure accurate diagnosis and guide appropriate therapeutic decision-making.