MRI Yield of Posterior Fossa Strokes in ‘Dizzy’ Patients

Abstract

pre-syncope and unsteadiness [1]. The posterior circulation is defined primarily by the vertebro-basilar arterial system, which arises from the subclavian arteries. Infarcts affecting the superior or Posterior Inferior Cerebellar Arteries (PICA) can cause symptoms of vertigo.Many patients with unexplained dizziness ultimately undergo an MRI scan to rule out a posterior circulation ischaemic stroke. Prior research showed that only 3.2% of patients presenting with dizziness, vertigo or imbalance were diagnosed with a stroke or Transient Ischaemic Attack (TIA) [2]. Vestibular symptoms such as vertigo can be attributed to both peripheral causes such as vestibular neuritis or central causes like brainstem/cerebellar stroke. In a study of 240 patients who presented with vertigo lasting more than a day and no other focal neurological deficits, 10% were diagnosed with cerebellar strokes but ischaemia associated with vertigo is often accompanied by other brainstem signs [3]. However, only 17% of patients with confirmed PICA strokes had symptoms of vestibular neuritis [3]. Manoeuvres such as Dix-Hallpike can help distinguish between peripheral or central aetiology since none of the patients who had symptoms of vestibular neuritis due to ischaemic stroke had a positive head thrust [4]. Nevertheless, it has been argued that MRI plays an important role in differentiating between peripheral and central aetiology when clinical diagnosis fails [5].CT scan has been proven to have poor sensitivity in diagnosing posterior Fossa strokes in patients with dizziness and vertigo as it provides suboptimal visualisation of structures secondary to artefact produced by bony structures of the cranial base and therefore early ischaemic events are missed [5,6]. Accordingly, diffusion weighted MRI scans is more commonly used, but even this modality misses up to 20% posterior Fossa infarcts in the first 24-48 hours of presentation [1]. The yield of MRI for stroke in this cohort of patients was only 21%, with a diagnostic impact on management for 22% of these patients [5]. This unreliability of MRI scan is reinforced by a study which showed that diffusion weighted imaging was falsely negative in 12 of patients with acute vestibular symptoms and posterior Fossa strokes [7]. MethodA total of 603 MRI scans were performed for patients presenting with vertigo and dizziness with suspicion of cerebellar or brainstem infarcts during the one year period analysed at Royal Derby Hospital. Prior research showed that there is a low yield of posterior circulation infarcts diagnosed on MRI in this cohort of patients with dizziness [1,5].Data was accumulated for those 603 patients with MRI scans through screening of patients who underwent MRI scan in the last year and key words on the request or report cards included 'cerebellar infarct' , 'cerebellar stroke' , 'brainstem stroke' , 'vertigo' , 'dizziness' , 'ataxia' or 'unsteadiness' . Methods: 588 patients under went MRI within a one-year period. Data was ascertained through requests and results on ICM compute...