Address for correspondence : Chang Eun Song, MD, Department of Otorhinolaryngology, Myongji Hospital, 55 Hwasu-ro 14beon-gil, Deogyang-gu, Goyang 412-270, Korea
Tel : +82-31-810-5445, Fax : +82-31-810-6357, E-mail : entsong@gmail.com

Introduction

Acute vestibular neuritis (VN) without neurological symptoms or signs is one of the most common acute peripheral vestibulopathies (APV), which is characterized by acute onset of long-lasting (several days) vertigo, spontaneous unilateral horizontal and torsional nystagmus toward the contralesional side, and ipsilesional canal paresis to caloric stimulation.¹⁾ However, central pathologic conditions may also present with symptoms or signs that mimic vestibular neuritis, which have been called pseudo-VN.²⁾
Although an extensive retrospective cohort study has reported that less than 1% of patients with acute isolated vertigo have a central pathology, delayed or missed diagnosis of infarction may result in critical morbidity and mortality.³⁾ Therefore, some authors suggested that among the cerebellar infarction patients with fixed and persistent spontaneous nystagmus, 1) older patients, 2) any patient with vascular risk factors showing negative head thrust test, and 3) patients showing direction-changing gaze-evoked nystagmus or severe ataxia can be suspected for pseudo-VN and hence require brain magnetic resonance image (MRI).²⁾
Here we report a case of a young patient free of vascular risk factors, who developed cerebellar infarction with contralesional canal paresis possibly due to an embolism from bilateral vertebral artery dissection (VAD).

Case

A 39-year-old female patient without any stroke risk factors was hospitalized after an acute onset of severe vertigo, nausea, and vomiting. The patient only complained of vomiting and dizziness without any complaint of headache, neck pain, or hearing impairment. The patient had no previous known stroke risk factors such as hypertension, diabetes mellitus, smoking history or prior stroke. Examination of the cranial nerve function including pupillary reflex revealed normal. The motor and sense of the extremities were normal. Due to severe dizziness and fatigue, righting reflex could not be tested but cerebellar function test did not reveal any typical abnormal findings such as dysmetria. Videonystagmography (VNG) showed left-beating horizontal nystagmus with torsional component compliant with the Alexander's law. After head shaking, the degree of left-beating nystagmus was augmented. Head thrust test (HTT) revealed a corrective saccade typically seen in acute VN. Subjective visual vertical (SVV) test with binocular viewing showed 6.0 degree tilt toward the right side (normal range in our institute: -2.0 to 2.3 degree). The patient strongly refused hospitalization because she thought that she would not be able to breastfeed her newborn baby in the proper atmosphere. When the VNG test was repeated before discharge from the emergency unit, a direction-changing gaze evoked nystagmus (GEN) was recorded. In order to rule out any central pathology, a diffusion brain MRI was performed. MRI demonstrated acute cerebellar infarction that involved the territory of the medial branch of posterior inferior cerebellar artery (mPICA) and superior cerebellar artery (SCA) on the left side (Fig. 1). The patient was then admitted to the department of neurology after which anticoagulant therapy was instituted.
On the first day of admission, neck MRA showed wide range of diffuse severe stenosis of the right vertebral artery (VA) sparing only the V4 segment. Left VA revealed narrowing of the V2 segment and dissecting aneurysm (Fig. 2). On the fourth day of admission, transfemoral cerebral angiography was performed, which demonstrated complete reperfusion of both VAs together with wide range of luminal irregularity of both VAs and dissecting aneurysm of the left VA (Fig. 3). Vertigo disappeared completely by the third day of hospitalization, and abnormal nystagmus was absent on follow-up VNG testing except for a positive HTT. SVV tilt of the patient was normalized (0.1° tilt toward right side). Refixation saccade during HTT disappeared on the fourth day of hospitalization. On the vestibular function tests performed four days after hospitalization, bithermal caloric test revealed a 68.3% decrease in caloric response on the right side, while vestibular evoked myogenic potential test was normal. The result of pure-tone audiogram was unremarkable. On day 5, the patient was discharged relieved of all symptoms.

Discussion

Approximately 11% of patients with isolated cerebellar infarction have shown vertigo as an isolated symptom, and most (96%) of them had infarction in the territory of mPICA.²⁾ The nodulus, which is supplied by mPICA, is a critical structure in determining the direction specific pattern of otolith dysfunction and in eliciting cerebello-vestibular connections by the inhibitory nodulovestibular Purkinje fibers in PICA territory cerebellar infarction.^2,4) When it is involved pathologically, the patient presents with contraversive tilts of SVV, ocular torsion, and skew deviation as well as spontaneous unidirectional nystagmus; therefore, patients with mPICA territory cerebellar infarction may sometimes be misdiagnosed with acute VN.^2,4) On the other hand, since the superior cerebellum supplied by the SCA does not have significant vestibular connections, cerebellar infarction in the SCA rarely causes vertigo. Prominent body lateropulsion in isolated medial SCA territory cerebellar infarction may be explained by involvement of rostral vermis that is related predominantly to gait, muscle tone, and postural control.⁵⁾
The exact pathomechanism of VAD is unknown. The hemorrhage that occurs in arterial dissection usually involves an intimal tear or bleeding of the vasa vasorum that gives rise to blood extending into the medial layer. This can eventually lead to narrowing of the vessel lumen with resultant partial or complete obstruction. Thrombotic or embolic complications may follow.⁶⁾ Some authors have suggested that an artery-to-artery embolism may result in labyrinthine artery infarction giving rise to vertigo and hearing loss.⁷⁾ The embolism in vertebrobasilar system may cause various symptoms, such as isolated vertigo, isolated deafness, or vertigo and deafness, depending on the branches involved.⁷⁾
Our case demonstrated cerebellar infarction involving multiple vascular territories including mPICA and SCA on the left side caused by spontaneous bilateral VAD that presented with unusual findings such as a contralateral canal paresis and contraversive SVV tilt, and a positive HTT lasting for 3 hospital days. Although our patient's VNG results were compatible with the previously explained pathomechanism of pseudo-VN, the findings such as canal paresis and positive HTT of our patient are far from the typical findings of left cerebellar infarction. When the unilateral cerebellum (including nodulus) is damaged, SVV angle tilts to the contralesional side. There-fore, the authors speculate that the hypoperfusion of the contralesional anterior vestibular artery, which supplies the utricle, superior part of saccule and ampulae of the anterior and horizontal semicircular canals, may have resulted in vestibular ischemia causing the contralesional canal paresis and contraversive tilt of SVV as well as positive finding of HTT since the lesion did not involve the nodulus or the uvula in the present case.
Central pathology cannot be ruled out merely with an isolated sign or through simple physical examination in the diagnosis of APV. Nevertheless, HTT is the single most valuable diagnostic test in distinguish APV from stroke in patients with isolated vertigo. A recent study reported that three oculomotor assessments (including HTT, redirective GEN by eccentric gaze, and skew deviation) can potentially achieve 100% sensitivity and 96% specificity in differentiating acute dizziness caused by an infarction.⁸⁾
Because our patient showed typical nystagmus of APV (unidirectional spontaneous nystagmus consistent with the Alexander's law and a positive HTT) in the initial physical examination, a central pathology was masked in differentiating from APV. If the redirective GEN had not been observed on the follow-up VNG test, the patient might have suffered catastrophic complications. Indeed, HTT and GEN do require skillfulness and experience for proper interpretation and the results are potentially subject to examiner bias.
In this case, a young patient who developed pseudo-VN was comorbid with vestibular infarction from spontaneous bilateral VAD. This suggests that the contralesional vascular ischemia from bilateral VAD may cause vestibule-ocular reflex impairment masking a central pathology. We suggest that physicians should pay careful attention to other subtle findings, such as GEN or skew deviation, even if HTT shows positive result in patients with isolated vertigo.

1. Strupp M, Brandt T. Vestibular neuritis. Adv Otorhinolaryngol 1999;55:111-36.

2. Lee H, Sohn SI, Cho YW, Lee SR, Ahn BH, Park BR, et al. Cerebellar infarction presenting isolated vertigo: frequency and vascular topographical patterns. Neurology 2006;67(7):1178-83.

3. Kerber KA, Brown DL, Lisabeth LD, Smith MA, Morgenstern LB. Stroke among patients with dizziness, vertigo, and imbalance in the emergency department: a population-based study. Stroke 2006;37(10):2484-7.

4. Kim HA, Lee H, Yi HA, Lee SR, Lee SY, Baloh RW. Pattern of otolith dysfunction in posterior inferior cerebellar artery territory cerebellar infarction. J Neurol Sci 2009;280(1-2):65-70.

5. Nitschke MF, Kleinschmidt A, Wessel K, Frahm J. Somatotopic motor representation in the human anterior cerebellum. A high-resolution functional MRI study. Brain 1996;119(Pt 3):1023-9.

6. Choi KD, Chun JU, Han MG, Park SH, Kim JS. Embolic internal auditory artery infarction from vertebral artery dissection. J Neurol Sci 2006;246(1-2):169-72.

7. Kim SH, Kosnik E, Madden C, Rusin J, Wack D, Bartkowski H. Cerebellar infarction from a traumatic vertebral artery dissection in a child. Pediatr Neurosurg 1997;27(2):71-7.

8. Kattah JC, Talkad AV, Wang DZ, Hsieh YH, Newman-Toker DE. HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke 2009;40(11):3504-10.