Many patients presenting to the emergency department with dizziness report an acute onset of persistent vertigo. These individuals often exhibit spontaneous nystagmus, consistent with Alexander’s law, and show a positive head impulse test result during neurological examination. These findings suggest acute unilateral vestibulopathy, a form of peripheral vertigo. However, distinguishing this form from other causes of central vertigo can be challenging. One such condition is labyrinthine infarction, which is difficult to detect using standard imaging techniques. Herein, we report a rare case of labyrinthine infarction, with a thrombus identified on early susceptibility-weighted imaging (SWI).
CASE
A 72-year-old woman with no significant medical history presented to the emergency department with a 2-day history of vertigo. She reported acute onset of persistent spontaneous vertigo accompanied by nausea and vomiting. Initial neurological examination revealed left-beating spontaneous nystagmus consistent with Alexander’s law and a positive head impulse test with right catch-up saccades. Additionally, skew deviation was not observed. Cerebellar examination did not show lateralization, and there were no other focal neurological deficits. Laboratory tests, including complete blood count with differential, serum electrolytes, glucose, liver function tests, blood urea nitrogen, and creatinine levels, were all within normal limits.
Further evaluation with computed tomography (CT) and magnetic resonance imaging (MRI) was performed. CT angiography revealed no parenchymal hemorrhage or patent flow in the vertebrobasilar artery and both anterior inferior cerebellar arteries (AICA) (Fig. 1A, 1B). MRI identified only mild small-vessel ischemic lesions in both the centrum semiovale and subcortical white matter, with no evidence of acute hemorrhage or infarction (Fig. 1C). The patient was initially suspected to have unilateral vestibulopathy, such as vestibular neuritis, and was discharged from the emergency department with medications for symptom control.
Six days later, the patient returned to the emergency department with worsening symptoms, including persistent vertigo, dysarthria, and hearing impairment in the right ear. Neurological examination revealed mild dysarthria, ongoing left-beating spontaneous nystagmus with right catch-up saccades on the head impulse test, and mild ataxia and dysdiadochokinesia in the right upper limb. The Dix-Hallpike test, head roll test, and head shaking test yielded normal findings. After suspecting central vertigo, follow-up imaging with CT angiography and MRI were performed.
CT angiography revealed a steno-occlusion of the right AICA, which appeared normal at the initial visit (Fig. 2A, 2B). MRI demonstrated diffusion restriction in the right cerebellar peduncle, indicating an acute infarction in the AICA territory (Fig. 2C). SWI also revealed a dark signal in the right AICA. At this point, the patient was diagnosed with cerebellar peduncle infarction caused by a right AICA thrombus. Subsequently, a thorough retrograde review of the MRI scan from the initial visit revealed a small dark signal in the right labyrinthine artery on SWI (Fig. 1D). This finding led to a retrospective diagnosis of labyrinthine artery infarction at the initial visit.
The patient was diagnosed with acute right AICA infarction and was started on aspirin and clopidogrel. Further evaluation, including a stroke etiology study, conservative care, and rehabilitation, was performed during admission. The etiological study, which included blood tests, echocardiography, Holter monitoring, and patent foramen ovale evaluation, revealed no significant abnormalities, leading to a classification of undetermined etiology. As symptoms improved over the following days, the patient was discharged on antiplatelet therapy.
DISCUSSION
Despite thorough neurological examination, differentiating acute labyrinthine artery infarction from peripheral vertigo remains challenging. The current imaging techniques often fail to detect isolated labyrinthine artery infarctions, making the diagnosis via imaging studies difficult.1 Differentiation of labyrinthine infarction from vestibular neuritis should initially rely on detailed history taking along with physical and neurologic examinations.2 However, in cases of isolated labyrinthine infarction without concurrent AICA territory or brainstem infarction, neurologic examination findings can be indistinguishable from those of vestibular neuritis. Both conditions present with spontaneous nystagmus away from the lesion and positive head impulse test results.3 While the HINTS-plus can aid in differentiating conditions by detecting hearing loss, it may still be insufficient, as auditory symptoms can be subtle or transient, making it challenging to distinguish conditions solely through neurologic examination.2 Additionally, differentiation is often difficult because lesions frequently remain undetected on standard diffusion MRI. The presence of associated infarctions in the flocculus or other AICA territory areas can aid in differentiation; however, these may also go undetected.4 As a result, many cases of initially isolated labyrinthine infarction may be missed and only detected later, as neurologic symptoms progress, and AICA infarction becomes evident.5 Few cases of isolated labyrinthine infarction with MRI findings have been described in the existing reports.6 Here, we present a case initially diagnosed with clinical vestibular neuritis, which revealed a thrombus in the labyrinthine artery on SWI, indicating labyrinthine artery infarction. We suggest that a thoroughly evaluated SWI can help differentiate labyrinthine artery infarction from other types of peripheral vertigo.