Teaching Case

A 48-year-old male presented to the emergency department with sudden onset dizziness and internuclear ophthalmoplegia. He has a history of an astrocytoma removal at the age of 12 with no residual neurological deficits present following the surgery, and he has no other medical history or regular medications.

Computed Tomography (CT) angiogram, venogram and non-contrast studies were performed and did not display any evidence of established infarct or other intracranial pathology. On MRI, a small focus of restricted diffusion with minor high signal on FLAIR sequences in the right parasagittal dorsal pons was seen (Figure 1a). Taking into account the patient’s clinical condition and the anatomic location of the lesion, these findings were consistent with acute ischaemia involving the medial longitudinal fasciculus (MLF). The patient did not have pericallosal/callosal/periventricular or juxta-articular lesions in the supratentorial parenchyma.

Background

Internuclear ophthalmoplegia (ION) is a pathognomic clinical sign of a lesion in the medial longitudinal fasciculus (MLF), a myelinated nerve bundle travelling through the midbrain and dorsal pons that is essential for extraocular muscle movement. As a result, lesions within the MLF can alter the ability to maintain a fixed gaze during head movement, affecting balance and gait [1]. The two most common aetiologies for MLF lesions are cerebrovascular accidents (CVA) and multiple sclerosis (MS).

Clinical Perspective

Dizziness is the primary reason for 2–4% of emergency presentations and is a secondary symptom in up to 10% of emergency presentations [2], with 78% of patients with MLF lesions having dizziness as a shared symptom between them [1]. With more than 95% of dizziness presentations not having ischaemic aetiology, the low sensitivity of CT scans in acute ischaemia, and the impracticality of MRI in the ED setting, history and examination remains the most effective assessment [3]. One retrospective study of patients presenting to the ED with dizziness and cardiovascular risk factors found that the presence of a focal neurological finding had the highest association with ischaemia [4]. Ammar et al. have also shown that gait abnormalities and focal neurological deficits were the most significant predictors of a central aetiology in patients presenting with dizziness [5].

Imaging Perspective

The CT scan requested from the Emergency Department showed no significant alterations. Given the ongoing ophthalmoplegia, the patient was admitted for an inpatient MRI scan, which was performed the next day, showing restricted diffusion in the tegmentum of the midbrain involving the MLF, as evidenced by a minor high signal of the FLAIR series and a low signal in the ADC series. The patient did not have pericallosal/callosal/periventricular or juxta-articular lesions in the supratentorial neuroparenchyma to suggest the presence of multiple sclerosis.

Outcome

Multiple sclerosis and vasculitis screening were negative, and the patient was discharged with dual antiplatelet therapy. Cardiovascular analysis was completed as an outpatient and there were no significant findings. The presented case is not only an example of a pathognomic finding of a rare lesion, but it also highlights that even without obvious risk factors, isolated dizziness is a symptom that warrants thoughtful history and clinical examination.

Written informed patient consent for publication has been obtained.