Background Lacunar infarcts are a type of ischemic stroke caused by the occlusion of small penetrating arteries that supply the subcortical deep brain structures such as the basal ganglia, thalamus, white matter of the internal capsule and pons. These arteries are susceptible to blockages due to conditions like hypertension and diabetes. Typical lacunar syndromes include pure motor hemiparesis, pure sensory, ataxic-hemiparesis, dysarthria-clumsy hand and sensory motor with minimal cortical findings. An atypical lacunar infarct can affect non-traditional brain regions and therefore present with unusual symptoms, challenging diagnosis and requiring careful consideration in clinical evaluation and management strategies.

Case Presentation A 75-year-old male with no significant past medical history presented to the ED with visual changes and dizziness that began a day prior. He reported lateral and downward deviation of the right eye and difficulty ambulating due to dizziness. In the ED, his blood pressure was 230/19 mmHg. Administration of amlodipine 5 mg was unsuccessful in reducing his blood pressure. A CT head with and without contrast, and a CTA of the head and neck, ruled out acute processes. Ophthalmology's differential included neurological causes involving the optic pathway to the lateral geniculate and conditions such as glaucoma. Neurology noted possible 3rd nerve involvement and ataxia, indicating the need to rule out a brainstem lesion. Significant adduction issues of the left eye and a positive Romberg’s sign were also observed. An MRI performed 3 days later revealed an acute lacunar infarct in the dorsal pons affecting the medial longitudinal fasciculus, alongside a mild burden of chronic small vessel ischemic changes in the periventricular and deep cerebral white matter and pons.

Discussion In the presented case, the patient's symptoms of visual changes, dizziness, and neurological deficits, initially perplexing with normal CT and CTA findings, ultimately led to the discovery of an atypical lacunar infarct in the dorsal pons. The involvement of the medial longitudinal fasciculus (MLF) explains the patient's distinctive clinical features, including lateral and downward deviation of the right eye, ataxia, and third nerve palsy. These findings underscore the variability in lacunar infarct presentations, necessitating a high index of suspicion and comprehensive evaluation, especially when initial imaging studies are inconclusive. Chronic small vessel ischemic changes observed on MRI highlight the cumulative vascular burden in the brain, suggesting a predisposing condition for the acute lacunar event. Management involves controlling vascular risk factors to prevent further infarcts and addressing specific neurological deficits through targeted therapies and rehabilitation. This case emphasizes the importance of detailed clinical assessment, multimodal imaging, and specialist consultation in unraveling atypical lacunar infarcts, ensuring appropriate diagnosis and management for optimal patient outcomes.