A 90-year-old female with hypertension was admitted to the emergency room with acute-onset dysarthria and dizziness persisting for 6 hours without any other neurological deficits. Initial diffusion-weighted imaging (DWI) revealed subtle diffusion-restricted lesions in the bilateral anteromedial portions of the midbrain tegmentum (Fig. 1-A, B). Computed tomography perfusion revealed cerebral hypoperfusion extending ventral to the aqueduct in the bilateral paramedian part of the midbrain (Fig. 1-C). CTA revealed a fetal variant of the right posterior cerebral artery (PCA) without significant stenosis in other intracranial arteries (Fig. 1-D, E). Informed consent was obtained from the patient for publishing this case report, and the local Institutional Review Board (IRB) approved its design (IRB No. 2024GR0042).

Two days after admission, the patient’s neurological status deteriorated, as evidenced by more-prominent bilateral paramedian lesions in follow-up DWI (Fig. 1-F). This deterioration was associated with clinical symptoms of wall-eyed bilateral internuclear ophthalmoplegia and ataxia affecting both upper and lower extremities (Fig. 1-G). TFCA was used to further assess the lesion attributes and hidden vascular pathologies. A deep perforator of the distal BA was identified in a conventional angiography image (Fig. 2-A). Multiplanar reformatting imaging revealed a single common perforator entering the interpeduncular fossa, which appeared to be associated with the ischemic lesion (Fig. 2-B). VWI performed to obtain additional information about the vascular abnormalities confirmed the detailed trajectory of the perforator from the distal BA directly toward the ischemic lesion (Fig. 2-C, D) and revealed abnormal vessel-wall enhancement of this perforator (Fig. 2-E, F).

Serum laboratory findings were normal, including the levels of vitamins B1 and B12, blood urea nitrogen, ammonia, glucose, and electrolytes, which ruled out any other causes of the bilateral midbrain lesions. Furthermore, no other potential sources of stroke were found, leading to the final diagnosis of bilateral pure midbrain infarction resulting from an abnormality in the single perforator of the distal BA. The neurological state of the patient gradually improved over 2 weeks, and she was discharged in a stable condition.

This was a rare case of bilateral pure midbrain infarction caused by an abnormality in the single common perforator of the distal BA supplying both sides of the paramedian part of the midbrain. Bilateral midbrain infarction can result from severe stenosis or occlusion of the BA and VAs, but the occurrence of pure midbrain infarction without the involvement of other structures such as the thalamus or pontine is uncommon [3,4]. The blood supply to the paramedian and central parts of the midbrain is typically associated with perforators from the PCA, such as the thalamoperforating, peduncular, and mesencephalic arteries [5]. The well-known rostral group of perforators from the distal BA typically extend into the interpeduncular fossa, but their direct involvement in supplying the paramedian part of the midbrain, as seen in the present case, has been rarely documented [5,6]. Therefore, pure bilateral midbrain infarction caused by a single deep perforator abnormality without significant large-vessel involvement can be difficult to diagnose. TFCA and high-resolution VWI offered important insights into the underlying pathology of the stroke in the present case.

Diagnostic cerebral angiography is well known for providing detailed information about intracranial arteries, and VWI is widely recognized for its accurate assessments of the wall pathology and pathways of large arteries [7]. The present case demonstrates how the combined use of diagnostic cerebral angiography and high-resolution VWI also enables 1) the identification of specific deep perforators contributing to the lesion from among numerous deep perforators, 2) the precise mapping of their trajectories to visualize the correlation with the affected parenchymal lesions, and 3) the detection of their abnormal vessel-wall enhancement. This case thus provides additional diagnostic insights for determining the etiology of stroke caused by unusual deep perforator problems, which may not be fully explained by simple conventional techniques.