Figure 1.

(a) Axial sections of T2-weighted images obtained 20 hours after the onset of symptoms showed areas of increased signal intensity in the left mesencephalon and (b) paramedian thalamic nuclei. (c, d) Axial brain FLAIR images. Hyperintense signals in the rostral midbrain and the paramedian thalamic suggest acute Percheron artery infarction. (c) “V-shaped” hyperintense signal along the pial surface of interpeduncular fossa in midbrain. The mesencephalon lesion extends to the periaqueductal gray matter. (e) MR angiography shows a right-sided FPCA (thick white arrow), arising directly from the ipsilateral internal carotid artery. Patency of the basilar artery and tip, left PCA, and posterior communicating artery; the thin arrows indicate the superior cerebellar arteries, with normal appearance. (f) Sagittal section, T1-weighted: showed ill-defined areas of hypodensity in the thalamopeduncular junction (white arrows). (g) Sagittal section, FLAIR: hyperintense images with the same topography. Coronal sections on T2 (h) and FLAIR images (i, j). Relatively symmetric hyperintense signals in the paramedian inferior thalami, extending (asymmetrically) into the medial and rostral mesencephalon (territory of the artery of Percheron). (i) Coronal section, FLAIR: “lambda-shaped” (Λ) hyperintense signal, adjacent to the pial layer of the interpeduncular fossa, next to the infarction zones in the thalamic–mesencephalon junction, equivalent version of the “V-shape” observed in axial sections (c). (FLAIR, fluid-attenuation inversion recovery images; FPCA, fetal posterior cerebral artery.)