Temporal Evolution of Contrast Enhancement in Cranial Nerves: Insights from Heavily T2-Weighted 3D FLAIR Imaging

Abstract

Background: Cranial nerve enhancement is traditionally assessed with T1-weighted imaging, but heavily T2-weighted 3D FLAIR (HT2-FLAIR) imaging offers greater sensitivity to subtle T1 shortening. This study aimed to assess contrast enhancement of the oculomotor, trigeminal, and facial nerves using HT2-FLAIR imaging. Methods: This retrospective repeated-measures cohort study included 33 patients. We subjectively assessed contrast enhancement of the cisternal segments of these three cranial nerves across precontrast, postcontrast, and 4 h delayed postcontrast HT2-FLAIR images and objectively evaluated serial changes in the signal intensity ratio (SIR)—the ratio of each structure’s signal intensity to that of the pons—for the oculomotor and trigeminal nerves, cerebrospinal fluid (CSF) spaces, and choroid plexus. Results: Subjectively, a high rate of enhancement (>90%) was observed bilaterally for all three nerves on 4 h delayed postcontrast images. Objectively, SIR of both the oculomotor and trigeminal nerves peaked on 4 h delayed postcontrast images, followed by postcontrast images, paralleling the pattern of CSF spaces and differing from that of choroid plexus. Conclusions: This study is the first to show that HT2-FLAIR imaging can visualize temporal enhancement of the cisternal segments of cranial nerves. Extravascular gadolinium may represent an alternative mechanism for normal cranial nerve enhancement.