When sulcal enhancement is not leptomeningeal metastasis: diagnostic value of T1-T2FLAIR matching for differentiating benign contrast leakage.

The incidence and imaging characteristics of non-neoplastic sulcal enhancement on contrast-enhanced T2-weighted fluid-attenuated inversion recovery (CE-T2FLAIR) imaging in routine neuro-oncologic magnetic resonance imaging (MRI) were investigated. Contrast-enhanced T1-T2FLAIR sequence matching was used to differentiate benign contrast leakage from leptomeningeal metastasis (LMS). This retrospective, single-center study included 337 patients who underwent contrast-enhanced brain MRI for evaluation of suspected intracranial metastasis. Sulcal enhancement on CE-T2FLAIR was classified as absent, contrast leakage, or LMS based on imaging and clinical criteria. Two neuroradiologists independently determined T1-T2FLAIR matching status. Overall, 271 showed no leptomeningeal enhancement; 55 patients demonstrated contrast leakage and were older than the other groups; 11 were accurately diagnosed with LMS. Using match positivity as the cutoff, sensitivity and specificity were 90.9% and 94.8%, respectively for the LMS diagnosis. Mismatch patterns were common in contrast leakage and associated with older age, higher cerebral microbleed burden, cortical superficial siderosis, and prior radiotherapy. Non-neoplastic sulcal enhancement on CE-T2FLAIR is a common finding in contemporary neuro-oncologic MRI, particularly with delayed post-contrast acquisition. Assessing agreement between CE-T2FLAIR and contrast-enhanced T1-weighted imaging provides a simple and robust method for distinguishing benign contrast leakage from LMS.