Spectrum and Mimics of Brain Surface Enhancement on Postcontrast FLAIR Images

Brain surface enhancement on FLAIR describes increased FLAIR signal at the brain surface after the administration of gadolinium-based contrast agents. Because of the unique properties of the FLAIR sequence, pathology at the brain surface may be obvious on postcontrast FLAIR but inconspicuous on postcontrast T1 imaging. Following administration of gadolinium-based contrast agents, brain surface enhancement on FLAIR can be seen as leptomeningeal enhancement on FLAIR and/or CSF enhancement on FLAIR. Leptomeningeal enhancement on FLAIR manifests due to a combination of cortical and leptomeningeal inflammation as well as vascular congestion or engorgement. CSF enhancement on FLAIR manifests as elevated subarachnoid FLAIR signal due to leakage of small quantities of gadolinium-based contrast agent into the CSF from breakdown of the BBB and/or blood-CSF barrier and is sometimes associated with leptomeningeal enhancement on FLAIR. CSF enhancement on FLAIR has been previously described as a hyperintense acute reperfusion marker in the setting of stroke, TIA, and endovascular therapies. This article reviews brain surface enhancement on FLAIR, with leptomeningeal enhancement on FLAIR and CSF enhancement on FLAIR, presented in the setting of stroke, meningitis, encephalitis, posterior reversible encephalopathy syndrome, seizures, trauma, demyelinating disease, malignancy, diseases of vascular engorgement such as Moyamoya and Sturge-Weber syndrome, and chronic age-related microvascular disease. The utility of brain surface enhancement on FLAIR as a biomarker of BBB/blood-CSF barrier dysfunction is also discussed.Learning Objective: To recognize brain surface enhancement on FLAIR imaging as leptomeningeal enhancement on FLAIR and CSF enhancement on FLAIR in normal aging and a wide variety of intracranial diseases; to understand that FLAIR imaging is more sensitive than T1-weighted imaging for pathology at the brain surface; and to understand the potential of brain surface enhancement on FLAIR as a biomarker of BBB or blood-CSF barrier dysfunction