Leptomeningeal Enhancement at 7T in Multiple Sclerosis: Frequency, Morphology, and Relationship to Cortical Volume

Abstract

Background and purpose: Perform an investigation of the frequency and distribution of leptomeningeal enhancement on postgadolinium magnetization-prepared FLAIR (MPFLAIR) in multiple sclerosis (MS) on 7 Tesla (7T) MRI and to relate this finding to measures of brain structure and lesion volumes.

Methods: Twenty-nine participants with MS underwent 7T MRI of the brain. Three healthy volunteers (HVs) were scanned for comparison. Areas of postcontrast leptomeningeal enhancement were identified. Images were segmented for brain structure and lesion volumes. The relationship between leptomeningeal enhancement and clinical and volumetric data was explored.

Results: Two patterns of enhancement were found: "nodular" (discrete, spherical nodules at the pial surface or subarachnoid space) and "spread/fill" (appearance of contrast spread through the local subarachnoid space). Twenty-six of 29 (90%) MS participants had at least one focus of leptomeningeal enhancement. Nodular foci were present in 15 of 29 (51%) MS participants. Spread/fill foci were present in 22 of 29 (76%) MS participants. Two HVs had examples of nodular foci, but none had spread/fill enhancement. MS participants with spread/fill foci were older (48.9 years [SD 8.3]) than those without (33.3 years [SD 11.5], P = .005). MS participants with spread/fill foci had reduced cortical gray matter volume compared to those without (P = .020).

Conclusions: Leptomeningeal enhancement on postcontrast 7T MPFLAIR is more prevalent than prior reports at 3T-occurring at frequencies closer to histopathologic data. Spread/fill foci are associated with reduced cortical gray matter volumes and may represent blood-meningeal barrier breakdown near sites of meningeal inflammation, whereas nodular foci may be a normal variant.

Keywords: 7 Tesla; Multiple sclerosis; meningeal; meningeal enhancement; meningeal inflammation; ultra-high field MRI.

Figure 1. Method for identification of leptomeningeal enhancement

Images from a 38-year-old woman with secondary progressive multiple sclerosis treated with dimethyl fumarate. Shown are magnetization prepared fluid attenuated inversion recovery (MPFLAIR) pre-contrast (A) and post-contrast (B) images. The pre-contrast image was digitally subtracted from the pre-contrast image to create the subtraction image (C). Areas of hyperintensity on the subtraction image were thus present on post-contrast images and not on the pre-contrast image. An example is highlighted by the red circle.

Figure 2. Examples of “nodular” type enhancing foci in multiple sclerosis

Images from a 49-year-old man with relapsing-remitting multiple sclerosis (RRMS) treated with fingolimod (A–D) and a 51 year old man (E–H), both with RRMS treated with dimethyl fumarate. Shown are post-contrast T1-weighted magnetization prepared 2 rapid acquisition gradient echo (MP2RAGE) (A, E) images, along with axial (B, F), sagittal (C, G), and coronal (D, F) slices from post-gadolinium magnetization prepared fluid attenuated inversion recovery (MPFLAIR) images. The yellow arrows indicate the location of a nodular focus of leptomeningeal contrast enhancement in all 3 planes and its expected location on MP2RAGE.

Figure 3. Examples of “spread/fill” type enhancing foci in multiple sclerosis

Images from a 53-year-old man with relapsing remitting multiple sclerosis (RRMS) treated with dimethyl fumarate (A–D) and a 58-year-old man with RRMS treated with glatiramer acetate (E–H). Shown are post-contrast T1-weighted magnetization prepared 2 rapid acquisition gradient echo (MP2RAGE) images (A, E), along with coronal (B, H) axial (C, G), sagittal (D, F), and coronal (D, F) slices from post-gadolinium magnetization prepared fluid attenuated inversion recovery (MPFLAIR) images. The yellow arrows indicate the location of an spread/fill focus of leptomeningeal contrast enhancement in all 3 planes and its expected location on MP2RAGE images. Note the spread of contrast to fill nearly the entire sulcal space as visualized in panels F and H. Panel G is an axial cut, in-plane with the horizontal component of this sulcus, demonstrating the horizontal spread of contrast in this profound example of spread/fill foci.

Figure 4. Example of a “nodular” focus in a healthy volunteer

Images from a 37-year-old healthy volunteer. Shown are axial T1-weighted post-contrast magnetization prepared 2 rapid acquisition gradient echo (MP2RAGE) (A) and axial (B), coronal (C), and sagittal (D) images from post-gadolinium magnetization prepared fluid attenuated inversion recovery (MPFLAIR). The yellow arrows indicate a location of leptomeningeal contrast enhancement in all 3 planes and its expected location on MP2RAGE.