Understanding the Role of the Choroid Plexus in Multiple Sclerosis as an MRI Biomarker of Disease Activity

The choroid plexus (CP) is an organoid structure located in the ventricles of the brain that produces CSF and serves as a port of entry for lymphocytes into the CNS. In multiple sclerosis (MS), the CP acts as an important modulator and target of inflammatory activity, as shown in postmortem studies.^1-3 Recently, new evidence has emerged highlighting the importance of in vivo CP measurements for understanding MS pathogenesis. The first study, published in 2020, showed gadolinium enhancement in the CP of patients with MS who had recently experienced a clinical relapse.⁴ Subsequent work demonstrated that CP volume was larger in patients with RRMS than in healthy controls, particularly in those with radiologically active disease, in whom it also correlated with clinical relapses.⁵ Clinical relevance of the finding was suggested when it was shown that CP volume correlated with the expanded disability status scale (EDSS).⁶ CP volume also predicted future EDSS development over a follow-up of 4 years, more than conventional MRI markers, such as the number of T2 or gadolinium-enhancing lesions at baseline. The enlargement of the CP is MS-specific because it was not observed in patients with neuromyelitis optica spectrum disorder or migraine.⁷ Most recently, CP enlargement in MS was associated with the expansion of chronic lesions and lesion severity measured with diffusion MRI⁸ and with remyelination failure in periventricular areas quantified with ¹¹C-PiB-PET.⁹