Choroid Plexus Cysts on 7T MRI Differentiate NMOSD from MS

Abstract Background Multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) share overlapping clinical and imaging features, complicating differential diagnosis. The choroid plexus is increasingly recognized as a regulator of neuroinflammation and may play a critical role in the pathogenesis and differentiation of these conditions. Choroid plexus cysts (CPCs) are difficult to detect with conventional MRI resolution and standard anatomical approaches. High-resolution 7T MRI enables their visualization as readily identifiable and quantifiable morphological changes, offering a new direction for choroid plexus research. Objective To characterize choroid plexus cysts (CPCs) in aquaporin-4 antibody–positive NMOSD and relapsing–remitting MS (RRMS) using ultra–high-field 7T MRI. Methods Fourteen patients aged 16–30 years were prospectively recruited, including seven NMOSD (mean age 22.9 years) and seven MS (mean age 22.1 years). CPCs were assessed on UHR-T2WI-TSE images for number, maximum/minimum diameter, and cross-sectional area. Conventional brain lesions were evaluated on T2-FLAIR. Independent readings by two radiologists were adjudicated by a senior neuroradiologist. Results CPCs were present in all NMOSD patients (7/7) but only 57% of MS patients (4/7). Compared with MS, NMOSD showed a higher CPC burden with greater counts (median 4 vs 1; p=0.037) and non-significant trends toward larger diameters and areas (maximum diameter 4.17 mm vs 2.27 mm; minimum diameter 3.58 mm vs 1.82 mm; cross-sectional area 4.41 mm2 vs 2.02 mm2; p=0.072–0.095). Both groups demonstrated right-sided predominance. In contrast, brain lesions were more prevalent in MS (7/7) than in NMOSD (3/7; p=0.015). Conclusions 7T MRI reveals distinct CPCs characteristics in NMOSD and MS. Despite fewer brain lesions in NMOSD compared with MS, CPCs burden remained consistently higher. These findings suggest that CPCs may represent a more sensitive and quantifiable structural change, serving as a potential imaging-biomarker for distinguishing NMOSD from MS. Validation in larger cohorts is warranted to advance understanding of neuroimmunological diseases and to clarify the role of CPCs in neuroinflammation. Key point Identifying additional differences in brain injury between NMOSD and MS is crucial for diagnosis and therapy. CPCs are more prevalent and distinct in NMOSD than in MS, unveiling an “iceberg” of structural pathology hidden at conventional imaging resolution. CPCs are readily identifiable and quantifiable, indicating their potential as a novel imaging biomarker for differential diagnosis in clinical practice.