Abstract
Susceptibility-weighted magnetic resonance imaging (MRI) (SWI) offers additional information on conventional MRI contrasts. Central veins can be identified within lesions, and recently, it has been suggested that multiple sclerosis (MS) lesions with slowly expanding demyelination, so-called smoldering lesions, can be identified by a phase rim surrounding the lesion. We analyzed post-contrast SWI in regard to intrinsic lesion characteristics in a cohort of MS patients. A total of 294 MS patients were evaluated using a 3-T MRI. A comprehensive MRI protocol was used including post-contrast SWI. Lesions of at least 5 mm in size were analyzed on conventional MRI and SWI with a structured reporting scheme with a focus on SWI lesion characteristics. A total of 1,323 lesions were analyzed: 1,246/1,323 (94%) were non-enhancing and 77/1,323 (6%) were contrast-enhancing (CE) lesions. In CE lesions, the following patterns were seen: contrast enhancement was nodular in 34/77, ring-shaped enhancement was present in 33/77, and areas of peripheral enhancement were present in 10/77. In CE lesions, an association with central veins was found in 38/77 (50%). In 75/1,246 (6%) non-enhancing lesions, a central dark dot in keeping with a central vein was seen, whereas 162/1,246 (13%) showed peripheral hypointense dots/rims, 199/1,246 (16%) showed scattered hypointense dots mainly within the lesion area, and in 374/1,246 (30%), no SWI hypointensity was detected. Furthermore, 436/1,246 (35%) lesions showed isointensity to the surrounding tissue and were not visible on SWI. SWI is able to offer additional aspects of MS pathology also when used after the application of a contrast agent. Veins connected to lesions, a potentially useful marker in the differential diagnosis of MS, were seen in about 50% of enhancing lesions. Susceptibility artifacts, suggested to mark the presence of myelin-laden macrophages and smoldering inflammation, were visible in 28% of lesions as hypointense dots in and in the periphery of the lesion. Given those results, SWI may provide practical useful additional information in the evaluation of the lesion status in MS patients.
Highlights
Conventional magnetic resonance imaging (MRI) techniques play an important role in the diagnosis and monitoring of disease evolution in multiple sclerosis (MS)
In the subgroup of the 10 patients examined with susceptibility-weighted imaging (SWI) before and after contrast agent injection, we identified 35 nonenhancing lesions: 6/35 lesions were homogenously hypointense without dark susceptibility dots, 7/35 showed ring-shaped distribution of susceptibility dots, 5/35 showed scattered distribution of susceptibility dots, 2/35 showed a central dot suggestive of a central vein, and 15/35 were not visible on Homogenous hypointense lesions
We limited the analysis of SWI characteristics to lesions of at least 5 mm in diameter in order to be able to differentiate intrinsic lesion characteristics
Summary
Conventional magnetic resonance imaging (MRI) techniques play an important role in the diagnosis and monitoring of disease evolution in multiple sclerosis (MS). The susceptibility effects in those lesions are due to the presence of iron-laden activated microglia/macrophages and reactive astrocytes at the lesion edge [6, 8,9,10,11, 13]. These lesions have been suggested to represent areas of so-called smoldering inflammation [10, 11, 13]. It has been demonstrated that these lesions may increase in size during longer observation periods Such gradual slowly evolving increases in lesion size can be identified when analyzing serial T1w MRI as it has recently been demonstrated [14]. This type of lesion has generated high clinical interest, as it is conceivable that it contributes to gradual clinical worsening in MS
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