From the Guidelines
A multiple sclerosis (MS) lesion is an area of focal hyperintensity on a T2-weighted or proton density-weighted sequence, typically round to ovoid in shape, and at least 3 mm in diameter.
Key Characteristics of MS Lesions
- They are usually visible on at least two consecutive slices to exclude artefacts or small hyperintensities
- MS lesions tend to affect specific white matter regions, such as the periventricular and juxtacortical white matter, the corpus callosum, infratentorial areas, and the spinal cord
- They can be gadolinium-enhancing, which plays an important role in evaluating patients suspected of MS, and can support dissemination in time when it occurs in some lesions but not others
Location and Distribution of MS Lesions
- MS lesions typically develop in both hemispheres, but their distribution is often mildly asymmetric in the early stages
- They can occur in any CNS region, but are more common in specific areas such as the periventricular and juxtacortical white matter
- In the spinal cord, MS lesions are often small, covering less than two vertebral segments, and usually less than half of the cord area, and are typically located in the periphery of the spinal cord, mainly in the lateral or dorsal columns
Red Flags for MS Lesions
- Longitudinally extensive lesions extending over three or more vertebral segments
- Prominent involvement of the central grey matter
- Swelling of the spinal cord
- Leptomeningeal or nerve root involvement
- Cavitation or evidence of micro/macrobleeds As noted by 1, the definition of an MS lesion is based on its appearance on MRI, and the location and distribution of lesions can help support a diagnosis of MS. Additionally, 1 highlights the importance of considering the specific characteristics of each individual lesion, as well as the overall patterns of lesions, to support the diagnosis of MS or other conditions. Furthermore, 1 discusses the role of gadolinium enhancement in evaluating MS lesions, and 1 and 1 provide guidance on the interpretation of spinal cord lesions in MS.
From the Research
Definition of Multiple Sclerosis Lesions
A multiple sclerosis (MS) lesion is characterized by:
- Focal demyelination
- Inflammation
- Scar formation
- Variable axonal destruction 2 MS lesions can occur in both white and grey matter, with different pathological characteristics:
- White matter lesions (WMLs) are pathologically characterized by the presence of immune cells that infiltrate the CNS 3
- Grey matter lesions (GMLs) are less inflammatory, with less macrophage and lymphocyte infiltration, and are associated with significant axonal transection and neuronal loss 4
Pathological Characteristics
The pathological hallmarks of MS lesions include:
- Demyelination
- Inflammation
- Axonal damage
- Glial cell activation 5 The nature of the soluble factors responsible for demyelinating activity in MS is currently undefined, but it is thought that inflammation drives tissue injury at all stages of the disease 5
Types of MS Lesions
There are different types of MS lesions, including:
- White matter lesions (WMLs)
- Grey matter lesions (GMLs)
- Cortical lesions, which can extend inward from the surface of the brain and are often underestimated by standard histochemical myelin staining methods 4
- Subpial demyelination, which can occur in all cortical areas of the brain and is associated with the progressive phases of disease 4
Clinical Significance
The clinical significance of MS lesions is not yet fully understood, but it is thought that they contribute to the development of symptoms and disability in MS patients: