Chapter 13 - MRI mimics of multiple sclerosis
Introduction
Magnetic resonance imaging (MRI) is highly sensitive for the detection of intracranial and spinal cord abnormalities, including the white-matter damage seen as hyperintense lesions on T2-weighted (T2WI) and fluid attenuated inversion recovery (FLAIR) images in patients with multiple sclerosis (MS). Although, in many cases, the characteristic lesion morphology, the patterns of distribution of lesions, or the involvement of specific anatomic structures can support the diagnosis of MS, it is important to bear in mind that many other disorders can present with a similar MRI appearance to MS, especially on T2WI/FLAIR images.
In a patient with symptoms suggestive of inflammatory demyelinating disease, the principal clinical objective is to exclude alterative non-demyelinating disorders and to distinguish MS from other idiopathic inflammatory demyelinating disorders. Together with a patient’s clinical history, examination, and laboratory findings, the MRI plays an important role in the exclusion of these alternative diagnoses. In this regard, the most common difficulty, by far, is to distinguish MS from acquired hypoxic/ischemic small-vessel disease (SVD) on the basis of its MRI appearance, especially in middle-aged or elderly patients. This is due to the high prevalence of SVD leukoencephalopathy in these age groups. Therefore, the first goal of this chapter is to emphasize those MRI features, which can be used to distinguish MS from hypoxic SVD. We will also discuss other less frequent acquired and inherited pathologic disorders that may affect white matter in a pattern similar to MS, both reviewing their most important imaging findings and identifying those MRI features which can be used to distinguish these diseases from MS. Advanced imaging techniques and high field strength (3 T) or ultra-high field strength (7 T) imaging may help to narrow the differential diagnosis but, because they are not routinely performed, we will focus on the use of conventional MRI sequences in the differential diagnosis of MS. Finally we will summarize those MRI findings which, if present, should suggest a diagnosis other than MS.
Section snippets
MRI in MS
Demyelination, inflammation, gliosis, and axonal damage are the main morphologic hallmarks in MS (Brück, 2005). On MRI, MS plaques are commonly seen as multiple focal lesions with intermediate to low-signal intensity on T1-weighted images (T1WI) and high-signal intensity on T2WI and FLAIR images. Initially, these lesions show sharp margins, although they tend to converge, especially in the periventricular regions, becoming less well defined at later stages. MS lesions occur bilaterally, but not
Diseases that may mimic the appearance of MS on MRI
Several acquired and inherited disorders can radiologically mimic MS. These will be considered in the context of several broad etiologic categories.
Differential diagnosis: practical tips
A practical approach to the interpretation of an MRI study with MS-like lesions involves a two-step process. The first is to exclude (if possible) the non-demyelinating disorders by evaluating carefully specific features of the white-matter lesions. These include symmetry/asymmetry, presence of confluent or focal lesions, location of lesions, involvement of the U-fibers, involvement of gray matter, presence of leptomeningeal enhancement, evidence of spinal cord lesions, and other “red flags,”
References (135)
- et al.
MRI and the diagnosis of multiple sclerosis: expanding the concept of “no better explanation”
Lancet Neurol
(2006) - et al.
MRI findings in osmotic myelinolysis
Clin Radiol
(2002) - et al.
Natalizumab-associated progressive multifocal leukoencephalopathy in patients with multiple sclerosis: lessons from 28 cases
Lancet Neurol
(2010) - et al.
Neuroimaging of mitochondrial disorders
Mitochondrion
(2004) - et al.
Late magnetic resonance imaging features of leukoencephalopathy in children with central nervous system tumours following high-dose methotrexate and neuraxis radiation therapy
Eur J Cancer
(2005) - et al.
MRI findings in neuro-Behçet's disease
Clin Radiol
(2001) - et al.
Long term follow-up of patients with post-infectious encephalomyelitis: evidence for a monophasic disease
J Neurol Sci
(1999) Cerebral small vessel disease: from pathogenesis and clinical characteristics to therapeutic challenges
Lancet Neurol
(2010)- et al.
Diffuse axonal injury in head injury: definition, diagnosis and grading
Histopathology
(1989) - et al.
Acute disseminated encephalomyelitis in children: outcome and prognosis
Neuropediatrics
(2003)