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Neuroradiology Case of the Week

Case 108

Deepa Popuri, Leena Ketonen, MD, PhD,
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 39-year-old man with history of right upper extremity and right face numbness and weakness.

Radiological Findings: Two focal areas of high T2 signal are noted within the cervical spinal cord.  One occurs at the craniocervical junction in the right posterior central spinal cord measuring 14 mm (craniocaudal).  A second smaller lesion is in the right lateral spinal cord, posterior to C3.  These areas are consistent with areas of demyelination. 
     There is mild degenerative disc disease with minimal neural foraminal narrowing at the right C6-7 level.

Diagnosis: Multiple sclerosis of cord

Discussion:
Clinical Discussion:
Epidemiology:
     Multiple sclerosis (MS) is the most common demyelinating disease. Although it occurs worldwide in different racial groups and geographic locations, it is most common in young adults ages 20-40 and in Northern European or temperate areas. Disease is more common in females than males, especially in the children and adolescent age group [1].
Presentation:
     Peak symptom presentation typically occurs in third and fourth decades of life. Most acute symptoms are from cord lesions rather than brain lesions [1,2]. Spinal cord involvement in multiple sclerosis usually leads to sensory and motor deficits, bladder and bowel dysfunction, gait disturbances, and ataxia [3]. There is correlation between severity of cord abnormalities and physical disabilities. Presentation of symptoms is variable, with most patients exhibiting relapsing remitting MS. These patients may then shift to the chronic progression phase of the disease. The very rare Marburg type of MS is associated with rapid death and high mortality [1,2].
Etiology/Pathology:
     The exact etiology of MS is unknown although a genetic basis of autoimmune demyelination is the most favored theory. The animal model of MS has shown that peptides derived from myelin basic protein presented on class II major histocompatibility stimulates T helper cell response. These self-antigens are most likely derived from viral infection. The genetic basis of MS is supported by the fact that first degree relatives of MS patients show subclinical degrees of demyelination [1].
     MS lesions, also called plaques, involve the destruction of myelin and myelin producing oligodendrocytes, and axonal loss. Plaques are characterized by necrosis, atrophy, and cyst formation, with rare occurrences of hemorrhage and calcification. Active lesions exhibit macrophage infiltration and mild perivascular inflammation while inactive lesions demonstrate pronounced astrogliosis [1].
     Multiple lesions in the brain and spinal cord are common, although large solitary lesions occur. Extension of periventricular lesions into deep white matter are referred to as “Dawson’s fingers”. Involvement of the corpus callosum is also common. Posterior fossa lesions occur in less than 10% of adult MS cases, but are more common in children [1].
     Approximately 75% of MS cases involve spinal cord lesions. Atrophy results in reduction of cord cross section. The spinal cord may be earliest affected site in onset of MS. Early disease may be confined to the cervical cord while plaques become more evenly distributed throughout the cord in later stages.  Cord lesions do not always accompany brain lesions; plaques in the Devic variant of MS are confined to the optic nerve and spinal cord [1].     

Neuroimaging Discussion:
     MR imaging has 85% sensitivity in the detection of MS lesions. Most foci are clinically silent and therefore there is poor correlation with presentation of symptoms. Cord lesions are not necessary for diagnosis of MS. Patients with suspicion of demyelinating disease should be evaluated for brain lesions. If there are no abnormal brain findings, a spine study is indicated to evaluation for plaques in the cord.
     Brain plaques appear isotense to hypotense on T1WI and hyperintense of T2WI. Most lesions do not enhance, although it is possible for lesions to be visualized on contrast enhanced T1WI that were not seen on T2WI. Enhancement represents disruption of blood brain barrier and may appear solid or ring shaped. Transient enhancement will occur during active demyelinating process [1].
     Cord lesions appear elongated and hyperintense on T2WI. Unlike brain lesions, they are less likely to appear hypotense on T1WI. There may be focal or generalized cord atrophy, resulting in decreased cross sectional area of cord. Enhancement in the cord occurs less than in the brain and may be patchy [1,2].
     Fast TI inversion recovery (FSTIR) images prolongs T1 and T2 relaxation times and offers greater lesion/white matter contrast than spin echo or fast spin echo. This is useful in the evaluation of MS cord lesions since these have greater T1 and T2 relaxation times than white matter. Despite fat suppression capabilities and improved sensitivity in detection of multiple cord lesions, there is more noise and CSF motion artifact than spin echo techniques [3,4]. Filippi reports that FSTIR may detect as many as 66% more spinal cord lesions than T2WI [5].
     Since patients are often asymptomatic, serial studies are important in monitoring progression of MS.T2WI gives no information regarding degree of axonal loss or demyelination in the spinal cord. Magnetization transfer ratio histogram (MTR) and decreases in NAA in MR spectroscopy provide information regarding degeneration of axonal membrane and demyelination in the brain. MTR and MR spectroscopy brain studies are more useful parameters in correlation to physical disability than T2WI [5,6].

References:

1. Osborn A. Diagnostic Neuroradiology. St. Louis: CV Mosby, 1994.
2. Rocca MA, Mastronardo G, Horsfield MA, et al. Comparison of three MR sequences for the detection of cervical cord lesions in patients with multiple sclerosis. AJNR 1999;20:1710-1716.
3. Bashir K, Cai CY, Moore TA, et al. Surgery for cervical spinal cord compression in patients with multiple sclerosis. Neurosurgery 2000;47:637-642.
4. Thorpe JW, MacManus DG, Kendall BE, et al. Short tau inversion recovery fast spin-echo (fast STIR) imaging of the spinal cord in multiple sclerosis. Magnetic Resonance Imaging 1995;12:983-9.
5. Filippi, M. Bozzali ZM, Horsfield MA. A conventional and magnetization transfer MRI study of the cervical cord in patients with MS. Neurology 2000;54:207.
6. Stevenson VL, Leary SM, Losseff NA, et al. Spinal cord atrophy and disability in MS: a longitudinal study. Neurology 1998;51:234-238.