British Journal of Radiology (2006) 79, e28-e31
© 2006 British Institute of Radiology
doi: 10.1259/bjr/36636301
Diffusion-weighted imaging findings in Balo concentric sclerosis
E C Kavanagh, MRCPI, FFR, RCSI,
M K S Heran, MD,
D M Fenton, MD,
J S Lapointe, MD,
R A Nugent, MD and
D A Graeb, MD
Division of Neuroradiology, Department of Radiology, Vancouver General Hospital, 899 West 12th Avenue, Vancouver, British Columbia, V5Z 1M9, Canada
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Abstract
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Balo concentric sclerosis is a rare demyelinating disease. Pathognomonic features have been previously described. Diffusion-wighted imaging findings have not been previously described in Balo concentric sclerosis. We describe the diffusion-weighted imaging findings in a 45-year-old lady with Balo concentric sclerosis. Diffusion-weighted imaging offers insight into the possible pathophysiology of this rare disease.
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Introduction
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Balo concentric sclerosis is an uncommon demyelinating disorder, believed to be a variant of multiple sclerosis [1, 2]. Imaging features pathognomonic for Balo concentric sclerosis include alternating rings of demyelinated and myelinated white matter seen on T2 weighted images with concentric ring enhancement on T1 weighted images post-administration of gadolinium [2]. We describe the diffusion-weighted MRI findings in a 45-year-old woman with Balo concentric sclerosis.
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Case report
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A 45-year-old, right handed lady presented with a 1 month history of intermittent right arm weakness and slurred speech. Motor and reflex examinations were normal. A non-contrast CT scan performed at another institution had suggested the presence of an infarct in the left corona radiata. An MR of the brain was then performed which revealed a lesion in the left posterior corona radiata with multiple concentric rings of T2 hyperintensity (Figure 1a
). The central core of the lesion showed high signal on diffusion-weighted images, consistent with T2 shine-through. The intervening ring showed evidence of unrestricted diffusion (Figure 1b,c). The outer ring showed evidence of mildly restricted diffusion in its most anterior aspect (Figure 1c, arrow), with an apparent diffusion coefficient (ADC) value of 0.84x10–3 mm2 s–1, while the remainder of this ring demonstrated T2 shine-through. The calculated ADC values were 1.38x10–3 mm2 s–1 for the central core, 1.33x10–3 mm2 s–1 for the remainder of the outer ring and 2.40x10–3 mm2 s–1 for the intervening ring of unrestricted diffusion. The ADC value in the posterior corona radiata of the normal contralateral hemisphere measured 1.01x10–3 mm2 s–1. Mild concentric enhancement was seen post-administration of gadolinium.
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Figure 1. A 45 year-old lady with Balo concentric sclerosis. (a) Axial T2 weighted image shows a lesion in the posterior left corona radiata with concentric rings of T2 hyperintensity. (b) Axial diffusion-weighted (b1000) image shows high signal within the centre and periphery of the lesion. An intervening ring of relatively unrestricted diffusion is seen. (c) Axial apparent diffusion coefficient map confirms the presence of restricted diffusion within the most anterior aspect of the outer ring (arrow). The intervening ring of relatively unrestricted diffusion is also confirmed.
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The patient was commenced on a course of oral steroids and her neurological symptoms improved after 2 weeks of therapy. A repeat MR performed 7 months later showed marked reduction in size of the lesion (Figure 2a). The previously noted areas of T2 shine-through had almost completely resolved (Figure 2b,c). The ADC value for the entire lesion was 0.94x10–3 mm2 s–1.
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Figure 2. A 45-year-old lady with Balo concentric sclerosis (MRI performed 7 months after Figure 1 ). (a) Axial T2 weighted image shows reduction in size of the previously identified lesion in the posterior left corona radiata. (b) Axial diffusion-weighted image shows some residual ill-defined high signal in the lesion, consistent with T2 shine-through. (c) Axial apparent diffusion coefficient map shows no evidence of restricted diffusion.
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Discussion
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Many case reports of Balo concentric sclerosis exist in the medical literature [1–6]. Historically the diagnosis was made post mortem and, until recently, Balo concentric sclerosis was believed to be a rapidly progressive and invariably fatal disease [3]. MRI can allow for this diagnosis to be made early, thus allowing appropriate therapy to be commenced. Corticosteroids have been shown to be effective in treating the neurological deficits associated with Balo concentric sclerosis [4].
The pathogenesis of this disease has been a topic of much debate within the pathology literature. Various theories exist as to the development of the typical findings of alternating zones of myelinated and demyelinated white matter. It has been proposed that these bands may represent areas of remyelination at the borders of areas of successive acute demyelination [5]. Others have postulated that the partially myelinated bands may represent the early stages of acute demyelination, rather that remyelination.
Pathognomonic MRI features in Balo concentric sclerosis have been proposed [2]. These features include alternating bands of demyelinated and myelinated white matter seen on T2 weighted images and the presence of concentric ring enhancement on T1 weighted images post-administration of gadolinium. MR spectroscopy demonstrated an increased choline peak and a decreased N-acetyl aspartate peak in one reported case of Balo concentric sclerosis [1]. Diffusion-weighted imaging findings in Balo concentric sclerosis have not been previously described. MRI findings are variable in patients with multiple sclerosis and lesions may appear hyperintense, isointense or hypointense on diffusion-weighted sequences [7, 8]. High signal on diffusion-weighted images in multiple sclerosis has been ascribed to T2 shine-through, making interpretation of apparent diffusion coefficient maps important. In our case, the high signal on diffusion-weighted images in the anterior aspect of the outermost ring truly represented restricted diffusion as shown on the apparent diffusion coefficient map. Restricted diffusion of free water has been described in areas of vacuolization and rapid demyelination [8]. The area of restricted diffusion seen in the anterior aspect of the lesion in this case may represent an area of active demyelination. This area did not show evidence of significantly restricted diffusion 7 months later. The concentric ring of unrestricted diffusion likely represents an area of encephalomalacia secondary to demyelination. The central core of the lesion showed high signal on the T2 and diffusion-weighted images, without evidence of ADC abnormality, consistent with T2 shine-through. The central core showed less T2 hyperintensity on follow-up and likely represents an area demyelinated white matter, without established encephalomalacic change. In this case more concentric rings were seen on T2 weighted images than on the diffusion-weighted images. T2 weighted sequences have higher spatial resolution than diffusion-weighted images and the smaller rings seen on T2 weighted images are likely to be beyond the resolution of the diffusion-weighted sequences. The underlying pathophysiological explanation for the concentric rings seen in cases of Balo concentric sclerosis remains unknown, but it is likely that the various rings represent different stages of demyelination, a theory that is supported by the diffusion-weighted findings shown here.
In this case report we have demonstrated the diffusion-weighted imaging findings in Balo concentric sclerosis. Diffusion-weighted imaging offers insight into the possible pathophysiology of this unusual manifestation of multiple sclerosis.
Received for publication June 1, 2005.
Revision received July 12, 2005.
Accepted for publication July 19, 2005.
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References
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- Karaarslan E, Altintas, A, Senol U, Yeni N, Dincer A, Bayindir C, et al. Balo's concentric sclerosis: Clinical and radiologic features of five cases. AJNR Am J Neuroradiol 2001;22:1362–7.[Abstract/Free Full Text]
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Abstract
Introduction
