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Quantitative susceptibility mapping in superficial hemosiderosis of the central nervous system
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Edité par CCSD ; Elsevier Masson -
International audience. A 19-year-old man with no relevant medical history except a high velocity head trauma a few years earlier was admitted in our institution for sudden onset binocular diplopia. Head-CT performed afteer the trauma was depicted as being normal. He complained of chronic headaches for about three years, with recent worsening and painkillers resistance. Clinical examination found binocular ophthalmoplegia with paresis of both abducens nerves. Non-contrast CT-scan and CT angiography of the circle of Willis were normal. Brain MRI acquisition was performed on a 3T magnet (Skyra, Siemens, Germany) with a 32-channel head coil and included a dual-echo Susceptibility Weighted Imaging (SWI), with the following parameters: TE1/TE2 = 20/40 ms, TR = 47 ms, GRAPPA = 2, voxel size = 1 × 1 × 1.5 mm, 88 slices). Conventional sequences showed a subtle distension of the perioptic subarachnoid spaces on coronal T2 sequence (not shown), and a linear loss of signal on pial surface of the lefte lateral fissure (Fig. 1a). Susceptibility-weighted imaging was performed in order to quantify the related susceptibility effeect, through the use of quantitative susceptibility mapping. Marked pial signal loss on T2-GRE and susceptibility-weighted imaging (SWI) was observed at the level of the brainstem, lefte lateral fissure, cerebellar folia (Fig. 1b-f). Phase image was retrieved from SWI acquisition and underwent laplacian unwrapping as well as background field removal using regularization-enabled SHARP algorithm. Finally, total variation using split Bregman [1] method enabled images conversion to quantitative susceptibility maps (QSM). Reported susceptibility values were standardized according to the observed cerebrospinal fluid susceptibility. In normal appearing gray matteer (Fig. 1g-h), the value was 0.009 ± 0.1 ppm, while in cortico-pial affeected areas, measured susceptibility was 0.24 ± 0.1 ppm (Fig. 1f), suggesting a paramagnetic effeect. Discrete atrophy of the superior cerebellar vermis was also noted (Fig. 1k). T2-weighted images of the spinal cord showed a low signal lining on the spinal cord, suggesting hemosiderin deposit (Fig. 1i-j). No acute subarachnoid bleeding was present. Neither MR angiography of the intracranial vessels nor spinal MRI revealed any vascular malformation. No intra-axial hemorrhage was found. Fundoscopic examination revealed bilateral papillary subedema that was confirmed by the fluorescein angiogra-phy showing late papillary dye leakage. Lumbar puncture was finally performed and showed severe intracranial hypertension (57 cmH 2 O, normal range 7-15 cmH 2 0). Neither erythrocytes nor xantochromia were present. The diagnosis of superficial siderosis of the central nervous system was made based on the symptoms that were supported by radiological findings. Discussion
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