Susac Syndrome: Brain MRI findings in 3 patients at our institution and review of literature.

Transcription

1 Susac Syndrome: Brain MRI findings in 3 patients at our institution and review of literature. Poster No.: C-0395 Congress: ECR 2014 Type: Educational Exhibit Authors: H. Chaves, M. S. TORONCHIK, P. M. PFISTER, E. Triñanes, C. Rollan, C. Romero; Buenos Aires/AR Keywords: MR-Diffusion/Perfusion, MR-Angiography, MR, Vascular, Neuroradiology brain, CNS, Imaging sequences, Ischemia / Infarction DOI: /ecr2014/C-0395 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 15

2 Learning objectives To increase the awareness of this infrequent pathology. To highlight the importance of MRI studies in its diagnosis. To describe typical brain MRI findings in this syndrome, that differentiates it from other pathologies. Background Susac Syndrome (SS) is a rare disorder that is thought to be caused by autoimmunemediated occlusion of microvessels in the brain, retina and cochlea. These occlusions lead to a characteristic clinical triad of CNS dysfunction, visual disturbances due to branch retinal artery occlusions (BRAO), and hearing deficits. Brain MRI, retinal fluorescein angiography, and audiography are the key studies for an accurate diagnosis. Prompt immunosuppressive therapy is recommended to reduce morbidity. [1] Only 304 cases have been published since it was first described by J.O. Susac in [2] The disease has also been referred as SICRET (small infarctions of cochlear, retinal and encephalic tissue) and RED-M (microangiopathy with retinopathy, encephalopathy and deafness).[3] Brain MRI is fundamental for SS diagnosis, especially when encephalopathy symptoms such as headache, confusion, memory loss, behavioral changes, dysarthria and mutism are present.[4] Findings and procedure details Procedure Details We will describe the MRI findings of 3 patients evaluated at our institution in the period between June 2010 and June MRI scans were performed in 1.5 and 3.0 Tesla scanners. Our imaging protocol included diffusion weighted imaging (DWI), T1WI, T2WI, fluid attenuation inversion recovery (FLAIR), T2*WI and arterial 3D-TOF angiography. Findings Restrictive DWI lesions in the corpus callosum and internal capsule were found in 100% of our patients. Scattered focal lesions involving other white matter regions were also Page 2 of 15

3 found in all of them. Lesion enhancement was present in only one of the patients. No abnormalities were found on T2*WI. No lesions were found involving basal ganglia or thalamus. Infratentorial lesions were found in only one patient. No angiographic abnormalities were registered on 3D TOF. Literature Review MR images are invariably abnormal, particularly in encephalopathic onset patients. Adequate interpretation of the MRI should increase the diagnostic shield of SS. Main differential diagnosis are multiple sclerosis (MS) and acute disseminated encephalomyelitis (ADEM). [4] We will describe common and not so common brain MRI findings of SS in the different pulse sequences that guide us toward this diagnosis. DWI is a sequence in which the Brownian movement of water molecules can be quantified. If this movement is limited in all axes, it is said that the diffusion is restricted. ADC maps are also evaluated to confirm this restriction. Where a bright image is seen on DWI, a hypointense area should be seen on ADC maps. SS can have restrictive lesions involving mainly white matter (WM), due to arteriolar microinfarcts (Figure 1). DWI is useful in demonstrating the heterogeneous nature of the lesions. DWI is also important to differentiate T2 bright lesions from MS and ADEM, which usually don t have restricted diffusion.[5,6] Page 3 of 15

4 Fig. 1: Multiple focal restrictive lesions in DWI with involvement of the corpus callosum, internal capsule and subcortical white matter (top row). Corresponding ADC maps (inferior row). T2*WI isuseful in depicting blood products, helping to differentiate patients with vasculitic hemorrhagic lesions, as these were not reported in SS. Some studies suggest that magnetic susceptibility images at 7T will be able to differentiate MS plaques from SS lesions easily.[7] T2WI and FLAIR T2WI pulse sequences are the most sensitive to evaluate WM lesions in SS, being FLAIR T2WI the preferred one. WM lesions are more frequently found in the corpus callosum, periventricular WM, subcortical WM, centrum semiovale and internal capsule. FLAIR T2WI may also aid to the recognition of gray matter (GM) lesions (cortical or basal ganglia). When subcortical WM or GM lesions are suspected, double inversion recovery (DIR) pulse sequences should be used. (Figure 2) Page 4 of 15

5 Fig. 2: Axial DIR shows at least three subcortical white matter lesion, better depicted than on FLAIR. Page 5 of 15

6 Corpus callosum is always affected in SS. Callosal microinfarctions are the predominant findings and are best seen on sagital FLAIR T2WI. Microinfarcts prefer the central portion of the callosum and, depending on their visual appearance; they are referred as "snowballs" that eventually evolve into central callosal "holes" (Figure 3). The roof of the callosum is also frequently affected: microinfarcts here are referred as "icicle" and "spoke" configurations. The callosal-septal (ventricular) surface is infrequently involved, and only when there are also central callosal lesions. These characteristics allow us to differentiate SS lesions from the ones found in MS and ADEM. (Figure 4) Fig. 3: Sagital T1WI, shows the typical hypointense "holes" in the central portion of the corpus callosum in the three patients. Fig. 4: Sagital FLAIR T2WI shows callosal microinfarctions in the three patients. "Snowballs" are marked with sky-blue arrows, roof lesions in green, calloso-septal lesions in red and a "spoke" lesion is in purple. Page 6 of 15

7 Microinfarcts in the internal capsule results in a "string of pearls" configuration. This is most dramatically shown on DWI and is always accompanied by microinfarctions in the corpus callosum. The "string of pearls" may be seen on DWI before it is well seen on axial FLAIR sequences (Figure 5). The combination of typical central callosal lesions and "string of pearls" in the internal capsule is pathognomonic for SS.[1] Fig. 5: Axial DWI, Axial T2WI and Axial FLAIR T2WI shows classic microinfarcts in the internal capsule with a "string of pearls" pattern. T2WI can be superior to FLAIR in the characterization of cavitated chronic lesions (Figure 6). DWI can also be superior to FLAIR in depicting small punctiform infratentorial lesions (Figure 7). Page 7 of 15

8 Fig. 6: Axial T2WI shows cavitated lesions involving the corpus callosum and paraventricular WM. Fig. 7: Axial DWI shows multiple punctiform infratentorial lesions. Three-dimensional time-of-flight magnetic resonance angiography (3D TOF) is acquired by using a radio-frequency spoiled gradient-echo sequence which allows multidirectional Page 8 of 15

9 visualization. In the Susac syndrome the angiography is usually normal because it is believed to affect only the precapillary arterioles (#100 µm in diameter) being bellow the resolution of the 3D TOF. [7] After the administration of Gadolinium, SS lesions may enhance in acute or subacute stages. Leptomeningeal enhancement has also been reported close to a lesion. These are both nonspecific findings and may be seen in different clinical scenarios. (Figure 8) Fig. 8: Axial T2 FLAIR, Axial T1 y Axial T1 post-contrast MR images that show a paraventricular lesion with enhancement. Images for this section: Page 9 of 15

10 Fig. 1: Multiple focal restrictive lesions in DWI with involvement of the corpus callosum, internal capsule and subcortical white matter (top row). Corresponding ADC maps (inferior row). Page 10 of 15

11 Fig. 2: Axial DIR shows at least three subcortical white matter lesion, better depicted than on FLAIR. Page 11 of 15

12 Fig. 3: Sagital T1WI, shows the typical hypointense "holes" in the central portion of the corpus callosum in the three patients. Fig. 4: Sagital FLAIR T2WI shows callosal microinfarctions in the three patients. "Snowballs" are marked with sky-blue arrows, roof lesions in green, calloso-septal lesions in red and a "spoke" lesion is in purple. Page 12 of 15

13 Fig. 5: Axial DWI, Axial T2WI and Axial FLAIR T2WI shows classic microinfarcts in the internal capsule with a "string of pearls" pattern. Fig. 6: Axial T2WI shows cavitated lesions involving the corpus callosum and paraventricular WM. Page 13 of 15

14 Fig. 7: Axial DWI shows multiple punctiform infratentorial lesions. Fig. 8: Axial T2 FLAIR, Axial T1 y Axial T1 post-contrast MR images that show a paraventricular lesion with enhancement. Page 14 of 15

15 Conclusion MRI is one of the three keystones that support the diagnosis of Susac Syndrome, especially when encephalopathy symptoms are present. Knowledge of typical imaging patterns and their differential diagnosis is fundamental for a prompt treatment. Personal information References Rennebohm R, Susac JO, Egan RA, Daroff RB. Susac's Syndrome-update. J Neurol Sci Dec 15;299(1-2): Susac JO, Hardimann JM, Selhorst JB. Microangiopathy of the brain and retina. Neurology 1979;29: Dörr J, Krautwald S, Wildemann B, Jarius S, Ringelstein M, Duning T, et al. Characteristics of Susac syndrome: a review of all reported cases. Nat Rev Neurol Jun;9(6): Susac JO, Murtagh FR, Egan RA, Berger JR, Bakshi R, Lincoff N, et al. MRI findings in Susac's syndrome. Neurology Dec 23;61(12): White ML, Zhang Y, Smoker WR. Evolution of lesions in Susac syndrome at serial MR imaging with diffusion-weighted imaging and apparent diffusion coefficient values. AJNR Am J Neuroradiol May;25(5): White ML, Zhang Y, Smoker WRK. Evolution of Lesions in Susac Syndrome at Serial MR Imaging with Diffusion-Weighted Imaging and Apparent Diffusion Coefficient Values. AJNR Am J Neuroradiol.2004;25: Wuerfel J, Sinnecker T, Ringelstein EB, Jarius S, Schwindt W, Niendorf T, et al. Lesion morphology at 7 Tesla MRI differentiates Susac syndrome from multiple sclerosis. Mult Scler. 2012;18(11): Do TH, Fisch C, Evoy F. Susac syndrome: report of four cases and review of the literature. AJNR Am J Neuroradiol 2004;25: Page 15 of 15