NeuroradiologyE2860. Susceptibility Weighted Imaging: Beyond the Bleed
Palmer G, Baheti A, Patel S, Mukherjee S, Donahue J. University of Virginia, Charlottesville, United States
Address correspondence to G. Palmer (email@example.com)
Background Information: Susceptibility weighted imaging (SWI) is a high-resolution gradient echo MRI sequence that is created by combining magnitude and filtered-phase information. In neuroimaging, it has proven applications in evaluating hemorrhagic complications of ischemia, traumatic brain injury, and intratumoral hemorrhage. We educate about the uses of SWI outside the realm of hemorrhage that can be applied in clinical practice.
Educational Goals/Teaching Points: There are multiple examples of nonhemorrhagic pathology that can be evaluated using SWI. We divide these diagnoses into separate categories and, using a case-based approach, briefly describe the associated SWI findings in each diagnosis. These include metabolic (hemochromatosis), neurodegenerative (neurodegeneration with brain iron accumulation, brain death) pediatric (hypoxic ischemic injury, vein of Galen [VOG] malformation including high flow versus low flow vascular malformations), and miscellaneous (cavernous malformation, fat emboli, progressive multifocal leukoencephalopathy [PML], multiple sclerosis, and cerebral abscess).
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Several examples of nonhemorrhagic pathology and their associated unique SWI findings identified in cases are presented. Hemochromatosis is shown as magnetic susceptibility involving the choroid plexus with no calcium deposition seen on a recent head CT of the same patient. This confirmed mineral (iron) deposition of the choroid plexus is compatible with hemochromatosis. Neurodegeneration with brain iron accumulation (NBIA) is extensive susceptibility involving the lentiform nucleus as well as the caudate nucleus. All NBIA disorders demonstrate iron deposition in the globus pallidus. However, they differ in other areas of iron deposition and other associated findings. A large VOG malformation is identified within a pediatric patient. Several of the vessels within the malformation were hyperintense on SWI. This confirms the presence of high flow due to time-of-flight effects and lack of T2* effects without having to use contrast. In the study of brain death, SWI shows multiple branching hypointensities extending through both cerebral hemispheres parallel and perpendicular to the outer wall of both lateral ventricles (transcerebral vein sign) as well as hypointensities in both cerebral hemispheres and cortical areas (bilateral cortical vein sign). Both signs have been found to be associated with brain death.
Conclusion: SWI demonstrates utility in diagnosis of multiple pathologies outside the realm of intracranial hemorrhage. Familiarity with these pathologies as well as the technique and sequences will allow for quicker diagnosis and treatment while decreasing unnecessary subsequent imaging and tests.