Clinical diagnosis
Case 184
【Progress】
He was carried to mother-children central hospital to get more intensive care service.
【Discussion】
There are five types of influenza-associated encephalopathy visualized on brain MRI: acute necrotizing encephalopathy, posterior reversible encephalopathy syndrome, mild encephalopathy with a reversible splenium lesion, acute hemorrhage encephalopathy, meningoencephalitis (1-4).
Acute necrotizing encephalopathy of childhood (ANEC) is known to be poor prognostic; approximately 82% patients are aged less than 5 years, mortality rate is approximately 30 %, complete recovery 10 % and neurological sequelae remains in survivors (1). Pathogenesis of ANEC is unclear but considered to be a storm of cytokines rather than virus infection itself (5). Typical images on MRI were symmetric necrosis of bilateral thalamus. Basal ganglion, cerebellum and brain stem could be damaged. ANEC pathologically composes of cytotoxic edema, vasogenic edema and hemorrhagic necrosis. MRI with diffusion weighted imaging show high signal intensity corresponded to cytotoxic edema of the lesion, indicating low values on ADC map. T2* MRI show low signal intensity corresponded to hemorrhagic lesion (6, 7).
Posterior reversible encephalopathy syndrome (PRES) is visualized on MRI as confluent high signal intensity of posterior area on FLAIR or T2WI and slightly high signal intensity due to T2 shine through on DWI and high signal intensity on ADC maps, indicating vascular edema. The pathogenesis of PRES is vasogenic edema due to hypertension or endothelial disorder (8). Vertebral artery dose not have pressure receptor, while internal carotid artery has it at carotid sinus. Then, sudden high blood pressure or clamps causes vascular edema at the territory of vertebral artery. PRES is reported to occur associated with ANEC (8).
Meningoencephalitis is also accompanied with ANEC. It is considered that meningoencephalitis occurs infecting from cerebrospinal fluids.
Mild encephalitis with a reversible splenic lesion (MERS) appears clinical symptoms of conscious disorder, clamps, abnormal behavior within one week after high fever and recovers within 10 days without sequela. Diffusion weighted (DW) MRI show features of high signal intensity on whole splenium sometimes expanded to deep white matter. It disappears within one week and remains no abnormal signal intensity and no atrophy (9, 10). ADC map shows low values corresponded to high signal intensity on DWMRI, indicating cytotoxic edema and different from PRES with vasogenic edema. Because corpus callosum genu sometimes is damaged, MERS occurrence does not relate with arterial blood supply. Pathogenesis of MERS is unclear but it is considered that immune response is related to axon and/or envelope of corpus callosum splenium during virus infection (9, 10).
In our case, the following day after high fever due to influenza A, DWMRI showed high signal intensity corresponded to not only corpus callosum splenium but corpus callosum genu and deep white matter.
【Summary】
We present an eight-year-old boy for consciousness disorder, high fever and abnormal behavior. He was diagnosed influenza A at local clinic before coming to our hospital. Brain MRI with diffusion weighted imaging showed high signal intensity symmetrically at corpus callosum splenium and genu, and deep white matter. Apparent diffusion coefficient map showed low values, indicative of cytotoxic edema, compatible with diagnosis mild encephalitis with a reversible splenium lesion (MERS). It is borne in mind that influenza associated encephalopathy includes acute necrotizing encephalopathy of childhood (ANEC), posterior reversible encephalopathy syndrome (PRES), acute hemorrhage encephalopathy, meningoencephalitis and MERS. Typical images on MRI of ANEC were symmetric necrosis of bilateral thalamus. Prognosis of ANEC is poor: mortality rate is approximately 30 %, complete recovery 10 % and neurological sequelae remains in survivors. PRES, hemorrhagic encephalitis and meningoencephalitis are associated with ANEC. The images of PRES appear vasogenic edema on MRI. Meanwhile, prognosis of MERS is relatively good although MRI with DWI shows cytotoxic edema corresponded to corpus callosum splenium.
【References】
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8.Bartynski WS, et al. Posterior reversible encephalopathy syndrome (PRES) and cerebral vasculopathy associated with influenza A infection: report of a case and review of the literature. J Comput Assist Tomogr 2009;33:917–22
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2020.3.18