Neuroradiology DOI 10.1007/s00234-014-1337-z
LETTER TO THE EDITOR
Respiratory syncytial virus-related encephalitis: magnetic resonance imaging findings with diffusion-weighted study Fuldem Yildirim Donmez
Received: 15 January 2014 / Accepted: 28 January 2014 # Springer-Verlag Berlin Heidelberg 2014
Dear Editor, I have read the article “Respiratory syncytial virus-related encephalitis: magnetic resonance imaging findings with diffusion-weighted study” by Park, A. et al. with interest . The authors aim to describe the diffusion-weighted imaging (DWI) findings, which showed normal results. As far as I could understand, the DWI showed no increased diffusion as well as no restriction. This is interesting because apart from the prognosis, there may be either restriction due to lymphocytic infiltration which is more common or increased diffusion Fig. 1 There is extensive edema on the temporal lobe extending to the insula on T2-weighted coronal image (a). There is hyperintensity on DWI (b, d) but ADC maps (c, e) do not show hypointensity compatible with cytotoxic edema; hence, they show subtle hyperintensity which may be seen in the subacute phase
F. Y. Donmez (*) Department of Radiology, Baskent University Faculty of Medicine, 44. Sokak No:11/8, Bahcelievler, Ankara, Turkey e-mail: [email protected]
due to vascular congestion, generalized, or local edema in cases of encephalitis . The prognosis may be poor in cases which show diffusion restriction, but good outcome can also be seen in cases with increased diffusion as well as in patients with no diffusion abnormality such as in this study group; the most important point for good prognosis is the absence of cytotoxic edema which affects gray matter neurons. Timing is important in imaging of patients with encephalitis as the pathology itself is very dynamic, especially in the pediatric group. The reason of the normal DWI may be related
Neuroradiology Fig. 2 There is increased signal at the level of insula bilaterally on FLAIR (a), which is normal on DWI (b) and increased signal on ADC map (c), compatible with the chronic phase
to the time of the imaging. In the very acute phase, restricted diffusion is due to perivascular cuffing and thrombus formation; in the subacute phase, these changes start to diminish and ADC values increase; and in the chronic phase, necrosis and demyelination cause higher ADC values . DWI is superior to conventional MRI in detecting early changes; however, when there is a time delay between the onset of the disease and imaging, DWI may be less sensitive . We had two patients with encephalitis recently. First patient was a 44-year-old woman who had headache, fever, generalized tonic–clonic seizure, and altered mental status. She was hospitalized in another hospital for 5 days, and then she was admitted to our hospital, and on the fifth day of the clinical scene, she had an MRI of the brain, which showed diffuse edema on the left temporal lobe extending to the insula, showing high signal on DWI, but ADC map did not show any hypointensity that would be restricted diffusion; hence, there was increased diffusion compatible with the subacute phase (Fig. 1). In another patient with a history of encephalitis, there was increased signal at the bilateral cortex on FLAIR, but DWI was normal with little increased signal on ADC map (Fig. 2).
Therefore, no diffusion abnormality in this study’s patients may be because they were imaged in the subacute or chronic phase. The article by Park, A. et al. is interesting; however, it would be better to clarify the diffusion features and the underlying reasons in a larger study group with RSV-related encephalitis. Conflict of interest I declare that I have no conflict of interest.
References 1. Park A, Suh S, Son GR, et al (2013) Respiratory syncytial virus-related encephalitis: magnetic resonance imaging findings with diffusionweighted study. Neuroradiology online first 13 Nov 2. Osborn AG (2010) Diagnostic Imaging: brain, vol 8, 2nd edn. Amirsys, Canada, pp 42–45 3. Kiroğlu Y, Calli C, Yunten N et al (2006) Diffusion-weighted MR imaging of viral encephalitis. Neuroradiology 48(12):875–880 4. Teixeira J, Zimmerman RA, Haselgrove JC, Bilaniuk LT, Hunter JV (2001) Diffusion imaging in pediatric central nervous system infections. Neuroradiology 43(12):1031–1039