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. 2016 Oct;71(10):1050-8.
doi: 10.1016/j.crad.2016.03.015. Epub 2016 May 13.

Neuroimaging in encephalitis: analysis of imaging findings and interobserver agreement

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Free PMC article

Neuroimaging in encephalitis: analysis of imaging findings and interobserver agreement

J Granerod et al. Clin Radiol. 2016 Oct.
Free PMC article


Aim: To assess the role of imaging in the early management of encephalitis and the agreement on findings in a well-defined cohort of suspected encephalitis cases enrolled in the Prospective Aetiological Study of Encephalitis conducted by the Health Protection Agency (now incorporated into Public Health England).

Materials and methods: Eighty-five CT examinations from 68 patients and 101 MRI examinations from 80 patients with suspected encephalitis were independently rated by three neuroradiologists blinded to patient and clinical details. The level of agreement on the interpretation of images was measured using the kappa statistic. The sensitivity, specificity, and negative and positive predictive values of CT and MRI for herpes simplex virus (HSV) encephalitis and acute disseminated encephalomyelitis (ADEM) were estimated.

Results: The kappa value for interobserver agreement on rating the scans as normal or abnormal was good (0.65) for CT and moderate (0.59) for MRI. Agreement for HSV encephalitis was very good for CT (0.87) and MRI (0.82), but only fair for ADEM (0.32 CT; 0.31 MRI). Similarly, the overall sensitivity of imaging for HSV encephalitis was ∼80% for both CT and MRI, whereas for ADEM it was 0% for CT and 20% for MRI. MRI specificity for HSV encephalitis between 3-10 days after symptom onset was 100%.

Conclusion: There is a subjective component to scan interpretation that can have important implications for the clinical management of encephalitis cases. Neuroradiologists were good at diagnosing HSV encephalitis; however, agreement was worse for ADEM and other alternative aetiologies. Findings highlight the importance of a comprehensive and multidisciplinary approach to diagnosing the cause of encephalitis that takes into account individual clinical, microbiological, and radiological features of each patient.


Figure 1
Figure 1
Cases where there was consensus agreement of ADEM diagnosis when reviewing neuroimaging. A 5-year-old male patient (Case 1b26023) with a 5-day history of pyrexia, increasing lethargy, and mild cough/cold; on presentation he had left-sided weakness, ptosis, and unequal pupils noted. (a–c) Axial T2 and (d–f) FLAIR images demonstrating hyperintensity within medial thalamus (arrows; a, d), left cerebral peduncle (arrow; b, c) and left dentate nucleus (not shown) extending in to cerebellar pontine angle (arrow; c, f); with some more widespread white matter lesions as seen on axial flair images in centrum semiovale (g). (h–i) A 5-year-old female patient (Case 1b26029) with a history of lethargy, leg weakness, and unsteadiness walking; also had recent episodes of urinary incontinence. (h) Axial T2 imaging demonstrating bilateral basal ganglia and thalamic lesions and (i) widespread deep and subcortical white matter lesions.
Figure 2
Figure 2
Cases where there was no consensus agreement of ADEM diagnosis when reviewing neuroimaging. A 2-year-old female patient (Case 1b26010) with a 2-day history of unsteadiness; on assessment noted to be ataxic with intention tremor and reluctance to weight bear. (a,b) Axial T2 and (c,d) FLAIR images demonstrating periventricular hyperintensity, which might have been interpreted as terminal zones of myelination (a,c). A solitary, high signal lesion within the cerebellar white matter was seen (arrow; b,d). (e–f) A 40-year-old woman (Case 1c31011) presented with fever, cough, diplopia, dysarthria, and paraesthesia in the feet ascending to the trunk. (e,f) Axial T2 and flair (not shown) images demonstrating symmetrical high signal lesions within the basal ganglia and thalamus (e) cerebral peduncle and periaqueductal grey matter (f). Here, the homogeneous and symmetrical lesion would have prompted the consideration of a neurometabolic disorder, such as a mitochondrial cytopathy, when reviewing the images.
Figure 3
Figure 3
Sensitivity, specificity, NPV, and PPV of CT (a) and MRI (b) for HSV by timing of the scan from symptom onset. PPV in 0–2 day category could not be calculated due to zero patients in this timing category with a CT that looks like HSV (i.e. zero denominator).

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