Structured Imaging Approach for Viral Encephalitis

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Key points

  • Understanding the typical MR imaging (MRI) patterns caused by archetype viral pathogens is important, despite considerable overlap, diagnostic uncertainty, and unknown etiologies among patients with acute encephalitis syndrome.

  • Acute encephalitis caused by herpes simplex virus type 1 typically affects the temporal lobe.

  • In patients with bi-thalamic involvement, Japanese encephalitis and influenza-associated encephalitis should be considered.

  • Enterovirus and rabies virus infections can involve the

Structured approach to image analysis

MR imaging has demonstrated its value in assessing viral encephalitis.11 This article proposes a structured diagnostic approach using MR imaging-based neuroanatomical localization and pattern recognition (Fig. 1). First, the course of the disease should be determined: if it is acute (ie, AES) or chronic (ie, CE). The next step involves the assessment of MR imaging abnormalities based on the anatomic location. It forms a framework to understand viruses that preferentially show MR imaging changes

Herpes simplex virus type-1

The annual incidence of HSV encephalitis (HSE) has been estimated to be ∼2 to 4 individuals/million population worldwide.12 More than 90% of HSE results from HSV type-1 (HSV-1) infection in adults, while HSV-2 infection usually occurs in neonates or immunocompromised patients.13 In addition, about 30% of HSE cases occur from a primary HSV-1 infection, whereas the remaining cases are attributed to viral reactivation or reinfection.14 The incidence of HSE from HSV-1 infection has a bimodal age

Subacute or chronic course

Viruses can rarely present with a subacute or chronic course, particularly human immunodeficiency virus (HIV) and associated complications. Readers are encouraged to refer to article 9 for neuroimaging features of HIV.

Summary

Clinical diagnosis of the cause of viral encephalitis can be difficult. Nonetheless, an accurate and timely diagnosis is essential to guide management and appropriate treatment. In this article, a diagnostic algorithm based on MR imaging features is proposed to systematically aid the differential diagnosis of viral encephalitis. The typical MR imaging patterns should not be overlooked (Table 2).

The proposed MR imaging findings must be interpreted in the correct clinical context, and thus,

Clinics care points

  • Viruses can cause central nervous system disease via three broad mechanisms: aseptic meningitis, encephalitis, and immune-mediated processes; adopting a structured but simplified diagnostic approach based on typical MR imaging patterns can assist in suggesting a viral pathogen, even though there is considerable overlap.

  • By aggregating imaging, clinical and laboratory evidence, radiologists can contribute to multidisciplinary teams caring for patients, leading to the appropriate treatment and

Disclosure

The authors have nothing to disclose.

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