Herpes simplex encephalitis: unusual imaging appearances

Autoimmune and infectious diseases.

“…Brain MRI is highly sensitive in detecting abnormalities in HSE, which most commonly include bilateral asymmetrical involvement of the limbic system, including the mesial temporal lobe, insular cortices, inferolateral frontal lobes, and cingulate gyri (Bulakbasi & Kocaoglu, 2008). Sparing of the basal ganglia is a key feature, which also helps in differentiating from middle cerebral artery infarction on diffusion-weighted imaging (DWI; Bonnici-Mallia et al, 2016). Despite acute clinical recovery posttreatment, many patients with HSE will continue to demonstrate mesial temporal lobe/limbic damage via MRI findings (Scheel & Finke, 2018), which is likely a key correlate to persistent cognitive impairment seen in memory and language, as well as personality and behavior changes (McGrath et al, 1997).…”

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“…Herpetic meningo encephalitis (HME) is a sporadic, nonepidemic acute disease with an incidence of approximately 1 to 3 cases per million [1,2]. 95% of fatal cases in adults are due to Herpes Simplex Virus type 1.…”

“…In neonatal period and children Herpes Simplex Virus type 2 is most often the culprit (80 to 90%). The virus reaches the nervous system via the respiratory tract and then the trigeminal ganglion where it becomes latent in non immunocompromise patients [1,3]. The reactivation of the virus would be secondary to a decrease immunity due to genetic mutation on neurons and oligidendrocytes altering interferon production which normally inhibits viral replication [3,4].…”

“…The reactivation of the virus would be secondary to a decrease immunity due to genetic mutation on neurons and oligidendrocytes altering interferon production which normally inhibits viral replication [3,4]. This situation probably explains the preferential involvement of internal temporal lobe (early in the course) because of the anatomical proximity with the meckel's cavum that houses the trigeminal ganglion (Figure 1) [1,5]. Extratemporal involvement only is also possible [2].…”

“…It typically shows bilateral, asymmetrical involvement of the brain predominantly in the limbic system (medial temporal lobe, insular cortex, cingular gyrus, infero-lateral frontal lobe), with or without extension to the basal ganglia and the other lobes (Figure 3). Diencephalon and brain stem involvement are possible [1] Bonnici-Malia reported a case of hypothalamic and optochiasmatic involvement. Extra temporal involvement only can also be observed.…”