Cortical melt sign: a novel imaging biomarker for pediatric herpes simplex encephalitis

Herpes simplex virus 1 encephalitis (HSE) is the most common sporadic infectious encephalitis in Western countries, with a 70% mortality rate and only 9% of survivors free from neurological sequelae. While definitive diagnosis relies on cerebrospinal fluid testing, magnetic resonance imaging (MRI) plays a crucial role in identifying typical acute patterns and features. However, the imaging evolution of encephalitic lesions is not well understood. We aimed to identify and evaluate the prevalence and progression of cortical lesions, as well as the recurrence of these patterns in HSE and other encephalitic etiologies.

As a retrospective monocentric study, we included 40 patients with various etiological encephalitis from our institute. Each patient's lesions were assessed, by three experienced neuroradiologists, in the acute phase and associated with specific evolution patterns in the chronic phase.

10 out of 11 (91%) patients diagnosed with HSV-1 presented during chronic phase selective cortical liquefaction, identified as Cortical Melt Sign (CMS) (Fisher's exact p-value < 0.001). Moreover, this pattern was then correlated with acute diffusion restriction-potentially explaining CMS as a chronic imaging biomarker for HSE as a result of the acute inflammation.

These findings can aid in understanding the pathological mechanisms of herpetic encephalitis and guide differential diagnosis. Moreover, CMS could serve as a retrospective imaging marker in HSE.