title: MR imaging of adult acute infectious encephalitis.
abstract: BACKGROUND
  Imaging is a key tool for the diagnosis of acute encephalitis. Brain CT scan must be urgently performed to rule out a brain lesion with mass effect that would contraindicate lumbar puncture. Brain MRI is less accessible than CT scan, but can provide crucial information with patients presenting with acute encephalitis.
  
  
  METHODS
  We performed a literature review on PubMed on April 1, 2015 with the search terms "MRI" and "encephalitis".
  
  
  RESULTS
  We first described the various brain MRI abnormalities associated with each pathogen of acute encephalitis (HSV, VZV, other viral agents targeting immunocompromised patients or travelers; tuberculosis, listeriosis, other less frequent bacterial agents). Then, we identified specific patterns of brain MRI abnomalies that may suggest a particular pathogen. Limbic encephalitis is highly suggestive of HSV; it also occurs less frequently in encephalitis due to HHV6, syphillis, Whipple's disease and HIV primary infection. Rhombencephalitis is suggestive of tuberculosis and listeriosis. Acute ischemic lesions can occur in patients presenting with severe bacterial encephalitis, tuberculosis, VZV encephalitis, syphilis, and fungal infections.
  
  
  CONCLUSIONS
  Brain MRI plays a crucial role in the diagnosis of acute encephalitis. It detects brain signal changes that reinforce the clinical suspicion of encephalitis, especially when the causative agent is not identified by lumbar puncture; it can suggest a particular pathogen based on the pattern of brain abnormalities and it rules out important differential diagnosis (vascular, tumoral or inflammatory causes).
authors.affiliation: Service de neuroradiologie diagnostique et fonctionnelle, groupe hospitalier Pitié-Salpêtrière, 47-83 boulevard de l'hôpital, 75651 Paris cedex 13, France; Sorbonne universités, UPMC université Paris 06, Inserm, CNRS, institut du cerveau et la moelle (ICM), Inria Paris, Aramis project-team, 75013 Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Bertrand
authors.affiliation: Service de neuroradiologie diagnostique et fonctionnelle, groupe hospitalier Pitié-Salpêtrière, 47-83 boulevard de l'hôpital, 75651 Paris cedex 13, France.
authors.forename: D
authors.initials: D
authors.lastname: Leclercq
authors.affiliation: Service de neurochirurgie, CHU Nord, AP-HM, 13015 Marseille, France.
authors.forename: L
authors.initials: L
authors.lastname: Martinez-Almoyna
authors.affiliation: Service de neuroradiologie, CHU La-Timone, AP-HM, 13015 Marseille, France.
authors.forename: N
authors.initials: N
authors.lastname: Girard
authors.affiliation: Service d'infectiologie, CHU de Grenoble, « European study Group for the Infections of the Brain (ESGIB) », 38043 Grenoble, France. Electronic address: JPStahl@chu-grenoble.fr.
authors.forename: J-P
authors.initials: JP
authors.lastname: Stahl
authors.affiliation: Service de neurologie, CH Saint-Denis, BP 279, 93205, France.
authors.forename: T
authors.initials: T
authors.lastname: De-Broucker
mesh_terms: D000328:Adult; D003937:Diagnosis, Differential; D006801:Humans; D000069544:Infectious Encephalitis / Q000000981:diagnostic imaging* / Q000382:microbiology / Q000821:virology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D059906:Neuroimaging / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: Encephalitis; Encéphalite; HSV; IRM; Infection; MRI; VZV