Chapter 16. Neuroradiology
A 50-year-old man with no significant past medical history and no contributory family history presented to the emergency room with a history of subacute personality changes that progressed into confusion over a period of 5 days. In the emergency department, he had a witnessed generalized tonic–clonic seizure. He was febrile (101°F). Cerebrospinal fluid analysis revealed RBCs 3,000/mm3, protein 50 mg/dL, WBC 45 cells/mm3, and normal glucose level. Magnetic resonance imaging (MRI) of the brain was obtained (Figure 16-1).
Figure 16-1 (Reproduced with permission from Block J, Jordanov MI, Stack LB, et al. The Atlas of Emergency Radiology. New York: McGraw-Hill Education, Inc; 2013.)
Which of the following is the most likely diagnosis?
(B) MRI findings are benign and likely related to the seizure activity
(C) Herpes simplex virus-1 (HSV-1) encephalitis
(D) West Nile encephalitis
(C) The most likely diagnosis is herpes simplex virus (HSV)-1 encephalitis. Approximately 2,000 cases of HSV-1 encephalitis are diagnosed every year in the United States. HSV encephalitis occurs sporadically throughout the year and in patients of all age groups. The majority of cases are caused by HSV-1, which is the cause of common herpetic lesions of the oral mucosa. HSV-2 may also cause acute generalized encephalitis, usually in the neonate and in association with a maternal genital herpetic infection. HSV-2 infection in the adult more typically causes aseptic meningitis, polyradiculitis, or myelitis, commonly in association with a recent genital herpes infection. Symptoms of HSV-1 encephalitis include fever, headache, seizures, confusion, stupor, and coma. CSF analysis commonly reveals increased opening pressure, pleocytosis (mostly lymphocytes; range of 10 to 200 cells/mm3; infrequently greater than 500 cells/mm3), and increased RBCs. Classic radiographic findings of HSV encephalitis are seen best with MRI demonstrating a T2/FLAIR hyperintensity in the medial temporal lobes, insular cortex, and inferior frontal lobes. The basal ganglia are typically spared, which can distinguish HSV encephalitis from an infarct in the middle cerebral artery territory in the majority of cases.
Intravenous acyclovir is the drug of choice in patients with acute HSV-1 encephalitis. Mortality and morbidity are governed to a large extent by the patient's age and state of consciousness, particularly at the time of institution of acyclovir therapy. (Ropper, 719–722; Block, 80–88)
Ropper AH, Samuels MA, Klein JP. Adams & Victor's Principles of Neurology. 9th ed. New York, NY: McGraw-Hill; 2014.
Block J, Jordanov MI, Stack LB, et al. The Atlas of Emergency Radiology. New York, NY: McGraw-Hill; 2013.