Diagnosis:
Herpes simplex encephalitis
• The clinical picture of herpes simplex encephalitis involves nonspecific features of encephalitis (headache, neck stiffness) and focal neurologic signs (e.g., dysphagia, hemiparesis, focal seizures). CSF examination may reveal a moderate leukocytosis and elevated protein levels.
• Acute presentation is characterized by bilateral, usually asymmetrical, congestion and hemorrhagic necrosis involving the temporal lobes. The lesions can extend from the pial surface through the cerebral cortex and into the white matter.
• A mild to moderate lymphocytic infiltrate is present in the leptomeninges and some is seen within the parenchyma. Affected cells (neurons, glia, and endothelial cells) have a slightly hypereosinophilic cytoplasm and the nuclei are pyknotic and can contain homogeneous eosinophilic inclusions. An irregular rim of condensed marginated chromatin can be seen.
• Cowdry type A inclusions, eosinophilic inclusions surrounded by a clear halo, and marginated chromation, can be present in infected cells, especially along the periphery of the lesion. Immunocytochemistry provides a sensitive assay for herpes.
• In long term survivors, affected parts of the brain are shrunken and cavitated. A glial scar replaces the normal gray and white matter and some inflammatory component may remain.
Ellison D, Love S, Chimelli L, et al (eds): Neuropathology: A Reference Text of CNS Pathology, 3rd ed. Edinburgh: Mosby Elsevier, 2013.
Love S, Louis DN, Ellison DW (eds): Greenfield’s Neuropathology, 8th ed. London: Hodder Arnold, 2008.
