The patient went on to have a craniotomy and biopsy.
These are fragments of cerebral cortex and white matter showing extensive areas of parenchymal necrosis, with sheets of foamy macrophages and degenerating neutrophils. Within areas of incipient necrosis there are numerous red neurons, some of which show intraneuronal inclusions. The adjacent parenchyma shows marked reactive astrocytosis and microglial activation, with occasional microglial nodules. There is a necrotising small vessel vasculitis, with occasional vessels showing luminal microthrombi and perivascular haemorrhage. There is dense infiltration around and within the walls of parenchymal and leptomeningeal vessels by a mixed inflammatory infiltrate, including lymphocytes (with some activated forms) and plasma cells.
Immunohistochemistry for HSV-1/2 shows positive staining in some neurons and occasional glial cells; this confirms a diagnosis of herpes encephalitis.
DIAGNOSIS: Right temporal lobe specimens, including medial structures and uncus: extensively necrotising herpes simplex encephalitis.