Herpes simplex encephalitis

Case contributed by Shimalis Tadasa Fayisa
Diagnosis certain


Five days of headaches and altered behavior.

Patient Data

Age: 50 years
Gender: Male

brain CT with contrast


Right temporal lobe medial and anterior portions, as well as the right insular cortex, have low density and loss of gray-white matter distinction. The left mesial temporal lobe and both paramedian lower frontal lobes similarly exhibit a subtle low density.

Hemorrhagic changes and contrast enhancement were not visible.

01 weeks later


Right temporal lobe exhibits high T2/FLAIR and low T1 signal intensity, extending to the right insular cortex, hippocampal, parahippocampal gyrus, and anteroinferior right occipital lobe with swollen gyrus, effacement of surrounding sulci and right occipital horn of lateral ventricle.

Additionally, the left mesial temporal lobe and insular cortex showed high T2/FLAIR and low T1 signal intensities, along with involvement of the bilateral lower paramedian frontal lobes.

Restricted diffusion is more subtle than infarction in the areas of the brain where the signal intensity changes.

Neither hemorrhagic nor enhanced lesions were visible.

The bilateral basal ganglia remain unaffected.

There is no evidence of hydrocephalus.

Bilateral maxillary sinus mucosal high T2, low T1 with no enhancement detected suggesting its fluid—common accidental observations.


Herpes simplex encephalitis is suspected based on the patient's history of headaches and behavioral changes lasting five days, as well as imaging results showing bilaterally asymmetric involvement of the medial temporal lobe, insular cortices, and infero-medial frontal lobe.

Case Discussion

The patient was scanned with a CT scan (there was no MRI machine on site) and had a lumbar puncture after arriving at the emergency room. CSF analysis ,showed leukocytosis with 100% lymphocytes, elevated protein, normal glucose levels, negative gram stain, and viral PCR result revealing HSV-1.
The patient was admitted to the hospital and intravenous antiviral (Acyclovir) was started.

After a week had passed with no clinical improvement, an MRI was performed at a nearby facility. There were no additional complications found, and the same care continued with the previous working diagnosis. The patient recovered and was discharged after completing the antiviral course.

The leading non-epidemic and sporadic cause of viral fulminant encephalitis is the herpes simplex virus. Changes are typically detectable within 2-3 days of the onset of symptoms, making MRI the most sensitive radiological investigation. A typical MRI finding of herpes simplex encephalitis shows bilateral asymmetrical limbic system involvement, covering medial temporal lobes, insular cortices, infero-lateral frontal lobes, and cingulate gyri. Basal ganglia are usually spared.

Herpes simplex encephalitis is typically fatal in elderly patients, hence early diagnosis and the use of antivirals are crucial to a patient's prognosis.

Differential diagnoses like gliomatosis cerebri and infarcts in the MCA territory are taken into consideration.

However, observing preserved basal ganglia, a non-territorial pattern of damage, a clinical finding of a brief headache, and a behavioral shift aids in ruling out.

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