Complicated viral encephalitis in a 16-year-old patient

16-year-old female who started with worsening headaches and fever, with additional behavioural and language impairment 4 days after. She then had a non-contrast head CT and an MRI performed and was admitted into ICU. 4 days later she developed consciousness deterioration and seizures, needing another head CT scan.

On the first non-contrast CT scan a subtle right temporal lobe hypodensity can be seen, which is better depicted in the following MRI. Predominantly right hemisphere bitemporal medial hyperintense areas can be seen either in the FLAIR and T2 sequences, apart from a semiologically identical lesion in the right insula.

The second CT scan (4 days later) shows bilateral sylvian hyperdense hemorrhagic foci corresponding to bilateral temporal hemorrhagic transformation with subarachnoid extension. Marked bilateral temporal hypodensity and swelling can be observed too, related to parenchymatous oedema and depicting descending transtentorial herniation signs.

CT angiography was carried out after intravenous contrast administration where right sylvian periarterial contrast material can be seen surrounding the right MCA, corresponding to the engorged right middle cerebral vein (which, in this case, drained into the sfenoparietal sinus -superficial venous circulation- instead of the Rosenthal vein -deep venous circulation-).

Herpes simplex encephalitis is the most common cause of fatal sporadic fulminant necrotizing encephalitis, typically caused by Herpes Simplex Virus 1 (HSV-1). The typical symptoms include fever, headaches, neurological focal symptoms, seizures and altered consciousness [1,2].

Imaging requests are frequent in order to dismiss cerebral abscess and depict signs of elevated intracranial pressure before lumbar puncture. Among typical CT scan findings, we can see subtle uni or bilateral (typically bilateral and asymmetric) medial temporal lobe and insular hypodensity, although a normal scan does not exclude the diagnosis. Faint patchy contrast enhancement may be depicted, typically after 7-10 days after disease onset [2,4,5].

MRI findings are similar to those described for the CT scan, T2 hyperintensity in the affected areas being the most salient finding. ADC maps and DWI sequences have a higher sensitivity, showing mild to moderate restriction diffusion due to cytotoxic oedema. T1 hyperintense areas might be observed if hemorrhagic complications appear. Gadolinium enhancement is a late finding in the disease and can be seen as gyral, leptomeningeal or diffuse enhancement [2,3,5].

In this particular case, the patient’s symptoms and the typical distribution of the findings, particularly after MRI imaging, suggested viral herpes encephalitis as the most plausible diagnosis.

Definitive diagnosis can be achieved if a cerebrospinal fluid (CSF) Polymerase Chain Reaction (PCR) test is positive for HSV-1, but elevated protein and pleocytosis in the CSF associated to a highly suggestive clinical scenario might be enough for treatment start (intravenous acyclovir) [1,2].

CSF was obtained in our patient, showing marked lymphocytosis, elevated proteins and a Herpesvirus positive PCR, confirming herpes simplex encephalitis diagnosis. She then started treatment with intravenous acyclovir and corticosteroids.

Disease prognosis depends on time from symptom start and treatment onset and the development of complications. Overall mortality in previously healthy patients who do not suffer from any complications is about 20%, being up to 75% in comatose patients who suffer any kind of complications. It is estimated that less than 5% of the patients fully recover their neurological functions after healing [1,2,6].

Typical complications of herpes simplex encephalitis are cytotoxic oedema (which may cause cerebral herniation) and seizures, features that can be seen in our patient. Furthermore, intraparenchimatous hemorrhagic transformation is a rare complication of herpetic encephalitis, dramatically impairing patient survival. Proposed theories suggest it happens either due to endothelial damage secondary to small-vessel vasculitis or due to increased intracranial pressure [6].

Our patient underwent right temporal decompressive craniectomy, with positive neurological and radiological outcomes.