Not as Simple(x) as it seems: the importance of radiological follow-up in HSV encephalitis

An 18-year-old male, with no significant past medical history, presented to hospital with a frontal headache, pyrexia, and generalised tonic-clonic seizures. Examination revealed no focal neurological deficit. He was commenced on intravenous acyclovir for suspected Herpes Simplex Encephalitis (HSE), prior to confirmation of Herpes Simplex Virus (HSV) from positive cerebrospinal fluid analysis.

An initial computed tomography (CT) head revealed no acute intracranial pathology. A Magnetic Resonance (MRI) head with contrast advised by the neurology team detected diffuse hyperintense signals on T2W and FLAIR sequences within the right temporal lobe deep structures and insular cortex, suggestive of viral encephalitis.  

 Following completion of treatment, a repeat MRI head was performed due to persistent headache. It revealed new focal intraparenchymal haemorrhage within the right temporal lobe, with significantly more vasogenic oedema surrounding the evolving focal areas. In light of the intraparenchymal bleed with mass effect, urgent neurosurgical review was advised. A CT intracranial angiogram following the MRI to detect any active bleeding, demonstrated mild focal short segment stenosis of the mid-M1 segment of the right middle cerebral artery. The report suggests that the stenosis could be due to mass effect of the haemorrhage or inflammatory vasculopathy.

Background 

Intracranial haemorrhage is a complication affecting 2.7% of HSE patients, with a mortality rate of 21% [1]. One cause is small vessel vasculitis resulting in endothelial damage and secondary bleeding. Other suggested aetiologies include rupture and hypertension due to increased intracranial pressure, or an inflammatory reaction leading to brain tissue damage increasing vulnerability to bleeding [2]. The aim of the following case is to highlight this potentially fatal complication to avoid late diagnosis, ensuring early neurosurgical opinion is sought.  

Clinical Perspective 

HSE is the commonest fatal sporadic encephalitis in humans [3,4], with numerous clinical presentations including fever, decreased level of consciousness, seizures and behavioural disturbances. A delay in treatment with antivirals may result in permanent neuropsychological impairment, and increased mortality [5]. 

Imaging Perspective 

HSE often manifests as acute necrotising encephalitis, localising to the orbitofrontal and temporal lobes with involvement of the cingulate and insular cortex in most cases [3]. CT often shows a normal scan especially earlier on, however, later may reveal low densities in both the medial and anterior temporal lobes and the insular cortex [6]. MRI often shows corresponding T2W /FLAIR hyperintense signals in the frontal and temporal lobes [7].   

This case highlights the pivotal role of MRI, due to increased sensitivity compared to CT, identifying abnormalities early in the disease course of HSE. Although one study reported frequency-selective non-linear blending enhancement of CT being almost as good as T2W and FLAIR sequence MRI in identifying HSE [7], maximal enhancement is not possible to achieve in all settings. There are benefits and drawbacks to both imaging modalities. The possible cancer risk posed by CT is a downfall. However, MRI scans are often less readily available than CT and require more time to complete [6,8]. In addition to recognising radiological features of HSV encephalitis, a comprehensive and multidisciplinary approach looking at imaging in combination with clinical presentation and microbiology is essential for diagnosis [9]. 

Outcome 

Following antiviral treatment, the patient made a good recovery. He was followed up by the neurology team, reporting no further seizures, headaches or confusion whilst on the antiepileptic medication levetiracetam. A follow-up MRI head is scheduled for 10 months post-discharge to evaluate evolution of disease. 

Take-Home Message/Teaching Points 

• MRI is the preferred neuroimaging modality in HSE due to greater sensitivity. 
• Close monitoring and radiological follow up of HSE patients is imperative, even when antiviral treatment has been initiated promptly to monitor the disease progression. 
• Intracranial haemorrhage is a potential and rare serious complication of HSE manifests as necrotising infiltrates and scattered foci of small haemorrhage occasionally on MRI. Early identification is of paramount importance for appropriate management.