We present a rare case of encephalitis / ventriculitis with involvement of the fornix and cavum septum pellucidum secondary to VZV CNS infection.

Varicella Zoster Virus (VZV) is a leading cause of viral encephalitis. Most cases have normal neuroimaging and the most common abnormality found is large or small vessel CNS vasculopathy. The cavum septum pellucidum (CSP) is a normal variant CSF space. Infection involving the CSP is very rare.

Case Description:

A 60-year-old male presented with a 5-day history of behavioural change, diplopia and general malaise. Past medical history included T2DM and hyperlipidaemia.

On examination his GCS was 14 and he was afebrile. Cranial nerve examination revealed a left 6^th nerve palsy. Upper and lower limb neurological examination was normal. No rash was noted.  

Investigations:

Initial investigations revealed a CRP of 304 and CT brain showed a hypoattenuating cystic lesion between the lateral ventricles. MRI brain showed abnormal T2 FLAIR hyperintensity involving the anterior fornix and body of the fornix bilaterally with high signal extending along the margins of the septum pellucidum, with a cavum septum pellucidum and expansion of the cavum when compared to previous neuroimaging. CSF revealed positive VZV PCR and the patient was successfully treated with Acyclovir.

VZV is a common cause of infectious encephalitis. Encephalitis is reported to occur in ~0.25% of zoster cases. There is a wide range of radiological features associated with VZV encephalitis, however most cases have normal radiology. The most common abnormality described is a vasculopathy, with ventriculitis rarely described. Infection involving the CSP has rarely been reported.

Clinicians should maintain a high degree of clinical suspicion of VZV encephalitis regardless of immune status or evidence of cutaneous involvement. Further research is needed to characterise the imaging findings in VZV encephalitis.