A 58 year old man presented to an outside hospital with fever, diarrhea, and depressed mental status. Upon transfer to our institution three days later, he was noted to have severe encephalopathy, with eyes open but no regarding or command following. His neurologic examination was notable for bilateral hippus, roving eye movements with spontaneous direction-changing nystagmus, eyelid myoclonus, and severe bifacial weakness. His tone was markedly increased in axial musculature and lower extremities with paratonia and cogwheeling in upper extremities. Magnetic resonance imaging (MRI) of the brain revealed sulcal effacement of the superior frontal lobes at the vertex with associated T2/FLAIR hyperintensity along with layering restricted diffusion in the dependent portions of bilateral occipital horns. Cerebrospinal fluid (CSF) analysis revealed a white blood cell count of 20/uL with lymphocytic predominance and protein of 105 mg/dL. CSF West Nile Virus (WNV) IgM resulted positive with negative IgG. Ophthalmologic exam revealed evidence of WNV retinitis. The patient’s neurologic exam subsequently improved, able to follow simple commands and nod to questions appropriately with resolution of hypertonia but persistence of saccadic impairments and bifacial weakness. The patient required tracheostomy and percutaneous gastrostomy tube and was discharged to a long term acute care facility to allow for continued recovery. Repeat MRI brain at four weeks revealed interval development of subcortical and periventricular T2/FLAIR hyperintensities as well as mild hydrocephalus and interval resolution of previous intraventricular findings.

This case reveals an unusual MRI finding of dependent ventricular restricted diffusion suggestive of pyogenic ventriculitis in a patient with WNV encephalitis. This has not previously been reported in the literature. Neuroinvasive flaviviruses, such as WNV, are capable of crossing the blood-brain barrier and entering the brain parenchyma. Extensive viremia with WNV may cause subependymal involvement and may have led to intraventricular involvement in this case.