Abstract Details

Title The Great Imitator in the Dura: A Radiologic Transformation of West Nile Encephalitis

Topic General Neurology

Presentation(s) P5 - Poster Session 5 (11:45 AM-12:45 PM)

Poster/Presentation
Number 7-006

Objective To report an unusual case of West Nile meningoencephalitis presenting with isolated pachymeningeal enhancement that evolved into diffuse leptomeningeal involvement, expanding the recognized imaging spectrum of West Nile neuroinvasion.

Background Neuroinvasive West Nile virus (WNV) infection classically manifests with leptomeningeal or parenchymal inflammation, most often involving the basal ganglia, thalami, or brainstem. Isolated pachymeningeal enhancement and subdural effusions are distinctly uncommon and rarely described. Recognizing this divergent imaging pattern is critical to prevent diagnostic delay and unnecessary investigation for mimicking entities such as autoimmune pachymeningitis or intracranial hypotension.

Design/Methods

N/A

Results

A 71-year-old man with no significant medical history was found unresponsive in his hotel room; two days earlier he had been at neurologic baseline. On admission, he was obtunded and non-verbal, without focal deficits or trauma. Initial MRI with gadolinium revealed asymmetric pachymeningeal enhancement (left > right) without leptomeningeal involvement or parenchymal lesions. CSF analysis showed lymphocytic pleocytosis (52 WBC/µL).

Repeat MRI two days later demonstrated diffuse pachymeningeal enhancement with new bilateral subdural effusions and mild downward brainstem crowding. Despite these changes, the patient’s mental status remained unchanged. A third MRI several days later revealed resolution of the subdural effusions but new diffuse leptomeningeal enhancement bilaterally, marking a striking compartmental shift. Differential diagnoses at that stage included IgG4-related disease, autoimmune encephalitis, and viral meningoencephalitis. Repeat CSF showed 22 WBC/µL. Serum WNV IgM returned positive, confirmed by CSF IgM, establishing the diagnosis of West Nile meningoencephalitis.

Conclusions This case broadens the radiologic spectrum of West Nile neuroinvasive disease, demonstrating an evolving trajectory from pachymeningeal to leptomeningeal enhancement with transient subdural effusions. The dural-predominant phase may represent an underrecognized inflammatory interface in viral meningoencephalitis. Clinicians should maintain suspicion for WNV even when imaging is atypical and prioritize serologic testing despite negative molecular assays.

Authors/Disclosures
Kishan Patel, MD (University of Arizona Neurology) PRESENTER	Dr. Patel has nothing to disclose.
Amanpreet Sidhu, DO	Dr. Sidhu has nothing to disclose.
Geethika Ameneni, MD	Ms. Ameneni has nothing to disclose.
Sagi Elhassan, MD	Dr. Elhassan has nothing to disclose.

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