Masked by Aneurysmal Hemorrhage: Herpes Simplex Virus (HSV)-2 Encephalitis in a Patient With Subarachnoid and Intraparenchymal Hemorrhage.

Herpes simplex virus (HSV) encephalitis is a neurologic emergency associated with significant morbidity and mortality. While HSV type 1 is the most common cause in adults, HSV type 2 (HSV-2) is a rare etiology of encephalitis and may present atypically. Intracranial hemorrhage is an uncommon complication of HSV encephalitis and can obscure diagnosis, particularly in critically ill patients with competing neurologic pathologies. Here, we present the case of a 73-year-old female with unknown past medical history who was found unresponsive and admitted with acute subarachnoid and intraparenchymal hemorrhage secondary to a ruptured right internal carotid artery aneurysm. She underwent external ventricular drain placement and endovascular aneurysm coiling. During her neuro-intensive care unit course, she developed recurrent fevers and progressive encephalopathy despite neurosurgical intervention and broad-spectrum antimicrobial therapy. Cerebrospinal fluid obtained from the ventricular drain demonstrated pleocytosis with significant red blood cell contamination, and bacterial cultures remained negative. Polymerase chain reaction (PCR) testing of the cerebrospinal fluid ultimately returned positive for HSV-2. Antibacterial therapy was discontinued, and intravenous acyclovir was initiated. This case highlights the diagnostic challenges of HSV-2 encephalitis in the setting of intracranial hemorrhage, where overlapping clinical features may delay recognition and treatment. HSV-2 encephalitis has been associated with vascular complications, including cerebral vasculitis and hemorrhage, though such presentations remain rare. HSV encephalitis should remain on the differential diagnosis for patients with persistent fever and worsening encephalopathy, even in the presence of an alternative structural neurologic diagnosis. Early consideration of viral etiologies and timely cerebrospinal fluid PCR testing are critical to avoid delays in antiviral therapy and potentially improve outcomes.