Hyperdense vessel sign is defined as focal increased attenuation of a vessel (either artery or vein) seen on non-contrast Computed tomography (NCCT). This is due to vessel occlusion, mainly by a thrombus or embolus. The high attenuation of a thrombus is due to the extrusion of plasma in the thrombus with a subsequent increase in the local hematocrit level. It is most observed in the middle cerebral artery (MCA) in ischemic stroke. However, hyperdense signs can also be observed due to other causes which are deemed as false positive.

Here we report a 26-year-old male patient with no past medical history, presented to our emergency department with history of fever, headache, and confusion for 2 days. On the day of admission, he had 3 episodes of seizure and was therefore brought to the hospital. On assessment, the patient was conscious but not communicating. Physical examination showed neck stiffness, power is normal in all four limbs. NCCT brain showed subtle hypodensity involving the right parietotemporal region with hyperdense MCA. Subsequently, computed tomography (CT) angiography of the head was done and revealed normal blood vessels with a pseudo-hyperdense MCA sign on the right side. Lumbar puncture showed findings suggestive of viral encephalitis with positive herpes simplex virus (HSV) polymerase chain reaction (PCR).