Differential Diagnosis for Altered Mental Status with Parieto-Temporal Hyperdense Lesion on CT Brain

• Single Most Likely Diagnosis
  • A. Herpes Encephalitis: This is a common cause of encephalitis, particularly in young patients, and often presents with temporal lobe involvement, which can appear as hyperdense lesions on CT scans due to hemorrhage or necrosis.
• Other Likely Diagnoses
  • B. Meningoencephalitis: Inflammation of both the meninges and the brain parenchyma can cause altered mental status and may show hyperdense lesions on CT due to inflammation or edema.
  • C. Brain Abscess: Although the description mentions a "double rim sign," which is characteristic of brain abscesses, the presence of a hyperdense lesion could still suggest an abscess, especially if the patient has a history of infection or immunocompromised state.
• Do Not Miss Diagnoses
  • Subarachnoid Hemorrhage or Intracerebral Hemorrhage: Although not explicitly listed, any condition causing sudden altered mental status and hyperdense lesions on CT should prompt consideration of hemorrhagic strokes, which are medical emergencies.
  • Cerebral Venous Thrombosis: This condition can cause hyperdense lesions due to thrombosis and subsequent infarction, particularly in the parietal and temporal regions, and is critical to diagnose due to its high morbidity and mortality if untreated.
• Rare Diagnoses
  • D. Cerebral Hydatid Cyst: While this is a possible cause of a brain lesion, it is less common in most populations and typically presents with cystic lesions that may not initially appear hyperdense on CT unless they are infected or have ruptured.
  • Other rare infections or inflammatory conditions: Such as neurocysticercosis, toxoplasmosis (in immunocompromised patients), or autoimmune encephalitis, which can present with a variety of imaging findings including hyperdense lesions.