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Difficulty: Very hardInterpreting Imaging Results

A 45-year-old woman is brought to the emergency department by her husband due to a severe headache, confusion, and a witnessed generalized tonic-clonic seizure. She has a history of poorly controlled hypertension and medication non-adherence. On arrival, her blood pressure is 225/125 mm Hg, heart rate is 105/min, and respiratory rate is 18/min. She is postictal and somnolent.

After initial airway protection, an expedited MRI of the brain is performed due to the institution's stroke protocol. The MRI demonstrates the following specific findings:
- T2-weighted and fluid-attenuated inversion recovery (FLAIR) sequences show symmetric, bilateral, confluent areas of hyperintensity in the subcortical white matter of the parietal and occipital lobes.
- Diffusion-weighted imaging (DWI) shows iso-intensity to mild hyperintensity in the corresponding regions.
- Apparent diffusion coefficient (ADC) mapping reveals marked hyperintensity in these same parieto-occipital areas.

Based on the interpretation of these imaging results, which of the following is the most appropriate next step in management?

  1. Continuous intravenous infusion of nicardipineAnswer
  2. B
    Intravenous administration of alteplase
  3. C
    Conventional digital subtraction angiography
  4. D
    Intravenous administration of high-dose methylprednisolone
  5. E
    Lumbar puncture with cerebrospinal fluid analysis

Answer

Continuous intravenous infusion of nicardipine
The patient's clinical presentation of a hypertensive emergency (blood pressure 225/125 mm Hg), accompanied by headache, encephalopathy, and seizures, combined with the classic MRI findings, is pathognomonic for Posterior Reversible Encephalopathy Syndrome (PRES). The key to this question is interpreting the MRI sequences correctly. Extreme hypertension exceeds the upper limit of cerebral autoregulation, leading to endothelial dysfunction and the transudation of fluid into the brain interstitium. This creates vasogenic edema. On MRI, vasogenic edema demonstrates increased or facilitated diffusion, which appears as marked hyperintensity on an Apparent Diffusion Coefficient (ADC) map. In contrast, an acute ischemic stroke causes failure of the Na+/K+ ATPase pump, leading to cellular swelling and true restricted diffusion (cytotoxic edema). Cytotoxic edema classically appears bright on Diffusion-Weighted Imaging (DWI) and strictly dark (hypointense) on the ADC map. Because the patient's ADC map shows marked hyperintensity, acute infarction is ruled out. The cornerstone of PRES management is the immediate but controlled reduction of blood pressure using an easily titratable intravenous antihypertensive agent, such as a continuous infusion of nicardipine, clevidipine, or labetalol.

Step-by-Step Solution

1
Analyze the clinical presentation
The patient has a hypertensive emergency (blood pressure 225/125 mm Hg) complicated by severe neurological symptoms including headache, encephalopathy, and a seizure.
To establish the acute clinical syndrome and recognize the need for immediate intervention.
2
Interpret the specific MRI sequences
The MRI shows parieto-occipital white matter lesions that are hyperintense on FLAIR and markedly hyperintense on the ADC map.
To differentiate the underlying pathophysiology of the cerebral edema.
3
Correlate imaging physics with the diagnosis
The hyperintense ADC signal confirms increased (facilitated) diffusion, indicating vasogenic edema. This distinguishes it from the restricted diffusion (hypointense ADC signal) of cytotoxic edema seen in acute ischemic stroke.
To definitively diagnose Posterior Reversible Encephalopathy Syndrome (PRES) and rule out acute infarction.
4
Determine the most appropriate management
The primary treatment for PRES is the prompt, controlled reduction of blood pressure using a titratable intravenous agent.
To reverse the endothelial dysfunction and prevent irreversible neurological damage.

Key Concept

Posterior Reversible Encephalopathy Syndrome (PRES) is characterized on MRI by vasogenic edema, which appears hyperintense on Apparent Diffusion Coefficient (ADC) mapping. This distinguishes it from acute ischemic stroke, which presents with cytotoxic edema and restricted diffusion (hypointensity) on ADC mapping.
Estimated Time:2m 0s
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Interpreting Imaging Results

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