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Difficulty: Very hardOrdering Imaging Studies

A 32-year-old woman, G2P1, at 18 weeks gestation is brought to the emergency department by emergency medical services. Her husband reports that she suddenly lost the ability to speak and developed severe weakness on her right side approximately 45 minutes ago. Upon arrival, her blood pressure is 145/88 mmHg, heart rate is 92/min, and respiratory rate is 16/min. Neurological examination reveals a dense right-sided hemiplegia, right lower facial droop, and global aphasia. Her National Institutes of Health Stroke Scale (NIHSS) score is 18. The patient is otherwise healthy, and her pregnancy has been uncomplicated. Suspecting an acute ischemic stroke with a possible large vessel occlusion (LVO), the clinical team prepares for immediate neuroimaging to determine her candidacy for reperfusion therapy.

Which of the following is the most appropriate initial sequence of imaging studies for this patient?

  1. Non-contrast computed tomography (CT) of the head and CT angiography (CTA) of the head and neckAnswer
  2. B
    Magnetic resonance imaging (MRI) of the brain and MR angiography (MRA) of the head and neck without gadolinium
  3. C
    Magnetic resonance imaging (MRI) of the brain and MR angiography (MRA) of the head and neck with gadolinium
  4. D
    Non-contrast computed tomography (CT) of the head followed by magnetic resonance angiography (MRA) of the head and neck without gadolinium
  5. E
    Digital subtraction angiography (DSA) of the brain

Answer

Non-contrast computed tomography (CT) of the head and CT angiography (CTA) of the head and neck
The correct sequence for evaluating a hyperacute stroke to determine candidacy for mechanical thrombectomy is a non-contrast CT of the head (to quickly rule out intracranial hemorrhage) followed immediately by a CT angiography (CTA) of the head and neck (to identify a large vessel occlusion). Pregnancy is a common source of cognitive bias leading to inappropriate delays in imaging due to fear of radiation. However, the fetal radiation dose from a maternal head and neck CT/CTA is extremely low (less than 0.01 mGy) and far below the threshold for fetal harm (typically >50 mGy). Iodinated contrast does cross the placenta, but it is not teratogenic and its use is justified in life-threatening emergencies. The maternal benefit of rapid diagnosis and reperfusion far outweighs any theoretical fetal risk.

Step-by-Step Solution

1
Identify the clinical syndrome and its acuity.
The patient presents with acute right hemiplegia and global aphasia starting 45 minutes ago, placing her in the hyperacute window for stroke interventions.
This establishes that time is the most critical factor, dictating that the fastest possible imaging modalities must be chosen.
2
Assess the patient's specific physiological state.
The patient is pregnant at 18 weeks gestation.
Pregnancy introduces concerns regarding fetal radiation exposure and contrast safety, which often leads to cognitive bias and inappropriate test selection.
3
Evaluate the safety profile of the required imaging.
Fetal radiation exposure from maternal head and neck CT/CTA is negligible (<0.01 mGy). Iodinated contrast crosses the placenta but is considered safe in life-threatening emergencies.
This confirms that the standard of care for acute stroke is not contraindicated by pregnancy.
4
Select the optimal imaging sequence.
Non-contrast CT of the head to rule out hemorrhage, followed immediately by CTA of the head and neck to evaluate for LVO.
This sequence provides the necessary information for mechanical thrombectomy planning with the least delay, maximizing the chance of preserving maternal neurological function.

Key Concept

In pregnant patients presenting with acute ischemic stroke, the standard rapid neuroimaging protocol (non-contrast CT followed by CTA) should not be delayed or altered, as fetal radiation risk from head and neck imaging is negligible and the maternal benefit is life-saving.
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Ordering Imaging Studies

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