A stroke, also known as a cerebrovascular accident (CVA), is a serious medical condition that occurs when the blood supply to part of the brain is interrupted or reduced, preventing brain tissue from getting oxygen and nutrients. This can be due to a blocked artery (ischemic stroke) or burst blood vessel (hemorrhagic stroke). Strokes require emergency medical treatment as they can cause permanent damage or even death if not addressed quickly.
Medical imaging tests like CT scans and MRI scans are commonly used to help diagnose strokes by allowing doctors to visualize the brain and identify areas of injury or bleeding. However, one of the big questions surrounding stroke diagnosis is whether it’s possible for a stroke to be “missed” on a scan, with no abnormalities detected even when a stroke has occurred.
What types of scans are used to diagnose stroke?
The two main types of scans used to diagnose stroke are:
– CT (computed tomography) scan: This test uses X-rays and a computer to create cross-sectional images of the brain. It can detect bleeding and larger areas of damage quickly. CT scans are often the first test ordered for suspected stroke.
– MRI (magnetic resonance imaging) scan: This test uses radio waves and strong magnets to generate more detailed images of the brain’s structure and tissues. It can detect smaller areas of injury that may be missed on a CT scan. MRI is more sensitive than CT overall.
Some key points about using scans for stroke:
– CT scans are widely available and can be performed quickly, so they are often used for initial assessment.
– MRI provides more comprehensive information but takes longer to perform and may not be available urgently.
– Sometimes both CT and MRI scans are used together to get a complete picture.
– Imaging tests like CT and MRI allow doctors to determine what type of stroke occurred (ischemic or hemorrhagic) and pinpoint the location of blockage or bleeding in the brain.
– Findings on the scans guide urgent treatment decisions.
Are strokes ever missed on scans?
Unfortunately, the short answer is yes – it is possible for acute strokes to be missed on imaging under certain circumstances. Here are some reasons why this can occur:
1. Scan performed too early
Changes within the brain tissue may not be substantial enough to appear on a scan done immediately after stroke symptoms start. Damage and abnormalities become more evident over hours as the area becomes infarcted (dead tissue). A follow-up scan done 6-12 hours later or the next day is more likely to detect the stroke.
2. Small size of stroke
Extremely small strokes confined to a limited area of the brain may not be picked up on an initial scan. Detailed MRI imaging has the best chance of identifying these small infarcts.
3. Location in the brain
Certain parts of the brain like the brainstem, cerebellum and occipital lobe have a very complex structure. Small strokes in these areas can be harder to recognize on scans compared to other locations.
4. Human error
Misinterpretation of scans by the radiologist or neurologist can lead to strokes being missed. Subtle early signs of infarction may not be noticed if the scans are not examined thoroughly. Fatigue, distractions and other factors can contribute to human error.
5. Patient factors
Medical conditions like severe hypoglycemia or seizures can cause neurological symptoms that mimic stroke. In such cases, scans may be normal if not an actual stroke. Elderly and diabetic patients are more prone to this issue.
6. Technical factors
Poor quality images due to motion artifacts or technical issues with the scanning device itself reduces the sensitivity for picking up strokes. Malfunctioning equipment should be identified and fixed to prevent misses.
How often are strokes missed on initial scans?
Several research studies have tried to determine the frequency of strokes being missed on the first scans:
| Study | Type of Scan | Stroke Miss Rate |
|---|---|---|
| Baxter et al. (2016) | CT scan | 13% |
| Gargalas et al. (2020) | CT scan | 10.8% |
| Leary et al. (2003) | MRI scan | 8.6% |
| Kumar et al. (2010) | CT and MRI together | 5.5% |
Based on these studies, it appears the miss rate is around 5-15% depending on the modality used. MRI is less likely to miss a stroke compared to CT. Using both MRI and CT together yields the lowest miss rates.
What are the consequences of a missed stroke on scans?
Some significant consequences can occur if a stroke is not detected accurately on the initial scans:
– Delay in treatment: Clot-busting drugs like tPA need to be given within 4.5 hours of stroke onset to be effective. Missing stroke diagnosis delays this treatment window.
– Progression of damage: Without swift treatment, damage can expand to wider areas of the brain as stroke progresses. Missed opportunities for early intervention can worsen outcomes.
– Misdiagnosis: Stroke symptoms may be incorrectly attributed to other conditions like vertigo, migraine or seizures if imaging is falsely negative.
– Repeat stroke risk: Underlying risk factors will not be identified and modified in someone mistakenly thought to not have a stroke. This raises recurrent stroke risk.
– Disability: Larger strokes that are missed initially can lead to greater residual disability due to poor early management.
– Death: Large strokes can be fatal. Missing these on scans removes the chance for lifesaving interventions.
How can the chances of missing a stroke be reduced?
Some ways to minimize the likelihood of strokes being overlooked on neuroimaging include:
– Perform baseline scans early but also repeat imaging at 6-12 hrs if stroke strongly suspected clinically but initial scan negative.
– Use both CT and MRI for comprehensive assessment when possible.
– Have scans read by experienced radiologists and double checked.
– Flag subtle early signs of infarct for radiologist to avoid overlooking.
– Check scan quality to avoid technical artifacts obscuring findings.
– Use standardized reporting checklists for radiologists to prevent interpretation errors.
– Provide radiologists clinical context of symptoms and timeline to direct their scan analysis.
– Implement training programs to improve detection skills of subtle findings.
Conclusion
While CT and MRI scans are extremely helpful for diagnosing strokes, they do not provide perfect accuracy. Subtle or early strokes can still be missed on neuroimaging under the right circumstances, with reported miss rates up to 15%. Missed strokes lead to dangerous delays in treatment and increased disability or death from not intervening early. Steps should be taken to maximize scan sensitivity and accuracy as well as repeat imaging when needed to minimize the chances of a devastating missed stroke diagnosis. Improved technology and radiologist training can help reduce missed stroke rates on scans. But some degree of human and technical fallibility remains inevitable. Maintaining a degree of clinical suspicion when imaging is unrevealing is therefore wise.