From the Guidelines
Yes, posterior strokes can be missed on CT scans, particularly those occurring in the brainstem or cerebellum, with a low sensitivity of around 10%. This is due to the challenging visualization of the posterior fossa on CT scans, which contains the brainstem and cerebellum, caused by bone artifacts from the surrounding skull base that create beam-hardening effects, obscuring small infarcts 1. The tight space and compact neural structures in the posterior fossa also make subtle changes harder to detect.
Key Points to Consider
- CT scans have limited sensitivity for detecting acute ischemic changes, especially within the first few hours after stroke onset 1.
- MRI with diffusion-weighted imaging is the preferred imaging modality for suspected posterior circulation strokes, as it has much higher sensitivity (over 90%) compared to CT (less than 50% for posterior strokes) 1.
- If a posterior stroke is clinically suspected but the CT is negative, further imaging with MRI should be pursued, especially if symptoms include vertigo, ataxia, diplopia, or crossed sensory or motor deficits 1.
- Early diagnosis is crucial as posterior circulation strokes can rapidly progress and have high morbidity and mortality rates if not promptly identified and treated 1.
Recommendations for Clinical Practice
- MRI with diffusion-weighted imaging should be used as the primary imaging modality for suspected posterior circulation strokes, given its higher sensitivity compared to CT scans 1.
- Clinicians should be aware of the limitations of CT scans in detecting posterior strokes and consider further imaging with MRI if clinical suspicion remains high despite a negative CT scan 1.
- The use of MRI for in-hospital stroke evaluation can help change management and improve outcomes, particularly for patients with atypical stroke symptoms and a negative CT scan 1.
From the Research
CT Scan Limitations in Detecting Posterior Strokes
- Posterior strokes can be missed on CT scans due to various factors, including the location of the stroke and the timing of the scan 2.
- A study found that 37% of posterior strokes were initially misdiagnosed, compared to 16% of anterior strokes, highlighting the challenges in detecting posterior circulation strokes 2.
- The use of CT perfusion (CTP) imaging can improve the detection of posterior circulation strokes, but its diagnostic accuracy is still limited 3, 4.
Diagnostic Accuracy of CT Perfusion in Posterior Circulation Strokes
- A meta-analysis found that CTP has a higher pooled sensitivity (72%) compared to non-contrast computed tomography (NCCT) (25%), but a lower specificity (90% vs. 96%) 3.
- Another study found that CTP showed alterations in 64.5% of posterior circulation stroke patients, with mean transit time (MTT) being the most sensitive parameter 4.
- The effectiveness of CTP in detecting posterior circulation strokes can be influenced by various clinical factors, including atrial fibrillation, dyslipidemia, visual field deficits, and higher neurological deficit 4.
Clinical Implications
- The missed diagnosis of posterior circulation strokes can have significant clinical implications, including delayed treatment and poor outcomes 2.
- The use of CTP imaging can help improve the detection of posterior circulation strokes, but it should be interpreted in conjunction with clinical findings and other imaging modalities 3, 4.
- Further studies are needed to validate the prognostic capability of CTP-derived parameters in posterior circulation strokes and to develop more effective diagnostic strategies 3.