How to avoid false positive hyperdense middle cerebral artery sign detection in ischemic stroke

MR microscopy to assess clot composition following mechanical thrombectomy predicts recanalization and clinical outcome

BACKGROUND

Mechanical thrombectomy (MT) is the standard of care for patients with a stroke and large vessel occlusion. Clot composition is not routinely assessed in clinical practice as no specific diagnostic value is attributed to it, and MT is performed in a standardized 'non-personalized' approach. Whether different clot compositions are associated with intrinsic likelihoods of recanalization success or treatment outcome is unknown.

METHODS

We performed a prospective, non-randomized, single-center study and analyzed the clot composition in 60 consecutive patients with ischemic stroke undergoing MT. Clots were assessed by ex vivo multiparametric MRI at 9.4 T (MR microscopy), cone beam CT, and histopathology. Clot imaging was correlated with preinterventional CT and clinical data.

RESULTS

MR microscopy showed red blood cell (RBC)-rich (21.7%), platelet-rich (white,38.3%) or mixed clots (40.0%) as distinct morphological entities, and MR microscopy had high accuracy of 95.4% to differentiate clots. Clot composition could be further stratified on preinterventional non-contrast head CT by quantification of the hyperdense artery sign. During MT, white clots required more passes to achieve final recanalization and were not amenable to contact aspiration compared with mixed and RBC-rich clots (maneuvers: 4.7 vs 3.1 and 1.2 passes, P<0.05 and P<0.001, respectively), whereas RBC-rich clots showed higher probability of first pass recanalization (76.9%) compared with white clots (17.4%). White clots were associated with poorer clinical outcome at discharge and 90 days after MT.

CONCLUSION

Our study introduces MR microscopy to show that the hyperdense artery sign or MR relaxometry could guide interventional strategy. This could enable a personalized treatment approach to improve outcome of patients undergoing MT.

Dual-Energy Computed Tomography Virtual Noncalcium Imaging of Intracranial Arteries in Acute Ischemic Stroke: Differentiation Between Acute Thrombus and Calcification

OBJECTIVE

Hyperdense artery sign (HAS) on noncontrast brain computed tomography (CT) indicates an acute thrombus within the cerebral artery. It is a valuable imaging biomarker for diagnosing large-vessel occlusion; however, its identification may be challenging with the presence of vascular calcification. Dual-energy CT virtual noncalcium (VNCa) imaging using a 3-material decomposition algorithm is helpful for differentiating between calcification and hemorrhage. This study aimed to clarify the potential of VNCa imaging for differentiating HAS from vascular calcification.

METHODS

Patients with acute ischemic stroke and large-vessel occlusion identified on MR angiography, who also underwent noncontrast dual-energy CT, were included. The 80 kV/Sn 140 kV mixed images, with a weighting factor of 0.4, were considered 120 kVp-equivalent images. Postprocessing using a 3-material decomposition algorithm to differentiate between calcium (Ca), cerebrospinal fluid, and hemorrhage was performed via a commercially available 3-dimensional workstation. A mixed image, VNCa image, color-coded Ca image, and color-coded Ca image with VNCa image overlay (color-coded Ca-overlay image) were obtained, and axial reconstruction with a 1-mm slice thickness was performed for each image type. Two experienced neuroradiologists conducted imaging evaluations in consensus.

RESULTS

Thirty-four patients (mean age, 76.0 years; 21 male and 13 female patients) were included. The mixed and VNCa images revealed an HAS (indicating an acute clot) corresponding to the large-vessel occlusion site in 30 patients. Among them, the VNCa and color-coded Ca-overlay images enabled clear differentiation between the acute thrombus and adjacent vessel wall calcification in 5 patients. Among the other 4 patients, the VNCa, Ca-overlay, and Ca images identified calcified cerebral emboli in the M1 segment in 1 patient. For the other 3 patients, no high attenuation corresponding to magnetic resonance angiography findings was observed in any of the mixed, VNCa, Ca-overlay, or Ca images.

CONCLUSIONS

VNCa and color-coded Ca-overlay images obtained via dual-energy brain CT enabled differentiation of acute thrombus from vessel wall calcification and calcified cerebral emboli in patients with acute ischemic stroke.

The middle cerebral artery density and ratio for the diagnosis of acute ischaemic stroke in the Emergency Department

PURPOSE

Non-contrast computed tomography (ncCT) is the first-line imaging modality for acute ischaemic stroke diagnosis. Recognition of the early diagnostic signs of a stroke on computed tomography (CT) is crucial. The hyperdense middle cerebral artery (MCA) sign is one of these findings. We investigated the diagnostic utility of absolute MCA density (MCAD) in patients with acute MCA stroke confirmed with diffusion-weighted magnetic resonance imaging (dwMRI).

METHODS

We retrospectively included all patients who presented to the Emergency Department with symptoms related to an acute stroke and confirmed with a dwMRI and ncCT to this diagnostic case-control study. An expert radiologist with more than four years of experience in neuroradiology re-evaluated all ncCT images. The evaluation of MCAD and ratio were measured on axial images in Hounsfield units (HU).

RESULTS

We included 407 patients in our study (MCA infarction: 55%, n = 225; Control: 45%, n = 182). We calculated the threshold for the highest sensitivity (20%) and specificity (94%) as 49 HU with the Youden J index test for MCAD and as 1.1 for MCAD ratio (sensitivity 20% and specificity 95%). MCAD >49 HU or MCAD ratio >1.1 alone or joint use of MCAD >47 HU and MCAD ratio >1.1 are useful markers to confirm the diagnosis of MCA AIS with a specificity of at least 94%. Higher MCAD values are associated with larger infarction volumes.

CONCLUSION

MCAD and MCAD ratio can be used to identify patients who need early treatment, especially in situations where computed tomography angiogram or dwMRI are not readily available.

CT assessment of the increased density of cerebral vessels in plateau region

In this study, the relationship between the brain parenchymal density, the cerebral vessel density, the mean corpuscular hemoglobin (MCH) content, the mean corpuscular hemoglobin concentration (MCHC), and the morbidity associated with lacunar infarction of residents living in either the plains or the plateau regions were analyzed and compared for their potential clinical implications. Clinical data from the brain CT scans of individuals living in either the plain or plateau regions (129 each) were collected. Specifically, the CT values for basal ganglia, the middle cerebral artery, and the superior sagittal sinus, along with the number of patients with lacunar infarction, were collected. In addition, the MCH and MCHC values were measured in blood samples collected within 48 h following the CT scans. For statistical analysis, an independent sample t-test, Pearson's correlation test (permutation test), and Chi-squared test were employed. The inhabitants of the plateau had a significantly higher CT value of basal ganglia, the middle cerebral artery, and superior sagittal sinus and also higher levels of MCH and MCHC in the blood (ps < 0.001) than the inhabitants of the plains region. Further, there was a significant positive correlation between the three aforementioned CT values and the MCH and MCHC findings. However, no significant differences were found in the morbidity of lacunar infarction between these two regions (p > 0.05). The inhabitants in the plateau have a significantly higher brain parenchymal density, higher CT value for cerebral vessels density, and higher blood MCH and MCHC levels in comparison with individuals occupying the plains. Concurrently, the parenchymal density and the CT values are shown to be positively correlated with the MCH and MCHC content in the blood.

Attempt to delineate occluded arteries with initial plain computed tomography in acute cerebral arterial occlusion

BACKGROUND

We used initial plain computed tomography to delineate acutely occluded internal carotid arteries or horizontal segments of middle cerebral arteries. If affected arteries could be delineated using initial plain computed tomography, useful information might be obtained that could support endovascular thrombectomies.

METHODS

In 15 patients with occluded internal carotid arteries or horizontal segments of middle cerebral arteries, the affected middle cerebral artery was automatically traced using the extender function for blood vessel tracing with reference to the default value (window setting, 40; window width, 90) on Ziostation 2 (Ziosoft Inc., Tokyo, Japan) based on initial plain computed tomography data.

RESULTS

The horizontal and sylvian segments of the middle cerebral artery were delineated in 15 and nine patients, respectively, based on plain computed tomography volume data. Images of occluded vessels delineated by plain computed tomography closely correlated with digital subtraction angiography.

CONCLUSIONS

Initial plain computed tomography combined with a new generation workstation enabled the rapid delineation of occluded segments of intracranial vessels and could provide useful information that might improve the safety of endovascular thrombectomy.

Stroke scan agnosia - What radiologists may not see

OBJECTIVE

Neuroimaging helps neurologists make accurate diagnoses. We used a multidisciplinary review system to search for perceptual discrepancies in stroke lesions. We sought to identify recurrent pitfalls in the detection of neuroimaging stroke lesions.

PATIENTS AND METHODS

Patients were selected from a neuroimaging database of second opinions if cerebrovascular lesions had been missed at initial reporting. Patient demographics, scanning modality and stroke type were recorded.

RESULTS

A neuroradiologist second opinion was provided for 1336 patients. Forty-four patients, 18 women and 26 men, mean age 59.9 (SD 14.2) years, were identified in whom a vascular lesion was not detected on initial reporting. The lesions included cerebellar infarcts in 17 patients (bilateral in 7), pontine infarction/ischaemia (n=5), pontine and cerebellar lesions (n=1) and spinal infarction (n=1). Supratentorial infarction occurred in 10 patients of which 3 were thalamic infarcts. Vessel abnormalities were present in 8 patients (hyperdense vessel n=3, dissection n=3, middle cerebral artery occlusion on CTA n=1 and cerebral venous sinus thrombosis n=1). Convexity subarachnoid hemorrhage was missed and a subdural hematoma was not identified in one patient. In 10 (23 %) patients the missed lesions occurred solely on CT brain scanning. The missed lesions were symptomatic in 28 (64 %) patients and presentations were acute in 14 (32 %) patients.

CONCLUSION

Some cerebrovascular lesions are prone to perceptual errors with CT and MRI brain scanning. Radiologists and neurologists should be aware that posterior fossa lesions (particularly in the cerebellum and pons) and hyperdense vessel signs may be missed. Better identification of radiological cerebrovascular lesions should enhance management of acute and chronic stroke patients.

Neuroimaging of Acute Stroke

Acute stroke is the clinical manifestation of disrupted blood flow or bleeding in the central nervous system. Imaging supports the clinical diagnosis and can aide in acute treatment decision making and guide information on prognosis. Features that are delineated include the parenchyma and the blood vessels. Parenchymal characteristics include early ischemic changes, established infarct and tissue at risk (penumbra), and hemorrhage. Vessel pathology includes arterial and venous steno-occlusive disease and vascular malformations. In the presence of a vessel occlusion, vessel imaging can assess collateral flow. This article outlines the role of neuroimaging as applied to patients presenting with acute stroke.