Background and Purpose—Vertebral artery hypoplasia (VAH) is supposed to be a risk factor for posterior circulation ischemia (PCI), particularly in the territory of the posterior inferior cerebellar artery (PICA). The aim of our study was to determine whether VAH impedes perfusion in the dependent PICA territory even in the absence of manifest PCI. Methods—VA diameter was retrospectively measured in 934 consecutive patients who underwent whole-brain multimodal computed tomography because of suspected stroke. VAH was defined by a diameter of ≤2 mm and an asymmetry ratio of ≤1:1.7 of both VAs. We performed blinded computed tomography perfusion reading in patients with VAH without PCI (MRI-confirmed) and in control patients (ratio 1:2) with normal VAs. Four different perfusion maps were evaluated for a relative hypoperfusion in the PICA territory. Results—VAH was found in 146 of 934 patients (15.6%). It was more frequent on the right side (66.1%). Of 146 patients, 59 without PCI qualified for computed tomogra...

Vertebral Artery Hypoplasia Frequency and Effect on Cerebellar Blood Flow Characteristics

Acute stroke differential diagnosis: Stroke mimics.

The CT perfusion (CTP) imaging of brain has been established as a clinically useful tool in multimodality imaging of acute stroke. All abnormalities seen on perfusion CT are not specifically related to acute infarct. There are many neurologic diseases causing symptoms simulating cerebrovascular disease produce an alteration of brain perfusion and thus can result in perfusion CT abnormalities. There are many pitfalls and artifacts in acquiring the data, calculation of maps and choosing arterial input function. We analyze and classify all these aspects, to allow the technician and the radiologist to know exactly what to avoid and what to choose, and we indicate the way to improve the quality of examination. The knowledge of mimics and pitfalls in acute stroke imaging can be helpful in accurate interpretation of these examinations.

CT perfusion in acute stroke: Know the mimics, potential pitfalls, artifacts, and technical errors

BACKGROUND: CT perfusion (CTP) is used to estimate the extent of ischemic core and penumbra in patients with acute ischemic stroke. CTP reliability, however, is limited. This study aims to identify regions misclassified as ischemic core on CTP, using infarct on follow-up noncontrast CT. We aim to assess differences in volumetric and perfusion characteristics in these regions compared to areas that ended up as infarct on follow-up. MATERIALS AND METHODS: This study included 35 patients with >100 mm brain coverage CTP. CTP processing was performed using Philips software (IntelliSpace 7.0). Final infarct was automatically segmented on follow-up noncontrast CT and used as reference. CTP and follow-up noncontrast CT image data were registered. This allowed classification of ischemic lesion agreement (core on CTP: rMTT>/=145%, aCBV<2.0 ml/100g and infarct on follow-up noncontrast CT) and misclassified ischemic core (core on CTP, not identified on follow-up noncontrast CT) regions. False discovery ratio (FDR), defined as misclassified ischemic core volume divided by total CTP ischemic core volume, was calculated. Absolute and relative CTP parameters (CBV, CBF, and MTT) were calculated for both misclassified CTP ischemic core and ischemic lesion agreement regions and compared using paired rank-sum tests. RESULTS: Median total CTP ischemic core volume was 49.7ml (IQR:29.9ml-132ml); median misclassified ischemic core volume was 30.4ml (IQR:20.9ml-77.0ml). Median FDR between patients was 62% (IQR:49%-80%). Median relative mean transit time was 243% (IQR:198%-289%) and 342% (IQR:249%-432%) for misclassified and ischemic lesion agreement regions, respectively. Median absolute cerebral blood volume was 1.59 (IQR:1.43-1.79) ml/100g (P<0.01) and 1.38 (IQR:1.15-1.49) ml/100g (P<0.01) for misclassified ischemic core and ischemic lesion agreement, respectively. All CTP parameter values differed significantly. CONCLUSION: For all patients a considerable region of the CTP ischemic core is misclassified. CTP parameters significantly differed between ischemic lesion agreement and misclassified CTP ischemic core, suggesting that CTP analysis may benefit from revisions.

/pdf/characteristics-of-misclassified-ct-perfusion-ischemic-core-3izd35zf49.pdf

Characteristics of Misclassified CT Perfusion Ischemic Core in Patients with Acute Ischemic Stroke

CT perfusion (CTP) is part of the initial evaluation of stroke patients, allowing differentiation between infarcted tissue and the ischaemic penumbra and helping in the selection of patients for endovascular treatment. This study assessed the reliability of the qualitative evaluation CTP maps in defining the ischemic penumbra and identified potential pitfalls associated with this technique. We reviewed CTP scans of 45 consecutive patients admitted to our institution with anterior circulation acute ischaemic stroke. Two neuroradiologists performed qualitative evaluations of cerebral blood volume (CBV) and mean transit time (MTT) maps, using 24h follow-up non-contrast CT as surrogate marker for the area of definitive infarct. For each slice analyzed, the area of qualitative alteration in the CBV and MTT maps was classified as either being inferior, equal or superior to the area of infarct on the follow-up CT. Three out of 45 (7%) patients had admission CT CBV abnormalities larger than follow-up lesions; 34/45 (76%) patients had infarct areas smaller than initial MTT prolongation. In the group of patients with no recanalization 12/19 (63%) had infarct areas smaller than initial MTT lesion. CBV abnormality is a reliable marker for an irreversible ischaemic lesion, although rarely it may overestimate the ischaemic “core”, possibly due to delay in contrast arrival to the brain. In the majority of patients without recanalization, MTT overestimated final infarct areas, probably because it does not differentiate true “at risk” penumbra from benign oligaemia. Qualitative evaluation of CBV and MTT maps may overestimate the real ischaemic penumbra.

https://repositorio.chporto.pt/bitstream/10400.16/1864/1/Reliability%20of%20CT%20Perfusion.pdf

Reliability of CT Perfusion in the Evaluation of the Ischaemic Penumbra

Computed tomography (CT) plays a pivotal role in the diagnosis of acute stroke and in treatment decision making. CT perfusion imaging performed with intravenous iodinated contrast material allows calculation of the time to peak enhancement, mean transit time, and cerebral blood volume, important parameters for differentiating between an ischemic penumbra, which might benefit from intravascular therapy with thrombolytic agents, and infarcted tissue, which would not benefit from such therapy. Differentiation between the two entities is important because thrombolytic therapy is associated with an increased risk for intracranial hemorrhage. A finding of delay in peak enhancement or increased mean transit time in a region with normal or only slightly abnormal cerebral blood volume is suggestive of an ischemic penumbra; however, accurate interpretation of the CT perfusion parameters may be difficult in the presence of a cerebrovascular anatomic variant or physiologic condition that produces benign oligemia leading to a false appearance of penumbra. For this reason, CT perfusion parameters must be correlated with the clinical history and findings at unenhanced head CT, angiography or CT angiography, and diffusion-weighted magnetic resonance imaging. The authors identify five possible causes of false penumbras, each of which produces a different pattern at imaging: upstream flow restriction, evolution of ischemic change, vascular dysregulation, positioning of the patient's head at an angle during image acquisition, and variant anatomy in the circle of Willis. Familiarity with the imaging patterns and causes of false penumbras may increase the radiologist's confidence in diagnosis and help avoid costly errors in treatment.

Recognizing false ischemic penumbras in CT brain perfusion studies.

Hemihypoplasia and venous anomalies associated with linear nevus sebaceous syndrome

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Recognizing false ischemic penumbras in CT brain perfusion studies.

Hemihypoplasia and venous anomalies associated with linear nevus sebaceous syndrome