Intracranial CNS Infections: A Literature Review and Radiology Case Studies.

Acute infections of the intracranial central nervous system (CNS) often present as neurological emergencies, where missed or delayed diagnosis and treatment can be catastrophic to the patient. Accurate and timely identification of the underlying etiologies, which are critical in directing life-saving therapies, can be achieved through neuroimaging. This article will provide a thorough review of radiologic findings in common infections of the brain, from primarily compartmentalized infections of multimicrobial etiologies, to CNS manifestations of specific immunocompromised-selective pathogens, of herpes simplex virus, and of tuberculosis. We also briefly discuss the epidemiology, etiology, clinical features, treatment guidelines, complications, and long-term sequelae of these infections.

Acute Bowel Computed Tomography.

Acute abdominal pain is a common presenting complaint in the emergency department. Increasingly, computed tomography is utilized for evaluating these patients. Radiologists are therefore expected to be familiar with the pertinent clinical and radiologic information related to acute bowel pathology. This primer will review the need-to-know and latest updates related to computed tomography evaluation of acute bowel pathology.

Infectious and inflammatory diseases of the central nervous system-the spectrum of imaging findings and differential diagnosis.

The infectious and inflammatory diseases of the central nervous system (CNS) including the brain and spine can present with a wide spectrum of clinical symptoms, locations, and appearance. The purpose of this exhibit is to review the different patterns of their presentations, to illustrate their imaging characteristics and techniques, and to discuss their clinical features and pathology so that the correct diagnosis can be made and prompt intervention can be initiated on a timely fashion.

Extracranial internal carotid artery calcium volume measurement using computer tomography.

BACKGROUND: The extent of calcium volume in the carotid arteries of contrast-based computer tomography (CT) is a valuable indicator of stroke risk. This study presents an automated, simple and fast calcium volume computation system. Since the high contrast agent can sometimes obscure the presence of calcium in the CT slices, it is therefore necessary to identify these slices before the corrected volume can be estimated. METHODS: The system typically consists of segmenting the calcium region from the CT scan into slices based on Hounsfield Unit-based threshold, and subsequently computing the summation of the calcium areas in each slice. However, when the carotid volume has intermittently higher concentration of contrast agent, a dependable approach is adapted to correct the calcium region using the neighboring slices, thereby estimating the correct volume. Furthermore, mitigation is provided following the regulatory constraints by changing the system to semi-automated criteria as a fall back solution. We evaluate the automated and semi-automated techniques using completely manual calcium volumes computed based on the manual tracings by the neuroradiologist. RESULTS: A total of 64 patients with calcified plaque in the internal carotid artery were analyzed. Using the above algorithm, our automated and semi-automated system yields correlation coefficients (CC) of 0.89 and 0.96 against first manual readings and 0.90 and 0.96 against second manual readings, respectively. Using the t-test, there was no significant difference between the automated and semi-automated methods against manual. The intra-observer reliability was excellent with CC 0.98. CONCLUSIONS: Compared to automated method, the semi-automated method for calcium volume is acceptable and closer to manual strategy for calcium volume. Further work evaluating and confirming the performance of our semi-automated protocol is now warranted.

Silent Brain Infarction in Patients With Asymptomatic Carotid Artery Atherosclerotic Disease.

BACKGROUND AND PURPOSE: The relationship between carotid atherosclerosis and ipsilateral silent brain infarction (SBI) is unclear. We tested the hypothesis that extracranial internal carotid artery (ICA) stenosis is associated with a greater prevalence of SBI in the cerebral hemisphere ipsilateral to ICA disease compared with the unaffected, contralateral side. METHODS: We identified patients with unilateral extracranial ICA stenosis ≥50% on angiography by standard imaging criteria. We included patients with recent brain magnetic resonance imaging who had no previous history of stroke or transient ischemic attack. Blinded readers ascertained the presence of anterior circulation SBIs. SBI was defined as either a cavitary lacunar infarction in the white or deep gray matter or cortical infarction defined by T2 hyperintense signal in cortical gray matter. The Wilcoxon signed-rank test was used to compare SBI in the cerebral hemispheres and Cohen κ to assess inter-rater reliability of SBI evaluation. RESULTS: Among 104 patients, we found a higher prevalence of SBIs ipsilateral to ICA disease (33%) compared with the contralateral side (20.8%; P=0.0067). There was no significant difference in the prevalence of lacunar SBIs (including both white and deep gray matter) between hemispheres (P=0.109), but there was a significantly higher prevalence of cortical SBIs occurring downstream from ICA disease (P=0.0045). High inter-rater reliability was observed (κ=0.818). CONCLUSIONS: Patients with asymptomatic ICA disease demonstrate a higher prevalence of SBI downstream from their ICA atherosclerotic disease compared with the contralateral side but only of the cortical and not lacunar SBI subtype.

White Matter Diffusion Abnormalities in Carotid Artery Disease: A Systematic Review and Meta-Analysis.

BACKGROUND & PURPOSE: Abnormalities in apparent diffusion coefficient (ADC), fractional anisotropy (FA), and mean diffusivity (MD) values can be used to assess microstructural damage to white matter tracts and could represent a quantitative marker of chronic ischemia and thereby potentially serve as a stroke risk factor or a measure of existing subclinical ischemic disease burden. We performed a systematic review and 3 separate meta-analyses to evaluate the association between unilateral carotid steno-occlusion and ipsilateral ADC, FA, or MD abnormality. MATERIALS & METHODS: A comprehensive literature search evaluating the association of carotid disease and quantitative white matter diffusion imaging was performed. The included studies examined patients for ADC, FA, and MD values ipsilateral and contralateral to the site of carotid artery disease. Three meta-analyses using standardized mean differences with assessment of study heterogeneity were performed. RESULTS: Of the 2,920 manuscripts screened, 6 met eligibility for meta-analysis. Of the included manuscripts, 2 studied ADC values, 6 studied FA values, and 2 studied MD values. Our 3 meta-analyses showed standardized mean difference for ADC, FA, and MD values between cerebral hemispheres ipsilateral and contralateral to carotid artery disease site as 1.13 (95% CI: .79-1.47, P < .001), -.42 (95% CI: -.62 to -.21, P < .001), and .23 (95% CI: -.32 to -.77, P = .41), respectively. Measures of heterogeneity showed mild heterogeneity in the 3 meta-analyses. CONCLUSION: Carotid artery disease is associated with significant ADC and FA value changes, suggesting that carotid disease is associated with quantifiable white matter microstructural damage.

Detection of Symptomatic Carotid Plaque Using Source Data from MR and CT Angiography: A Correlative Study.

BACKGROUND: Carotid plaque MRI has been a useful method to characterize vulnerable atherosclerotic plaque elements. Recent investigations have suggested that source images from CT angiography (CTA) and MR angiography (MRA) can identify the simple high-risk features of symptom-producing carotid artery plaque. We studied the correlation and relative diagnostic accuracies of CTA and MRA source images in detecting symptomatic carotid artery plaque. METHODS: Subjects were eligible if they had carotid stenosis between 50 and 99% and had MRA and CTA exams performed within 10 days of one another. We measured the soft (non-calcified) plaque and hard (calcified) plaque thickness on CTA axial source images and intraplaque high-intensity signal (IHIS) on 3D-time-of-flight MRA source images in subjects. We assessed whether a correlation existed between increasing CTA soft plaque thicknesses and the presence of MRA IHIS using the Student's t-test. We calculated the differences in sensitivity and specificity measures of CTA and MRA source-imaging data with the occurrence of recent ipsilateral stroke or transient ischemic attack (TIA) as the reference standard. We also performed logistic regression analyses to evaluate the predictive strength of plaque showing both IHIS and increased CTA soft plaque thickness in predicting symptomatic disease status. RESULTS: Of 1994 screened patients, 48 arteries met the final inclusion criteria with MRA and CTA performed within 10 days of one another. The mean and median time between CTA and MRA exams were 2.0 days and 1 day, respectively. A total of 34 of 48 stenotic vessels (70.8%) were responsible for giving rise to ipsilateral stroke or TIA. CTA mean soft plaque thickness was significantly greater (4.47 vs. 2.30 mm, p < 0.0001) in patients with MRA-defined IHIS, while CTA hard plaque thickness was significantly greater (2.09 vs. 1.16 mm, p = 0.0134) in patients without MRA evidence of IHIS. CTA soft plaque thickness measurements were more sensitive than MRA IHIS (91.2 vs. 67.6%, p = 0.011) in detecting symptomatic plaque, while differences in specificity were not significantly different (p = 0.1573). In the subset of patients with both IHIS on MRA and plaque thickness >2.4 mm on CTA, the odds ratio of detecting symptomatic plaque, corrected for stenosis severity, was 45.3 (p < 0.0005). CONCLUSIONS: Unprocessed source images from CTA and MRA, which are routinely evaluated for clinical studies demonstrate the highly correlated presence of IHIS and increasing soft plaque thickness. In particular, plaque that shows high-risk features on both MRA and CTA are very strongly associated with symptom-producing carotid plaque. With further validation, such techniques are promising practical methods of extracting risk information from routine neck angiographic imaging.

Plaque echolucency and stroke risk in asymptomatic carotid stenosis: a systematic review and meta-analysis.

BACKGROUND AND PURPOSE: Ultrasonographic plaque echolucency has been studied as a stroke risk marker in carotid atherosclerotic disease. We performed a systematic review and meta-analysis to summarize the association between ultrasound-determined carotid plaque echolucency and future ipsilateral stroke risk. METHODS: We searched the medical literature for studies evaluating the association between carotid plaque echolucency and future stroke in asymptomatic patients. We included prospective observational studies with stroke outcome ascertainment after baseline carotid plaque echolucency assessment. We performed a meta-analysis and assessed study heterogeneity and publication bias. We also performed subgroup analyses limited to patients with stenosis ≥50%, studies in which plaque echolucency was determined via subjective visual interpretation, studies with a relatively lower risk of bias, and studies published after the year 2000. RESULTS: We analyzed data from 7 studies on 7557 subjects with a mean follow-up of 37.2 months. We found a significant positive relationship between predominantly echolucent (compared with predominantly echogenic) plaques and the risk of future ipsilateral stroke across all stenosis severities (0% to 99%; relative risk, 2.31; 95% confidence interval, 1.58-3.39; P<0.001) and in subjects with ≥50% stenosis (relative risk, 2.61; 95% confidence interval, 1.47-4.63; P=0.001). A statistically significant increased relative risk for future stroke was preserved in all additional subgroup analyses. No statistically significant heterogeneity or publication bias was present in any of the meta-analyses. CONCLUSIONS: The presence of ultrasound-determined carotid plaque echolucency provides predictive information in asymptomatic carotid artery stenosis beyond luminal stenosis. However, the magnitude of the increased risk is not sufficient on its own to iden tify patients likely to benefit from surgical revascularization.