Eric S. Bartlett

Carotid Stenosis Index Revisited With Direct CT Angiography Measurement of Carotid Arteries to Quantify Carotid Stenosis

Background and Purpose— All carotid stenosis ratio methods are based on the inability of digital subtraction angiography to measure in millimeters. Each method has potential flaws. The Carotid Stenosis Index (CSI) was designed to reduce ambiguities of NASCET and ECST ratios. We test this method’s ability to correctly estimate carotid stenosis using direct computed tomography angiography millimeter measures of the carotid arteries. Methods— Two neuroradiologists reviewed computed tomography angiographies of 268 carotids with atherosclerotic disease. Millimeter measurements were obtained at the narrowest diameter of the residual stenotic lumen, actual carotid bulb diameter (at level of greatest stenosis), and common carotid artery. Pearson correlation compared the CSI estimate of the carotid bulb to the actual carotid bulb measurement. Ratio calculations of the stenosis were performed using (1) CSI carotid bulb estimate and (2) actual carotid bulb measurement as denominator data. A paired-sample Wilcoxon signed rank test compared the results of these 2 ratio measurements per carotid. Results— Interobserver variability was good to excellent (0.64 to 0.87). The CSI estimate of the carotid bulb size overestimated the measured carotid bulb by an average of 1.5 mm in a random distribution (correlation=0.39, N=151). Paired-sample Wilcoxon signed rank test demonstrated a significant difference between the 2 sets of ratios (z-value of −9.87, P<0.001). Conclusions— Direct measurement of carotid stenosis, vessel wall soft tissues, and computed tomography plaque imaging is now possible with the high-resolution anatomic data present in high-speed computed tomography angiography, alleviating the need for ratios and inaccurate mathematic estimations of carotid anatomy for carotid stenosis quantification.

Acute Hyperammonemic Encephalopathy in Adults: Imaging Findings

If you work in the hospital where organ transplants are done, you have probably seen this condition (even if you did not recognize it!). Unless identified and treated early, this encephalopathy has significant morbidity and mortality. In this short retrospective review, 4 patients with liver failure and plasma ammonia levels ranging from 55-168 umol/L were studied with MR imaging. The findings were significantly similar to those seen with anoxia, that is, diffuse gray and subcortical white matter involvement. The abnormalities were more pronounced in the insular cortex and cingulate gyri, a finding that helps distinguish acute hyperammonemic encephalopathy from other diseases. BACKGROUND AND PURPOSE: Acute hyperammonemic encephalopathy has significant morbidity and mortality unless promptly treated. We describe the MR imaging findings of acute hyperammonemic encephalopathy, which are not well-recognized in adult patients. MATERIALS AND METHODS: We retrospectively reviewed the clinical and imaging data and outcome of consecutive patients with documented hyperammonemic encephalopathy seen at our institution. All patients underwent cranial MR imaging at 1.5T. RESULTS: Four patients (2 women; mean age, 42 ± 13 years; range, 24–55 years) were included. Causes included acute fulminant hepatic failure, and sepsis with a background of chronic hepatic failure and post–heart-lung transplantation with various systemic complications. Plasma ammonia levels ranged from 55 to 168 μmol/L. Bilateral symmetric signal-intensity abnormalities, often with associated restricted diffusion involving the insular cortex and cingulate gyrus, were seen in all cases, with additional cortical involvement commonly seen elsewhere but much more variable and asymmetric. Involvement of the subcortical white matter was seen in 1 patient only. Another patient showed involvement of the basal ganglia, thalami, and midbrain. Two patients died (1 with fulminant cerebral edema), and 2 patients survived (1 neurologically intact and the other with significant intellectual impairment). CONCLUSIONS: The striking common imaging finding was symmetric involvement of the cingulate gyrus and insular cortex in all patients, with more variable and asymmetric additional cortical involvement. These specific imaging features should alert the radiologist to the possibility of acute hyperammonemic encephalopathy.

Magnetic resonance imaging of facial nerve schwannoma

This study characterizes the magnetic resonance (MR) appearances of facial nerve schwannoma (FNS). We hypothesize that the extent of FNS demonstrated on MR will be greater compared to prior computed tomography studies, that geniculate involvement will be most common, and that cerebellar pontine angle (CPA) and internal auditory canal (IAC) involvement will more frequently result in sensorineural hearing loss (SNHL).

Classification of Carotid Stenosis by Millimeter CT Angiography Measures: Effects of Prevalence and Gender

BACKGROUND AND PURPOSE: Previous studies quantifying moderate and severe carotid stenosis by direct millimeter measures on CT angiography (CTA) did not consider how prevalence and gender may influence classification cutoff values. MATERIALS AND METHODS: Three hundred nineteen carotid arteries were evaluated in consecutive patients with known or suspected carotid artery disease. Millimeter measures were obtained of the stenotic carotid bulb lumen and distal internal carotid artery (ICA). Interclass correlation coefficients (ICC) defined interobserver and intraobserver agreement. North American Symptomatic Carotid Endarterectomy Trial (NASCET)-style percent stenosis ratios were calculated per carotid artery and used in linear regression and receiver operating characteristic (ROC) curve analysis to define equivalent millimeter quantification and classification values. Likelihood ratios and prevalence-specific positive/negative predictive values (PPV/NPV) were calculated to determine the most appropriate millimeter cutoff values to classify stenosis. RESULTS: Interobserver agreement was excellent for stenosis measures (0.90) and good for distal ICA measures (0.79). Gender-specific regression curves and ROC curves indicated that millimeter stenosis is an excellent tool to quantify and classify carotid stenosis. Assuming a 10% prevalence of severe stenosis, we found that the cutoff value maximizing NPV and PPV was 1.1 mm for both genders (female: PPV = 86.2, NPV = 97.7; male: PPV = 83.2, NPV = 95.9). Assuming a 40% prevalence of moderate stenosis, we found that the cutoff values differed between genders: female = 2.0 mm (PPV = 91.3, NPV = 91.5), male = 2.1 mm (PPV = 91.6, NPV = 92.4). Specific millimeter cutoffs will vary depending upon the clinical scenario, prevalence, and gender. CONCLUSIONS: Direct millimeter stenosis measures are an excellent tool to classify moderate and severe carotid artery stenosis. Millimeter classification cutoff values that best approximate NASCET classifications vary depending on prevalence and gender.

Magnetic resonance imaging of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignant tumor that its the highest rates in Southeast Asia. It is a locally aggressive neoplasm that has a propensity for developing regional neck adenopathy. The main treatment modality consists primarily of radiation therapy. Cross-sectional imaging is important in order to achieve an accurate delineation of tumor extent, thereby facilitating both staging and treatment. MRI is currently considered the best modality to assess for NPC. The aim of this review is to provide a pictorial MRI review of NPC according to the recently released 7th edition of the International Union Against Cancer staging system.

Reproducibility of semi-automated measurement of carotid stenosis on CTA

PURPOSE To compare the reproducibility of semi-automated vessel analysis software to manual measurement of carotid artery stenosis on computed tomography angiography (CTA). METHODS Two observers separately analyzed 81 carotid artery CTAs using semi-automated vessel analysis software according to a blinded protocol. The software measured the narrowest stenosis in millimeters (mm), distal internal carotid artery (ICA) in mm, and calculated percent stenosis based on NASCET criteria. One observer performed this task twice on each carotid, the second analysis delayed two months in order to mitigate recall bias. Two other observers manually measured the narrowest stenosis in mm, distal ICA in mm, and calculated NASCET percent stenosis in a blinded fashion. Correlation coefficients were calculated for each group comparing the narrowest stenosis in mm, distal ICA in mm, and NASCET percent stenosis. RESULTS The semi-automated vessel analysis software provided excellent intraobserver correlation for narrowest stenosis in mm, distal ICA in mm, and NACSET percent stenosis (Pearson correlation coefficients of 0.985, 0.954, and 0.977 respectively). The semi-automated vessel analysis software provided excellent interobserver correlation (0.925, 0.881, and 0.892 respectively). The interobserver correlation for manual measurement was good (0.595, 0.625, and 0.555 respectively). There was a statistically significant difference in the interobserver correlation between the semi-automated vessel analysis software observers and the manual measurement observers (P < 0.001). CONCLUSION Semi-automated vessel analysis software is a highly reproducible method of quantifying carotid artery stenosis on CTA. In this study, semi-automated vessel analysis software determination of carotid stenosis was shown to be more reproducible than manual measurement.

Comparison of computed tomography angiography with digital subtraction angiography in the assessment of clipped intracranial aneurysms

Purpose: To examine whether computed tomography angiography (CTA) is comparable to digital subtraction angiography (DSA) in assessing clipped intracranial aneurysms. Materials and Methods: Retrospective collection of clipped aneurysms that had both CTA and DSA within 2 months of one another. Computed tomography angiograms were independently reviewed by 2 blinded neuroradiologists; rereviewed by one at least 4 months later. Each was classified as complete obliteration, neck remnant, or residual aneurysm. Parent vessel was classified as patent or occluded. Digital subtraction angiograms were reviewed in a similar manner by a third blinded neuroradiologist. Results: Forty-eight patients with 53 clipped aneurysms were collected. On DSA, 35 were completely obliterated, 10 neck remnants, and 8 residual aneurysms. The ability of CTA to detect residual aneurysms versus complete obliterations or neck remnants was excellent (mean sensitivity, 88%; specificity, 100%; positive predictive value [PPV], 100%; negative predictive value [NPV], 98%). The ability of CTA to detect neck remnants versus complete obliterations was poor (mean sensitivity, 20%; specificity, 99%; PPV, 83%; NPV, 81%). The CTAs were good at detecting parent vessel occlusion (mean sensitivity, 88%; specificity, 97%; PPV, 75%; NPV, 99%). Interrater and intrarater agreement was good to excellent for aneurysm and parent vessel assessment, with &kgr; values ranging from 0.6 to 1.0. Conclusions: Computed tomography angiography has high sensitivity and specificity for residual aneurysm detection and parent vessel occlusion. It is not accurate in neck remnant detection, although these were small and of uncertain clinical significance. This suggests that CTA is useful for follow-up of clipped aneurysms. However, given the potential to miss neck remnants or small residual aneurysms, it is recommended to perform initial DSA and CTA to select cases in which CTA follow-up is appropriate.

Falsely Claiming Use of NASCET Percentage Stenosis Method

We read with interest the report of Dr Anzidei and colleagues (1), which appeared in the May 2009 issue of Radiology, in which they compared steady-state contrast agent–enhanced magnetic resonance (MR) imaging with digital subtraction angiography (DSA) for the imaging of internal carotid artery (ICA) stenosis. This is an important contribution. Stenosis degrees were peripheral to this report, yet they were included. North American Symptomatic Carotid Endarterectomy Trial (NASCET) percentage stenosis methods (2–4) are referenced, with the explanation that percentage stenosis was used as a denominator beyond the bulb, where the walls are parallel, and was not The chief neuroradiology investigator (A.J.F.) for NASCET measured thousands of ICAs (2–4) in a consistent way as a balance to other inconsistent measurements (4,8–10). Yet, the so-called NASCET method for carotid stenosis calculation failed to enlist sufficient compliance. This is because many investigators choose ratio denominators from ICA locations that are too proximal, where the bulb is still tapering, contrary to the NASCET criteria to measure “where walls are parallel.” NASCET researchers never measured near occlusions, as it is fallacious and requires near occlusion interpretation before measuring. However, Dr Anzidei and colleagues ignore this in figure 1 (1). Researchers in scores of studies have also claimed to use NASCET criteria for percentage stenosis, yet the values they have produced have little relationship to NASCET. However, all of these investigators associate their findings with NASCET outcomes, with potentially many more surgeries resulting from overstated percentage stenosis. Radiologists are culpable for sending patients for surgery or stent placement on the basis of incorrect NASCET measurements and for the associated costs and risks. The ICA bulb is an anatomic aberration (2,4), which is larger than its outflow ICA. NASCET investigators adopted its method to provide the basis for a consistent measurement of percentage ICA stenosis, yet compliance with this method seems to be poor, with many authors using their own pseudo-NASCET methods. If the percentage stenosis denominator were eliminated and investigators and clinicians were to use the actual stenosis measurement in millimeters (7,13), now that it can easily be obtained, these ratio pitfalls that have been muddying things for years would be removed. References

Imaging and resectability issues of sinonasal tumors

Sinonasal tumors can invade into the critical structures of the anterior and central skull base. Although the determination of precise tumor histology is difficult with imaging, radiology is important in helping differentiate malignant from benign disease. Imaging helps to map the anatomical extent of intracranial and intraorbital tumor, which has important implications for staging, treatment and prognosis. Imaging also helps to facilitate and plan for craniofacial or endoscopic surgical approaches and radiation planning. This paper will review the locoregional invasion patterns for sinonasal tumors, with emphasis on their imaging features. The authors will discuss the implications for staging, resection potential, choice and details of radiotherapy with or without chemotherapy and prognosis. The imaging assessment of structures and compartments that are critical to the skull base team are highlighted: orbit, cavernous sinus, anterior cranial fossa dura/intracranial tumor, lateral frontal sinus, vascular tumor encasement, perineural tumor spread and tumor effect on the surrounding bony structures.

Measurement of Carotid Stenosis on Computed Tomographic Angiography: Reliability Depends on Postprocessing Technique

Purpose We previously demonstrated the validity of axial source (AxS) image quantification of computed tomographic angiography (CTA) visualized carotid stenosis. There is concern that AxS images may not accurately measure stenosis in patients with obliquely orientated stenosis and that measurements on axial oblique (AxO) multiplanar reformats (MPR), maximum intensity projections (MIP) images, or Doppler ultrasound (DUS) are superior. We tested the performance of AxS images against AxO MPRs, MIPs, and DUS techniques for stenosis quantification. Methods A total of 120 consecutive patients with CTA and DUS detected carotid disease were enrolled; carotids with occlusion, near occlusion, or stenosis <40% were excluded. Proximal and distal carotid diameters and North American Symptomatic Carotid Endarterectomy Trial (NASCET) style ratios were measured independently by 2 neuroradiologists on AxS, AxO, and MIP images on separate occasions in a blinded protocol. Intra- and interobserver agreements were determined for all measurements. The performance of different image types to identify ≥70% stenosis was assessed against a NASCET-style reference standard. Results Intra- and interobserver reliabilities for stenosis measurements were higher for both AxS (interclass correlation coefficients [ICC], 0.87–0.93 and 0.84–0.89) and AxO images (ICCs, 0.82–0.89 and 0.86–0.92) than for MIPs (ICCs, 0.66–0.86 and 0.79–0.82), respectively. Intra- and interobserver agreements on the NASCET ratio tended to be lower than proximal stenosis measurements. AxS and AxO image proximal stenosis measurements most accurately distinguished patients with ≥70% stenosis (0.90), followed by DUS (0.83) and MIP images (0.76). Conclusions A single AxS image stenosis measurement was highly reproducible and accurate in the estimation of carotid stenosis, which precluded the need for AxO MPRs.