Spatial relational learning and memory abilities do not differ between men and women in a real-world, open-field environment

This study assesses gender differences in spatial and non-spatial relational learning and memory in adult humans behaving freely in a real-world, open-field environment. In Experiment 1, we tested the use of proximal landmarks as conditional cues allowing subjects to predict the location of rewards hidden in one of two sets of three distinct locations. Subjects were tested in two different conditions: (1) when local visual cues marked the potentially-rewarded locations, and (2) when no local visual cues marked the potentially-rewarded locations. We found that only 17 of 20 adults (8 males, 9 females) used the proximal landmarks to predict the locations of the rewards. Although females exhibited higher exploratory behavior at the beginning of testing, males and females discriminated the potentially-rewarded locations similarly when local visual cues were present. Interestingly, when the spatial and local information conflicted in predicting the reward locations, males considered both spatial and local information, whereas females ignored the spatial information. However, in the absence of local visual cues females discriminated the potentially-rewarded locations as well as males. In Experiment 2, subjects (9 males, 9 females) were tested with three asymmetrically-arranged rewarded locations, which were marked by local cues on alternate trials. Again, females discriminated the rewarded locations as well as males in the presence or absence of local cues. In sum, although particular aspects of task performance might differ between genders, we found no evidence that women have poorer allocentric spatial relational learning and memory abilities than men in a real-world, open-field environment.

Autoimmunity-Associated LYP-W620 Does Not Impair Thymic Negative Selection of Autoreactive T Cells.

A C1858T (R620W) variation in the PTPN22 gene encoding the tyrosine phosphatase LYP is a major risk factor for human autoimmunity. LYP is a known negative regulator of signaling through the T cell receptor (TCR), and murine Ptpn22 plays a role in thymic selection. However, the mechanism of action of the R620W variant in autoimmunity remains unclear. One model holds that LYP-W620 is a gain-of-function phosphatase that causes alterations in thymic negative selection and/or thymic output of regulatory T cells (Treg) through inhibition of thymic TCR signaling. To test this model, we generated mice in which the human LYP-W620 variant or its phosphatase-inactive mutant are expressed in developing thymocytes under control of the proximal Lck promoter. We found that LYP-W620 expression results in diminished thymocyte TCR signaling, thus modeling a "gain-of-function" of LYP at the signaling level. However, LYP-W620 transgenic mice display no alterations of thymic negative selection and no anomalies in thymic output of CD4(+)Foxp3(+) Treg were detected in these mice. Lck promoter-directed expression of the human transgene also causes no alteration in thymic repertoire or increase in disease severity in a model of rheumatoid arthritis, which depends on skewed thymic selection of CD4(+) T cells. Our data suggest that a gain-of-function of LYP is unlikely to increase risk of autoimmunity through alterations of thymic selection and that LYP likely acts in the periphery perhaps selectively in regulatory T cells or in another cell type to increase risk of autoimmunity.

Flow targeted 3D steady-state free-precession coronary MR angiography: comparison of three different imaging approaches.

PURPOSE: To compare 3 different flow targeted magnetization preparation strategies for coronary MR angiography (cMRA), which allow selective visualization of the vessel lumen. MATERIAL AND METHODS: The right coronary artery of 10 healthy subjects was investigated on a 1.5 Tesla MR system (Gyroscan ACS-NT, Philips Healthcare, Best, NL). A navigator-gated and ECG-triggered 3D radial steady-state free-precession (SSFP) cMRA sequence with 3 different magnetization preparation schemes was performed referred to as projection SSFP (selective labeling of the aorta, subtraction of 2 data sets), LoReIn SSFP (double-inversion preparation, selective labeling of the aorta, 1 data set), and inflow SSFP (inversion preparation, selective labeling of the coronary artery, 1 data set). Signal-to-noise ratio (SNR) of the coronary artery and aorta, contrast-to-noise ratio (CNR) between the coronary artery and epicardial fat, vessel length and vessel sharpness were analyzed. RESULTS: All cMRA sequences were successfully obtained in all subjects. Both projection SSFP and LoReIn SSFP allowed for selective visualization of the coronary arteries with excellent background suppression. Scan time was doubled in projection SSFP because of the need for subtraction of 2 data sets. In inflow SSFP, background suppression was limited to the tissue included in the inversion volume. Projection SSFP (SNR(coro): 25.6 +/- 12.1; SNR(ao): 26.1 +/- 16.8; CNR(coro-fat): 22.0 +/- 11.7) and inflow SSFP (SNR(coro): 27.9 +/- 5.4; SNR(ao): 37.4 +/- 9.2; CNR(coro-fat): 24.9 +/- 4.8) yielded significantly increased SNR and CNR compared with LoReIn SSFP (SNR(coro): 12.3 +/- 5.4; SNR(ao): 11.8 +/- 5.8; CNR(coro-fat): 9.8 +/- 5.5; P < 0.05 for both). Longest visible vessel length was found with projection SSFP (79.5 mm +/- 18.9; P < 0.05 vs. LoReIn) whereas vessel sharpness was best in inflow SSFP (68.2% +/- 4.5%; P < 0.05 vs. LoReIn). Consistently good image quality was achieved using inflow SSFP likely because of the simple planning procedure and short scanning time. CONCLUSION: Three flow targeted cMRA approaches are presented, which provide selective visualization of the coronary vessel lumen and in addition blood flow information without the need of contrast agent administration. Inflow SSFP yielded highest SNR, CNR and vessel sharpness and may prove useful as a fast and efficient approach for assessing proximal and mid vessel coronary blood flow, whereas requiring less planning skills than projection SSFP or LoReIn SSFP.

Systematic and exclusive use of intravascular ultrasound for endovascular aneurysm repair - the Lausanne experience.

Five years of experience with endovascular infrarenal aneurysm repair at our institution is reviewed. Implantation of endoprostheses in 88 patients has been performed by surgeons using exclusively intravascular ultrasound (IVUS) and fluoroscopy. IVUS identified the target site of deployment in all cases. In-hospital morbidity was 22% (19/88). Two percent mortality (2/88) and 5% early conversion (4/88) as a consequence of type I endoleaks were noted only in the first 53 patients with early devices (NS). Early endoleaks were present in 36% (32/88) including twenty-two type I, five type II and five type III endoleaks. Proximal endoleaks were associated with early devices (P<0.001), and technical difficulties with deployment. Tube grafts used in the beginning, performed poorly with 54% (7/13) type I endoleaks. Endoleaks diminished to 10% (9/88) by spontaneous closure and secondary endovascular procedures that were necessary in 24% (21/88) and consisted of coil embolization/cuff extension (9), late conversion (6), and limb recanalization or femoral cross-over bypass (6). Endovascular aneurysm repair using IVUS is a valid alternative technique. Improved devices and systematic use of bifurcated endoprostheses for infrarenal aneurysms reduce the occurrence of type I endoleaks.

Coronary magnetic resonance angiography in adolescents and young adults with kawasaki disease.

BACKGROUND: In patients with Kawasaki disease, serial evaluation of the distribution and size of coronary artery aneurysms (CAA) is necessary for risk stratification and therapeutic management. Although transthoracic echocardiography is often sufficient for this purpose initially, visualization of the coronary arteries becomes progressively more difficult as children grow. We sought to prospectively compare coronary magnetic resonance angiography (MRA) and x-ray coronary angiography findings in patients with CAA caused by Kawasaki disease. METHODS AND RESULTS: Six subjects (age 10 to 25 years) with known CAA from Kawasaki disease underwent coronary MRA using a free-breathing T2-prepared 3D bright blood segmented k-space gradient echo sequence with navigator gating and tracking. All patients underwent x-ray coronary angiography within a median of 75 days (range, 1 to 359 days) of coronary MRA. There was complete agreement between MRA and x-ray angiography in the detection of CAA (n=11), coronary artery stenoses (n=2), and coronary occlusions (n=2). Excellent agreement was found between the 2 techniques for detection of CAA maximal diameter (mean difference=0.4 +/- 0.6 mm) and length (mean difference=1.4 +/- 1.6 mm). The 2 methods showed very similar results for proximal coronary artery diameter (mean difference=0.2 +/- 0.5 mm) and CAA distance from the ostia (mean difference=0.1 +/- 1.5 mm). CONCLUSION: Free-breathing 3D coronary MRA accurately defines CAA in patients with Kawasaki disease. This technique may provide a non-invasive alternative when transthoracic echocardiography image quality is insufficient, thereby reducing the need for serial x-ray coronary angiography in this patient group.

Clinical results of autologous infrainguinal revascularization using grafts originating distal to the femoral bifurcation in patients with mild inflow disease.

AIM: Chronic critical limb ischemia (CLI) often requires venous bypass grafting to distal arterial segments. However, graft patency is influenced by the length and quality of the graft and occasionally patients may have limited suitable veins. We investigated short distal bypass grafting from the superficial femoral or popliteal artery to the infrapopliteal, ankle or foot arteries, despite angiographic alterations of inflow vessels, providing that invasive pressure measurement at the site of the planned proximal anastomosis revealed an inflow-brachial pressure difference of <or=10 mmHg. METHODS: Four hundred and twenty-three consecutive infrainguinal bypass grafts were performed for CLI between June, 1999 and November, 2002 at our institution. All patients underwent preoperative clinical examination, arteriography and assessment of the veins by duplex ultrasound. The study group are patients in whom the proximal and distal anastomoses of the bypass are below the femoral bifurcation and the popliteal artery, respectively. Invasive arterial pressure measurements were recorded at the level of the planned proximal anastomosis which was performed at that level if the difference of the inflow-brachial pressure was <or=10 mmHg, irrespective of angiographic alterations of the inflow vessels proximal to the planned anastomosis. All patients had a clinical follow-up included a duplex examination of their graft, at 1 week, 3, 9 and 12 months and, thereafter, annually. No patient was lost to follow-up. RESULTS: Sixty-seven patients underwent 71 short distal bypass grafts in 71 limbs with reversed saphenous vein grafts in 52, in situ saphenous veins in 11, reversed cephalic vein in 1 and composite veins in 7, respectively. Surgical or endovascular interventions to improve inflow were required in 4 limbs (5.6%). The mean follow-up time was 22.5 months and the two-year survival was 92.5%. Primary and secondary patency rates at 2 years were 73% and 93%, respectively, and the limb salvage rate was 98.5%. CONCLUSION: In appropriately selected patients, short distal venous bypass grafts can be performed with satisfactory patency and limb salvage rates even in the presence of morphologic alterations of the inflow vessels providing that these are not hemodynamically significant, or can be corrected intraoperatively.

The "open" chimney graft technique for juxtarenal aortic aneurysms with discrepant renal arteries.

OBJECTIVES: A straightforward original Chimney Graft (CG) protocol has been developed at our institution in selected cases of juxtarenal aortic aneurysm (JRAA). The aim of this study was to present our clinical experience of consecutive series with use of uncovered self-expanding stent (SES) as "Open Chimney" (OCh) in the endovascular repair (EVAR) of JRAA. METHODS: A standard endograft with suprarenal fixation struts is delivered with its proximal covered edge just below the highest RA in JRAA presenting the ostium of the two renal arteries at a different aortic level and the distance between the highest renal artery and the beginning of the aneurysm (improved landing zone) ≥10 mm. The low-lying renal artery is maintained patent by the OCh graft (standard SES) delivered from left brachial access (6 Fr). All clinical, anatomical, and operative data were prospectively collected and retrieved for the study analysis. RESULTS: From July 2010 to November 2012, OCh EVAR was offered to 22 consecutive patients considered unfit for JRAA open repair. All procedures were technically successful with aneurysm exclusion and patent OCh graft. One small perioperative type Ia endoleak spontaneously disappeared at the 3-month CT control. One patient died because of acute decompensated heart failure. One patient presented a left hemispheric stroke. The median follow-up of 18 months (range 7-35) showed aneurysm exclusion in all patients without type I and III endoleaks, SES stenosis, and/or renal impairment. CONCLUSIONS: OCh-EVAR is a straightforward technique that can be employed in selected cases of JRAA, avoiding the more complex and expensive fenestrated EVAR.

Depositional models of lacustrine evaporites in the SE margin of the Ebro basin (Paleogene, NE Spain)

An important evaporitic sedimentation occurred during the Paleogene (Eocene to lower Oligocene) in the Barberà sector of the southeastern margin of the Tertiary Ebro Basin. This sedimentation took place in shallow lacustrine environments and was controlled by a number of factors: 1) the tectonic structuration of the margin; 2) the high calcium sulphate content in the meteoric waters coming from the marginal reliefs; 3) the semiarid climate; and 4) the development of large alluvial fans along the basin margin, which also conditioned the location of the saline lakes. The evaporites are currently composed of secondary gypsum in surface and anhydrite at depth. There are, however, vestiges of the local presence of sodium sulphates. The evaporite units, with individual thicknesses ranging between 50 and 100 m, are intercalated within various lithostratigraphic formations and exhibit a paleogeographical pattern. The units located closer to the basin margin are characterized by a massive gypsum lithofacies (originally, bioturbated gypsum) bearing chert, and also by meganodular gypsum locally (originally, meganodules of anhydrite) in association with red lutites and clastic intercalations (gypsarenites, sandstones and conglomerates). Chert, which is only linked to the thickest gypsum layers, seems to be an early diagenetic, lacustrine product. Cyclicity in these proximal units indicates the progressive development of lowsalinity, lacustrine bodies on red mud flats. At the top of some cycles, exposure episodes commonly resulted in dissolution, erosion, and the formation of edaphic features. In contrast, the units located in a more distal position with regard to the basin margin are formed by an alternation of banded-nodular gypsum and laminated gypsum layers in association with grey lutites and few clastic intercalations. These distal units formed in saline lakes with a higher ionic concentration. Exposure episodes in these lakes resulted in the formation of synsedimentary anhydrite and sabkha cycles. In some of these units, however, outer rims characterized by a lithofacies association similar to that of the proximal units occur (nodular gypsum, massive gypsum and chert nodules).

An essential role for the stalk region of CD8 beta in the coreceptor function of CD8.

The CD8alphabeta heterodimer is integral to the selection of the class I-restricted lineage in the thymus; however, the contribution of the CD8beta chain to coreceptor function is poorly understood. To understand whether the CD8beta membrane proximal stalk region played a role in coreceptor function, we substituted it with the corresponding sequence from the CD8alpha polypeptide and expressed the hybrid molecule in transgenic mice in place of endogenous CD8beta. Although the stalk-swapped CD8beta was expressed on the cell surface as a disulfide-bonded heterodimer at equivalent levels of expression to an endogenous CD8beta molecule, it failed to restore selection of CD8(+) class I MHC-restricted T cells and it altered the response of peripheral T cells. Thus, the stalk region of the CD8beta polypeptide has an essential role in ensuring functionality of the CD8alphabeta heterodimer and its replacement compromises the interaction of CD8 with peptide-MHC complexes.

Coexpression of the T-cell receptor constant alpha domain triggers tumor reactivity of single-chain TCR-transduced human T cells.

Transfer of tumor antigen-specific T-cell receptors (TCRs) into human T cells aims at redirecting their cytotoxicity toward tumors. Efficacy and safety may be affected by pairing of natural and introduced TCRalpha/beta chains potentially leading to autoimmunity. We hypothesized that a novel single-chain (sc)TCR framework relying on the coexpression of the TCRalpha constant alpha (Calpha) domain would prevent undesired pairing while preserving structural and functional similarity to a fully assembled double-chain (dc)TCR/CD3 complex. We confirmed this hypothesis for a murine p53-specific scTCR. Substantial effector function was observed only in the presence of a murine Calpha domain preceded by a TCRalpha signal peptide for shuttling to the cell membrane. The generalization to a human gp100-specific TCR required the murinization of both C domains. Structural and functional T-cell avidities of an accessory disulfide-linked scTCR gp100/Calpha were higher than those of a dcTCR. Antigen-dependent phosphorylation of the proximal effector zeta-chain-associated protein kinase 70 at tyrosine 319 was not impaired, reflecting its molecular integrity in signaling. In melanoma-engrafted nonobese diabetic/severe combined immunodeficient mice, adoptive transfer of scTCR gp100/Calpha transduced T cells conferred superior delay in tumor growth among primary and long-term secondary tumor challenges. We conclude that the novel scTCR constitutes a reliable means to immunotherapeutically target hematologic malignancies.

Ascending aorta measurements as assessed by ECG-gated multi-detector computed tomography: a pilot study to establish normative values for transcatheter therapies

The aim of this study was to provide an insight into normative values of the ascending aorta in regards to novel endovascular procedures using ECG-gated multi-detector CT angiography. Seventy-seven adult patients without ascending aortic abnormalities were evaluated. Measurements at relevant levels of the aortic root and ascending aorta were obtained. Diameter variations of the ascending aorta during cardiac cycle were also considered. Mean diameters (mm) were as follows: LV outflow tract 20.3 +/- 3.4, coronary sinus 34.2 +/- 4.1, sino-tubular junction 29.7 +/- 3.4 and mid ascending aorta 32.7 +/- 3.8 with coefficients of variation (CV) ranging from 12 to 17%. Mean distances (mm) were: from the plane passing through the proximal insertions of the aortic valve cusps to the right brachio-cephalic artery (BCA) 92.6 +/- 11.8, from the plane passing through the proximal insertions of the aortic valve cusps to the proximal coronary ostium 12.1 +/- 3.7, and between both coronary ostia 7.2 +/- 3.1, minimal arc of the ascending aorta from left coronary ostium to right BCA 52.9 +/- 9.5, and the fibrous continuity between the aortic valve and the anterior leaflet of the mitral valve 14.6 +/- 3.3, CV 13-43%. Mean aortic valve area was 582.0 +/- 131.9 mm(2). The variation of the antero-posterior and transverse diameters of the ascending aorta during the cardiac cycle were 8.4% and 7.3%, respectively. Results showed large inter-individual variations in diameters and distances but with limited intra-individual variations during the cardiac cycle. A personalized approach for planning endovascular devices must be considered.

Secondary prevention of osteoporotic fractures : room for improvement

Résumé : Introduction : l'ostéoporose est une maladie fréquente, invalidante, sous-diagnostiquée et sous-traitée, alors qu'il existe des évidences cliniques, densitométriques et biologiques de l'efficacité de la prévention secondaire. Matériel et méthode : dans cette étude, nous décrivons les habitudes de prescription de traitements en prévention secondaire dans les 6 mois qui suivent une fracture de fragilité et définissons les catégories de femmes recevant ou non un traitement, selon le type de fractures, les antécédents fracturaires et les données socio-démographiques. Il s'agit d'une étude suisse de cohorte, prospective de 7609 femmes de 70 ans et plus, suivies de 1998 à 2000. Deux groupes de patientes ont été analysés : celles avec un événement fracturaire durant le suivi (3 sous-groupes de fractures ont été considérés fractures vertébrales, fractures du radius distal et fractures de l'humérus proximal) et celles sans fractures durant le suivi (groupe contrôle). La détermination des événements fracturaires et l'instauration d'un traitement s'est faite par l'envoi aux patientes et à leurs médecins traitants d'un questionnaire structuré. Dans cette étude, le but primaire est de décrire les attitudes médicales de prévention secondaire, le but secondaire d'analyser les motifs dé décision thérapeutique (type de fracture, antécédents de fractures), alors que le but tertiaire cherche à caractériser les femmes non traitées. Résultats, discussion : 7354 femmes ont été incluses dans cette étude, 183 dans le groupe fracture et 7171 dans le groupe contrôle. Le suivi moyen a été de 21 mois. L'introduction d'un traitement est restée rare dans chaque catégorie de fracture et a été plus importante pour le sous-groupe avec fracture vertébrale (p<0.001). La seule donnée associée à l'adjonction d'un traitement a été la présence d'un antécédent anamnestique de fracture vertébrale. La description des attitudes thérapeutiques après une fracture de fragilité, a montré que. 44 % des femmes ne reçoivent aucun traitement en prévention secondaire. Seule la fracture vertébrale et les antécédents de fracture vertébrale entraînent une modification de l'attitude thérapeutique des médecins traitants mais de façon encore insuffisante puisque plus de 50 % des femmes avec une fracture de vertèbre n'ont aucun changement dans leur prise en charge. Les femmes non traitées ne différaient pas des autres sur un plan socio-démographique. Le nombre de patientes dans chaque sous-groupe est relativement faible ce qui limite !a puissance statistique de l'analyse. Les données consistent essentiellement en du « selfreporting » ce qui peut limiter la signification de celles-ci. Les résultats sont cependant suffisamment inquiétants pour que de nouvelles campagnes d'information soient lancées auprès des médecins de .premiers recours quant à la nécessité d'instaurer un traitement efficace lors de la survenue d'une fracture clinique ou radiologique chez une femme en post-ménopause.

Schwann cell strip for peripheral nerve repair.

Many strategies have been investigated to provide an ideal substitute to treat a nerve gap injury. Initially, silicone conduits were used and more recently conduits fabricated from natural materials such as poly-3-hydroxybutyrate (PHB) showed good results but still have their limitations. Surgically, a new concept optimising harvested autologous nerve graft has been introduced as the single fascicle method. It has been shown that a single fascicle repair of nerve grafting is successful. We investigated a new approach using a PHB strip seeded with Schwann cells to mimic a small nerve fascicle. Schwann cells were attached to the PHB strip using diluted fibrin glue and used to bridge a 10-mm sciatic nerve gap in rats. Comparison was made with a group using conventional PHB conduit tubes filled with Schwann cells and fibrin glue. After 2 weeks, the nerve samples were harvested and investigated for axonal and Schwann cell markers. PGP9.5 immunohistochemistry showed a superior nerve regeneration distance in the PHB strip group versus the PHB tube group (> 10 mm, crossed versus 3.17+/- 0.32 mm respectively, P<0.05) as well as superior Schwann cell intrusion (S100 staining) from proximal (> 10 mm, crossed versus 3.40+/- 0.36 mm, P<0.01) and distal (> 10 mm, crossed versus 2.91+/- 0.31 mm, P<0.001) ends. These findings suggest a significant advantage of a strip in rapidly connecting a nerve gap lesion and imply that single fascicle nerve grafting is advantageous for nerve repair in rats.

Evidence for middle Cretaceous accretion at Santa Elena Peninsula (Santa Rosa Accretionary Complex), Costa Rica

An oceanic assemblage of alkaline basalts, radiolarites and polymictic breccias forms the tectonic substratum of the Santa Elena Nappe, which is constituted by extensive outcrops of ultramafic and mafic rocks of the Santa Elena Peninsula (NW Costa Rica). The undulating basal contact of this nappe defines several half-windows along the south shores of the Santa Elena Peninsula. Lithologically it is constituted by vesicular pillowed and massive alkaline basaltic flows, alkaline sills, ribbon-bedded and knobby radiolarites, muddy tuffaceous and detrital turbidites, debris flows and polymictic breccias and megabreccias. Sediments and basalt flows show predominant subvertical dips and occur in packages separated by roughly bed-parallel thrust planes. Individual packages reveal a coherent internal stratigraphy that records younging to the east in all packages and shows rapid coarsening upwards of the detrital facies. Alkaline basalt flows, pillow breccias and sills within radiolarite successions are genetically related to a mid-Cretaceous submarine seamount. Detrital sedimentary facies range form distal turbidites to proximal debris flows and culminate in megabreccias related to collapse and mass wasting in an accretionary prism. According to radiolarian dating, bedded radiolarites and soft-sediment- deformed clasts in the megabreccias formed in a short, late Aptian to Cenomanian time interval. Middle Jurassic to Lower Cretaceous radiolarian ages are found in clasts and blocks reworked from an older oceanic basement. We conclude that the oceanic assemblage beneath the Santa Elena Nappe does not represent a continuous stratigraphic succession. It is a pile of individual thrust sheets constituting an accretionary sequence, where intrusion and extrusion of alkaline basalts, sedimentation of radiolarites, turbidites and trench fill chaotic sediments occurred during the Aptian-Cenomanian. These thrust sheets formed shortly before the off-scraping and accretion of the complex. Here we define the Santa Rosa Accretionary Complex and propose a new hypothesis not considered in former interpretations. This hypothesis would be the basis for further research.

CT angiography helps to differentiate acute from chronic carotid occlusion: "carotid ring sign".

INTRODUCTION: Currently, there is no reliable method to differentiate acute from chronic carotid occlusion. We propose a novel CTA-based method to differentiate acute from chronic carotid occlusions that could potentially aid clinical management of patients. METHODS: We examined 72 patients with 89 spontaneously occluded extracranial internal carotids with CT angiography (CTA). All occlusions were confirmed by another imaging modality and classified as acute (imaging <1 week of presumed occlusion) orchronic (imaging >4 weeks), based on circumstantial clinical and radiological evidence. A neuroradiologist and a neurologist blinded to clinical information determined the site of occlusion on axial sections of CTA. They also looked for (a) hypodensity in the carotid artery (thrombus), (b) contrast within the carotid wall (vasa vasorum), (c) the site of the occluded carotid, and (d) the "carotid ring sign" (defined as presence of a and/or b). RESULTS: Of 89 occluded carotids, 24 were excluded because of insufficient circumstantial evidence to determine timing of occlusion, 4 because of insufficient image quality, and 3 because of subacute timing of occlusion. Among the remaining 45 acute and 13 chronic occlusions, inter-rater agreement (kappa) for the site of proximal occlusion was 0.88, 0.45 for distal occlusion, 0.78 for luminal hypodensity, 0.82 for wall contrast, and 0.90 for carotid ring sign. The carotid ring sign had 88.9% sensitivity, 69.2% specificity, and 84.5% accuracy to diagnose acute occlusion. CONCLUSION: The carotid ring sign helps to differentiate acute from chronic carotid occlusion. If further confirmed, this information may be helpful in studying ischemic symptoms and selecting treatment strategies in patients with carotid occlusions.