Aneurysmal growth in type-B aortic dissection: assessing the impact of patient-specific inlet conditions on key haemodynamic indices.

Type-B aortic dissection is a cardiovascular disease in which a tear develops in the intimal layer of the descending aorta, allowing pressurized blood to delaminate the layers of the vessel wall. In medically managed patients, long-term aneurysmal dilatation of the false lumen (FL) is considered virtually inevitable and is associated with poorer disease outcomes. While the pathophysiological mechanisms driving FL dilatation are not yet understood, haemodynamic factors are believed to play a key role. Computational fluid dynamics (CFD) and 4D-flow MRI (4DMR) analyses have revealed correlations between flow helicity, oscillatory wall shear stress and aneurysmal dilatation of the FL. In this study, we compare CFD simulations using a patient-specific, three-dimensional, three-component inlet velocity profile (4D IVP) extracted from 4DMR data against simulations with flow rate-matched uniform and axial velocity profiles that remain widely used in the absence of 4DMR. We also evaluate the influence of measurement errors in 4DMR data by scaling the 4D IVP to the degree of imaging error detected in prior studies. We observe that oscillatory shear and helicity are highly sensitive to inlet velocity distribution and flow volume throughout the FL and conclude that the choice of IVP may greatly affect the future clinical value of simulations.

The Influence of Minor Aortic Branches in Patient-Specific Flow Simulations of Type-B Aortic Dissection.

Type-B aortic dissection (TBAD) is a disease in which a tear develops in the intimal layer of the descending aorta forming a true lumen and false lumen (FL). Because disease outcomes are thought to be influenced by haemodynamic quantities such as pressure and wall shear stress (WSS), their analysis via numerical simulations may provide valuable clinical insights. Major aortic branches are routinely included in simulations but minor branches are virtually always neglected, despite being implicated in TBAD progression and the development of complications. As minor branches are estimated to carry about 7-21% of cardiac output, neglecting them may affect simulation accuracy. We present the first simulation of TBAD with all pairs of intercostal, subcostal and lumbar arteries, using 4D-flow MRI (4DMR) to inform patient-specific boundary conditions. Compared to an equivalent case without minor branches, their inclusion improved agreement with 4DMR velocities, reduced time-averaged WSS (TAWSS) and transmural pressure and elevated oscillatory shear in regions where FL dilatation and calcification were observed in vivo. Minor branch inclusion resulted in differences of 60-75% in these metrics of potential clinical relevance, indicating a need to account for minor branch flow loss if simulation accuracy is sought.

[Diagnostics and treatment of traumatic aortic injuries]. / Diagnostik und Therapie traumatischer Aortenverletzungen.

BACKGROUND: Traumatic aortic injuries (TAI) are rare injuries in blunt thoracic trauma, which have a high morbidity and mortality. Rapid and accurate diagnosis as well as the correct choice of treatment are elementary for patient survival. OBJECTIVE: Determination of the current standards for diagnostics of TAI in the acute trauma setting and evaluation of the current guidelines for treatment. MATERIAL AND METHODS: A literature search was carried out for articles describing diagnostics of TAI. Furthermore, the guidelines for treatment and follow-up of TAI were summarized. RESULTS: Despite the low specificity conventional chest X­ray is still named in the literature as initial diagnostic procedure. Primarily, computed tomography (CT) should follow as the method of choice for diagnostics and treatment stratification due to the high sensitivity and specificity. Thoracic endovascular aortic repair (TEVAR) is recommended by all guidelines as first line treatment of higher grades of TAI (grades II-IV) and has replaced open surgery in most cases. CONCLUSION: After rapid diagnosis and classification of TAI with CT, in most cases TEVAR has become the preferred treatment over open surgery.

Correction to: Perfusion MRI in CNS disease: current concepts.

The above article was published with one author name being incorrect. The published paper states "H. von Tengg", whereas it should be "H. von Tengg-Kobligk". The author name has been corrected above.

Hemodynamic Characterization of Peripheral Arterio-venous Malformations.

Peripheral arterio-venous malformations (pAVMs) are congenital vascular anomalies that require treatment, due to their severe clinical consequences. The complexity of lesions often leads to misdiagnosis and ill-planned treatments. To improve disease management, we developed a computational model to quantify the hemodynamic effects of key angioarchitectural features of pAVMs. Hemodynamic results were used to predict the transport of contrast agent (CA), which allowed us to compare our findings to digital subtraction angiography (DSA) recordings of patients. The model is based on typical pAVM morphologies and a generic vessel network that represents realistic vascular feeding and draining components related to lesions. A lumped-parameter description of the vessel network was employed to compute blood pressure and flow rates. CA-transport was determined by coupling the model to a 1D advection-diffusion equation. Results show that the extent of hemodynamic effects of pAVMs, such as arterial steal and venous hypertension, strongly depends on the lesion type and its vascular architecture. Dimensions of shunting vessels strongly influence hemodynamic parameters. Our results underline the importance of the dynamics of CA-transport in diagnostic DSA images. In this context, we identified a set of temporal CA-transport parameters, which are indicative of the presence and specific morphology of pAVMs.

Morphologic predictors of aortic expansion in chronic type B aortic dissection.

AIM: To identify morphologic factors affecting aortic expansion in patients with uncomplicated type B aortic dissections. METHODS: Computed tomography data of 24 patients (18 male; median age: 61 years), diagnosed with acute uncomplicated type B aortic dissections between 2002 and 2013, were retrospectively reviewed. All patients had at least two computed tomography angiography scans and six months of uneventful follow-up. Computed tomography scans were assessed by two independent readers with regard to presence and number of entry tears. Thoracic and abdominal aortic diameters were derived using image processing software. RESULTS: Twenty-two of 24 patients showed aortic expansion over a median computed tomography angiographic follow-up of 33.2 months. Annual rates showed an increase of 1.7 mm for total aortic diameter, 2.1 mm for the false and a decrease of -0.4 mm for the true lumen. In three patients (12.5%), aortic diameter exceeded 60 mm during follow-up, and all three patients underwent thoracic endovascular aortic repair. Patients with a maximum aortic diameter <4 cm at baseline showed a significantly higher expansion rate compared to cases with an initial maximum aortic diameter of ≥4 cm (p=0.0471). A median of two entries (range: 1-5) was recognized per patient. Presence of more than two entry tears (n = 13) was associated with faster overall diameter expansion (mean annual rates: 2.18 mm vs. 1.16 mm; p = 0.4556), and decrease of the cross-sectional surface of the true lumen over time (annual rate for > 2 entries vs. ≤2 entries: -7.8 mm2 vs. +37.5 mm2; p = 0.0369). Median size of entry tears was 12 mm (range: 2-53 mm). CONCLUSIONS: The results presented herein suggest that uncomplicated type B aortic dissection patients with more than two entry tears and/or an initial maximum aortic diameter of<4 cm are at risk for aortic dilatation and, therefore, may require stricter follow-up including the possible need for early intervention.

Comparison of morphological and rheological conditions between conventional and eversion carotid endarterectomy using computational fluid dynamics--a pilot study.

PURPOSE: To compare postoperative morphological and rheological conditions after eversion carotid endarterectomy versus conventional carotid endarterectomy using computational fluid dynamics. BASIC METHODS: Hemodynamic metrics (velocity, wall shear stress, time-averaged wall shear stress and temporal gradient wall shear stress) in the carotid arteries were simulated in one patient after conventional carotid endarterectomy and one patient after eversion carotid endarterectomy by computational fluid dynamics analysis based on patient specific data. PRINCIPAL FINDINGS: Systolic peak of the eversion carotid endarterectomy model showed a gradually decreased pressure along the stream path, the conventional carotid endarterectomy model revealed high pressure (about 180 Pa) at the carotid bulb. Regions of low wall shear stress in the conventional carotid endarterectomy model were much larger than that in the eversion carotid endarterectomy model and with lower time-averaged wall shear stress values (conventional carotid endarterectomy: 0.03-5.46 Pa vs. eversion carotid endarterectomy: 0.12-5.22 Pa). CONCLUSIONS: Computational fluid dynamics after conventional carotid endarterectomy and eversion carotid endarterectomy disclosed differences in hemodynamic patterns. Larger studies are necessary to assess whether these differences are consistent and might explain different rates of restenosis in both techniques.

Finite element analysis in asymptomatic, symptomatic, and ruptured abdominal aortic aneurysms: in search of new rupture risk predictors.

OBJECTIVES: To compare biomechanical rupture risk parameters of asymptomatic, symptomatic and ruptured abdominal aortic aneurysms (AAA) using finite element analysis (FEA). STUDY DESIGN: Retrospective biomechanical single center analysis of asymptomatic, symptomatic, and ruptured AAAs. Comparison of biomechanical parameters from FEA. MATERIALS AND METHODS: From 2011 to 2013 computed tomography angiography (CTA) data from 30 asymptomatic, 15 symptomatic, and 15 ruptured AAAs were collected consecutively. FEA was performed according to the successive steps of AAA vessel reconstruction, segmentation and finite element computation. Biomechanical parameters Peak Wall Rupture Risk Index (PWRI), Peak Wall Stress (PWS), and Rupture Risk Equivalent Diameter (RRED) were compared among the three subgroups. RESULTS: PWRI differentiated between asymptomatic and symptomatic AAAs (p < .0004) better than PWS (p < .1453). PWRI-dependent RRED was higher in the symptomatic subgroup compared with the asymptomatic subgroup (p < .0004). Maximum AAA external diameters were comparable between the two groups (p < .1355). Ruptured AAAs showed the highest values for external diameter, total intraluminal thrombus volume, PWS, RRED, and PWRI compared with asymptomatic and symptomatic AAAs. In contrast with symptomatic and ruptured AAAs, none of the asymptomatic patients had a PWRI value >1.0. This threshold value might identify patients at imminent risk of rupture. CONCLUSIONS: From different FEA derived parameters, PWRI distinguishes most precisely between asymptomatic and symptomatic AAAs. If elevated, this value may represent a negative prognostic factor for asymptomatic AAAs.

State-of-the-art of imaging detecting endoleaks post-EVAR with special focus on low-flow endoleaks.

Endovascular aortic repair (EVAR) necessitates lifelong surveillance for the patient, in order to detect complications timely. Endoleaks (ELs) are among the most common complications of EVAR. Especially type II ELs can have a very unpredictable clinical course and this can range from spontaneous sealing to aortic rupture. Subgroups of this type of EL need to be identified in order to make a proper risk stratification. Aim of this review is to describe the existing imaging techniques, including their advantages and disadvantages in the context of post-EVAR surveillance with a particular emphasis on low-flow ELs. Low flow ELs cause pressurization of the aortic aneurysm sac with a low velocity filling, leading to difficulty of detection by routine imaging protocols for EVAR surveillance, e.g. bi- or triphasic multislice computed tomographic angiography, magnetic resonance imaging and contrast enhanced ultrasound. In this article, we review the imaging possibilities of ELs and discuss the different imaging strategies available for depicting low flow ELs.

Accuracy and variability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR.

OBJECTIVES: This study aims to test whether inter-observer variability and time of diameter measurements for thoracic endovascular aortic repair (TEVAR) are improved by semiautomatic centerline analysis compared to manual assessment. METHODS: Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 males) were retrospectively analysed by two blinded experts in vascular radiology. Maximum aortic diameters at three positions relevant to TEVAR were assessed (P1, distal to left common carotid artery; P2, distal to left subclavian artery; and P3, proximal to coeliac trunk) using three measurement techniques: manual axial slices (axial), manual double-oblique multiplanar reformations (MPRs) and semiautomatic centerline analysis. RESULTS: Diameter measurements by both centerline analysis and the axial technique did not significantly differ from MPR (p = 0.17 and p = 0.37). Total deviation index for 0.9 was for P1 2.7 mm (axial), 3.7 mm (MPR), 1.8 mm (centerline); for P2 2.0 mm (axial), 3.6 mm (MPR), 1.8 mm (centerline); and for P3 3.0 mm (axial), 3.5 mm (MPR), 2.5 mm (centerline). Measurement time using centerline analysis was significantly shorter than for assessment by MPR. CONCLUSIONS: Centerline analysis provides the least variable and fast diameter measurements in TEVAR patients with the same accuracy as the current reference standard MPR.

Technical aspects of EVAR for infrarenal AAA.

Technical aspects are crucial for planning and performing successful endovascular repair of abdominal aortic aneurysms (AAA). Planning should be based on high-quality computed tomography angiography scans with a slice thickness of ≤ 1 mm. However, even without a workstation for image postprocessing, important angle estimations can be easily performed. Several devices are available today to treat abdominal aneurysms. In most elective cases all currently available 3rd generation devices perform comparably if minimal requirements are kept in mind. A safe and technically precise implantation requires cooperation with the involved anesthesiologist in order to manage anticoagulation, blood pressure regulation in general and in currently evolving regional anesthesia. Modern endograft implantation involves highly technical resources, for example guide wires or catheters. Beside patient selection, an optimal procedure planning, graft model choice and endovascular skills are mandatory aspects. In the near future, further improvements in device design and deployment mechanism will allow better device alignment, paving the way for an even broader application of endovascular aneurysm repair (EVAR).

Reliability of semiautomatic centerline analysis versus manual aortic measurement techniques for TEVAR among non-experts.

OBJECTIVES: The study aimed to test whether reliability and inter-observer variability of preoperative measurements for thoracic endovascular aortic repair (TEVAR) among non-experts are improved by semiautomatic centerline analysis compared with manual assessment. METHODS: Preoperative computed tomography (CT) angiographies of 30 patients with thoracic aortic disease (mean age 66.8 ± 11.6 years, 23 men) were retrospectively analysed in randomised order by one blinded vascular expert (reference standard) and three blinded non-expert readers. Aortic diameters were measured at four positions relevant to TEVAR using three measurement techniques (manual axial slices, manual multiplanar reformations (MPRs) and semiautomatic centerline analysis). Length measurements were performed using centerline analysis. Reliability was calculated as absolute measurement deviation (AMD) from reference standard and inter-observer variability as coefficient of variance (CV) among non-expert readers. RESULTS: For axial, MPR and centerline techniques, mean AMD was 7.3 ± 7.7%, 6.7 ± 4.5% and 4.7 ± 4.8% and mean CV was 5.2 ± 4.2%, 5.8 ± 4.8% and 3.9 ± 5.4%. Both AMD and CV were significantly lower for centerline analysis compared with axial technique (p = 0.001/0.042) and MPR (p = 0.009/0.003). AMD and CV for length measurements by centerline analysis were 3.2 ± 2.8% and 2.6 ± 2.4%, respectively. Centerline analysis was significantly faster than MPR (p < 0.001). CONCLUSIONS: Semiautomatic centerline analysis provides the most reliable and least variable diameter and length measurements among non-experts in candidates for TEVAR.

[Vascular surgery in the elderly - recommendations for clinical practice]. / Gefäßchirurgie im Alter - Handlungsempfehlungen für die chirurgische Praxis.

Due to the increasingly aging populations of the industrialised countries, the prevalence of vascular disorders is increasing, with an emerging patient subgroup of 80  years and older (octogenarians), often multi-morbid with an increased risk of anaesthesiological and surgical complications. This review article presents evidence-based indications for vascular surgery in the elderly (> 80  years), and the influence of advanced age on surgical results. Guidelines for daily practice were drawn from a thorough analysis of current treatment recommendations for three vascular disorders (carotid artery stenosis, abdominal aortic aneurysm, and peripheral arterial disease) with the aim of assisting the primary care physician in deciding upon the therapeutic management. In summary, evidence indicates that CEA (carotid endarterectomy) is the gold standard therapy for carotid artery stenosis, as opposed to the "best medical treatment" and CAS (carotid artery stenting). With suitable morphology of the aneurysm, endovascular aneurysm repair (EVAR) is the therapy of choice for abdominal aortic aneurysm (AAA). In elderly patients unfit for open repair and with a life expectancy of less than 4  years, EVAR does not offer any survival benefit compared with no intervention. In such patients, conservative therapy should be taken into consideration. Due to the significantly reduced life expectancy after a major amputation, the value of infrainguinal revascularisation is high, with the exception of patients aged > 90  years.

Semi-automated volumetric analysis of lymph node metastases during follow-up--initial results.

OBJECTIVE: Quantification of tumour burden in oncology requires accurate and reproducible evaluation. The current standard is RECIST measurement with its inherent disadvantages. Volumetric analysis is an alternative for therapy monitoring. The aim of this study was to evaluate the feasibility of volumetric analysis of lymph node metastases using a software prototype in a follow-up setting. METHODS: MSCT was performed in 50 patients covering the chest, abdomen and pelvis. A total of 174 suspicious lymph nodes were evaluated by two radiologists regarding short axis diameters and volumetric analysis using semi-automated software. Quality of segmentation, time, maximum diameter and volume were documented. Variability of the derived change rates was computed as the standard deviation of the difference of the obtained respective change rates. RESULTS: The software performance provides robust volumetric analysis. Quality of segmentation was rated acceptable to excellent in 76-79% by each reader. Mean time spent per lesion was 38 s. The variability of change in effective diameters was 10.6%; for change rates of RECIST maximum diameter variability was 27.5%. CONCLUSION: Semi-automated volumetric analysis allows fast and convenient segmentation of most lymph node metastases. Compared with RECIST the inter-observer-variability in baseline and follow-up is reduced. This should principally allow subtle changes to be subclassified within the RECIST stable range as minor response [-15% to +10%].

3D printing based on imaging data: review of medical applications.

PURPOSE: Generation of graspable three-dimensional objects applied for surgical planning, prosthetics and related applications using 3D printing or rapid prototyping is summarized and evaluated. MATERIALS AND METHODS: Graspable 3D objects overcome the limitations of 3D visualizations which can only be displayed on flat screens. 3D objects can be produced based on CT or MRI volumetric medical images. Using dedicated post-processing algorithms, a spatial model can be extracted from image data sets and exported to machine-readable data. That spatial model data is utilized by special printers for generating the final rapid prototype model. RESULTS: Patient-clinician interaction, surgical training, medical research and education may require graspable 3D objects. The limitations of rapid prototyping include cost and complexity, as well as the need for specialized equipment and consumables such as photoresist resins. CONCLUSIONS: Medical application of rapid prototyping is feasible for specialized surgical planning and prosthetics applications and has significant potential for development of new medical applications.

Treatment of an asymptomatic penetrating aortic ulcer in a young patient.

We want to report and discuss the indication for open surgery for an asymptomatic penetrating aortic ulcer (PAU) in the era of thoracic endovascular aortic repair (TEVAR). A 31-year-old female presented with the diagnosis of an aneurysm in the distal aortic arch. With respect to the patients young age, the controversial status of connective tissue disorders and in the absence of concomitant disease, open repair was indicated. There was no proof of a mycotic plaque or connective tissue disease in the microbiological-, pathological analysis and at electron-microscopy. The patient was discharged on the thirteenth postoperative day. In spite of good preliminary results of TEVAR in PAU, in selective cases there is still an indication for open surgery.

Comparison of diagnostic quality and accuracy in color-coded versus gray-scale DCE-MR imaging display.

PURPOSE: The purpose of this study was to evaluate the diagnostic value and tumor-vascular display properties (microcirculation) of two different functional MRI post-processing and display (color and gray-scale display) techniques used in oncology. MATERIALS AND METHODS: The study protocol was approved by the IRB and written informed consent was obtained from all patients. 38 dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) data sets of patients with malignant pleural-mesothelioma were acquired and post-processed. DCE-MRI was performed at 1.5 tesla with a T1-weighted 2D gradient-echo-sequence (TR 7.0 ms, TE 3.9 ms, 15 axial slices, 22 sequential repetitions), prior and during chemotherapy. Subtracting first image of contrast-enhanced-dynamic series from the last, produced gray-scale images. Color images were produced using a pharmacokinetic two-compartment model. Eight raters, blinded to diagnosis, by visual assessment of post-processed images evaluated both diagnostic quality of the images and vasculature of the tumor using a rating scale ranging from -5 to +5. The scores for vasculature were assessed by correlating with the maximum amplitude of the total-tumor-ROI for accuracy. RESULTS: Color coded images were rated as significantly higher in diagnostic quality and tumor vascular score than gray-scale images (p < 0.001, 0.005). ROI signal amplitude analysis and vascular ratings on color coded images were better correlated compared to gray-scale images rating (p < 0.05). CONCLUSION: Color coded images were shown to have higher diagnostic quality and accuracy with respect to tumor vasculature in DCE-MRI, therefore their implementation in clinical assessment and follow-up should be considered for wider application.

Hybrid approach for arch and thoracoabdominal pathologies.

The endovascular era began about 20 years ago and subsequently revolutionized vascular surgery as a less invasive treatment option, especially for high risk patients. In the late 1990s, a new hybrid approach for arch and thoracoabdominal pathologies was developed. Debranching and rerouting supra-aortic and visceral aortic branches with extra-anatomic bypass grafting was performed in order to achieve sufficient landing zones demanding for subsequent stent grafting. The initial single-center results of small series up to 20 patients were encouraging with acceptable complication rates. Hybrid arch procedures are feasible but seem to carry risks. However, the latest reports for thoracoabdominal hybrid procedures demand a word of caution due to high morbidity rates. The hybrid approach may be reserved for a selected comorbid patient cohort, which is regarded unfit for open reconstruction.

Paraplegia after spontaneous dissection of the abdominal aorta.

We report a case with spinal cord ischemia and consecutive paraplegia following spontaneous isolated abdominal aortic dissection (IAAD). A 63-year-old female was admitted to the surgical emergency room with severe lumbar back pain and accompanying paresthesia of both legs. Contrast enhanced computed tomograpy (CT) of the abdomen showed an infrarenal IAAD in a normal size aorta with patent lumbar arteries. It was assumed that a surgical or interventional approach would not be helpful to improve spinal cord perfusion. Therefore, non operative therapy consisted of lowering blood pressure to prevent further dissection. The patient developed an anterior spinal artery syndrome with permanent paraplegia. Thus, blood pressure was raised for optimal spinal cord perfusion. To lower the spinal pressure, cerebrospinal fluid drainage was attempted. A three month follow-up CT scan showed spontaneous remodelling of the aorta. The neurological deficit persisted. IAAD is a rare differential diagnosis of lumbar back pain and can be associated with paraplegia as the leading symptom. Individualized treatment is indicated. Surgical treatment options concerning paraplegia are limited.