The Future of Continuing Education in Diagnostic Imaging

Common Pathology & Imaging of the Aorta

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Authors: Karen Vieira, PhD, MSM & Deirdre O'Donnell, M.Sc.

Abstract: Aortic pathologies are relatively rare compared to other cardiovascular events such as myocardial infarctions; however, they may be fatal to patients affected by them unless treated without delay. Damage to the aorta may be a result of trauma or other risk factors. Imaging is an effective tool in the detection of aortic pathology, and the initial assessment of its severity. This information may inform the type of treatment appropriate for the individual patient. Following the administration of therapy, these patients require regular monitoring and assessment. Imaging is also often a main component of this long-term follow-up. Techniques associated with the visualization of aortic pathology include MRI, CT and ultrasound. In addition, some forms of molecular and functional imaging may have potential in the assessment of aortic disease. This article will describe some examples of aortic pathology and how the analyses of different imaging techniques result in their quantification and visualization.

 

 Introduction

 

The aorta is a primary blood vessel in the human cardiovascular system. It begins at the left ventricle and proceeds downward through the thorax and abdomen [1]. Its main function is to be the main trunk of a branching arterial system that delivers blood to many organs and tissues [1]. The aorta is a valuable reference point for many other structures and their anomalies (see '[Common Pathology & Imaging of the Chest]'). However, the aorta is also subject to a range of its own pathologies and abnormalities. The accurate and timely diagnosis of aortic pathology is often vital, as it may be fatal in many cases [2]. When not immediately life-threatening, conditions affecting the integrity or function of the aorta may still require consistent monitoring. This assesses the risk and incidence of sudden deterioration or other effects on the mortality of the patient.

 

 

Illustration of Aorta

Fig.1 . The aorta is a wide vessel, looping above the heart to form the ascending aorta, and then behind and below it to form the descending aorta. Many important arteries (labeled) branch out from it. Courtesy: Edoarado - Own work based on: Arterial System en.svg, Coronary arteries.svg.. Licensed under CC BY-SA 3.0 via Wikimedia Commons - https://commons.wikimedia.org/wiki/File:Aorta_scheme_en.svg#/media/File:Aorta_scheme_en.svg

 

Aortic dysfunction and damage is relatively rare compared to other, better-known cardiovascular conditions and adverse events such as stroke. Strokes (or ischemic damage to the brain or heart) affect up to 294 people per 100,000 every year, whereas aortic dissection (an example of the pathology to be discussed below) is estimated to affect a maximum of 3.5 people per 100,000 every year [3, 4]. The detection of aortic pathology depends heavily on imaging. Symptoms associated with these disorders are often widespread pain or discomfort, which may be mistaken by the patient for other possibilities such as cramp, or even be ignored due to their often chronic and low-lying nature. More serious and obtrusive symptoms may be mis-attributed to disorders of the nervous system or other parts of the cardiovascular system. Damage to the aorta is often quite patent when analyzed through imaging, due to its relatively he dimensions of this vessel vary according to age and gender [1]. However, the average total diameter of the ascending aorta has been found to be approximately 33mm and 36mm for adult women and men respectively [1]. Examples of anomalies that can be detected by diagnostic imaging may include intimal flaps or tears, subadventitial tears and transections. These are normally related to trauma.

 

Other forms of pathology, which will be discussed here in more detail, may be related to progressive cardiovascular diseases or to adverse events with a more abrupt onset. The diagnosis of aortic pathology is enhanced using techniques that can visualize or otherwise quantify damage to this vessel. Historically, conventional angiography has been the 'go-to' technique in these pursuits. However, this modality has been overtaken in recent years by developments in several forms of imaging [2]. Many of these techniques may effectively demonstrate aortic shape and size, and the differences from the anatomical norm that may indicate a pathology and/or underlying condition [5]. Imaging may also effectively facilitate the often exhaustive planning and long-term follow-up involved in the treatment of aortic pathology [6]. Some patients affected by aortic pathology, who have undergone surgical treatment for this, require regular monitoring for the rest of their lives [7]. Therefore, the relevance of imaging techniques to aortic pathology extends far beyond diagnosis. Imaging in terms of both initial and routine assessment of the aorta will be discussed here.

 

 

Imaging Modalities/Techniques & Their Applications in Aortic Imaging

 

Conventional Chest X-Ray (CXR)

 

This modality is well-established and may be regarded as out-moded compared to other techniques; however, it is useful for the routine and first-line assessment of structures found in the thoracic cavity, which may include the aorta. CXR, which may also be known as 'plain X-ray' or 'plain radiography' is often indicated in the pre- and post-operative assessment of aortic aneurysms [8]. Plain X-rays may also be useful in the assessment of pathology located in the abdominal aorta [9]. However, it is often limited to offering information on the basic morphology of the aorta, and is considered to be much less sensitive to complications related to aneurysms (see below) compared to newer techniques such as CTA and US [9].

 

 

Computed Tomography (CT)

 

Computed tomography is a long-established imaging technique associated with many variations and developments that keep it at the forefront of diagnostic and routine imaging. This applies to the visualization of the aorta [6]. As with MRI, CT is combined with vessel-specific enhancement (or angiography) to give the technique of CT-angiography (CTA) [6]. CTA has largely replaced conventional digital subtraction angiography (DSA) and fluoroscopy in pre- and post-operative aortic imaging. On the other hand, fluoroscopy is still often used in the course of procedures such as stent placement, due to the familiarity of many surgeons with this modality [6]. CTA is often indicated in the standard initial assessment of patients receiving surgical treatment (see below) for an aneurysm [8]. Angiography may also be combined with more state-of-the-art forms of CT, such as multidetector CT (i.e. MDCTA) to generate detailed and specific two- and three-dimensional images [10]. Again, this is often indicated in the ongoing evaluation of aortic aneurysms and their response to surgical intervention [10].

 

Despite its popularity, CTA is associated with some disadvantages. This includes the increased exposure to radiation over time and the nephrotoxicity of the contrast material used in CT [5]. Some researchers assert that the cumulative exposure associated with repeated CT procedures significantly affect the probability of cancer development [9]. However, newer variations of CT, such as dual-energy CT, may reduce radiation exposure, and the need for contrast, if applied to aortic imaging [5]. On the other hand, long-term follow-up CT studies are associated with increased cost [9]. As patients with a history of surgical aneurysm repair (see below) require lifelong assessment through imaging in cases of complications, these are valid considerations when selecting techniques for this [4].

 

 

Magnetic Resonance Imaging (MRI)

 

MRI is often used in the evaluation of aortic pathology. This is often combined with the injection of contrast material into the cardiovascular system, which is known as MR-angiography or MRA. MRA is often indicated when assessing suspected aortic pathology, and in the long-term follow-up of patients for whom conservative therapies are recommended [6]. However, the use of MRI can be time-consuming in comparison to other standard techniques, particularly ultrasound (see below) [6]. Obviously, MRI is also unsuitable for patients with metal debris, implants or other objects located within the chest or abdomen.

 

Positron Emission Tomography (PET)

PET is a technique that can generate highly sensitive, specific images through the detection of radiation. This is generated by tracer isotopes, which are designed to bind to molecules, cell fragments or even full cells relevant to the pathology in question. In the case of aortic pathology, these are often 18F isotopes that bind to glucose to form 18F-deoxy-glucose (FDG). As glucose is present in high concentrations within the bloodstream, FDG-PET may offer well-detailed images of the aorta, and of aortic abnormalities. Some studies indicate that increased FDG uptake (and a concomitant increase in signal on PET-generated images) in the aorta is indicative of inflammation from disorders such as aneurysm formation [11]. 

Single Photon Emission Computerized Tomography (SPECT)

SPECT is a variation of CT that detects the emission of gamma rays from radioactive isotopes, which may be injected to bind target molecules as tracers in a manner similar to PET [12]. Alternatively, the tracers may be added to red blood cells (RBCs) taken from a patient, which are then injected to facilitate cardiovascular imaging [12]. Therefore, SPECT may be a viable alternative in the imaging of the aorta. RBCs labeled with [99m]-technetium (99mTc) has demonstrated some efficacy in detecting complications related to the treatment of aneurysms (see below) [13]. Other forms of SPECT tracer with potential in aortic imaging include vascular molecules such as 99mTc-annexin V, [111]-indium- (111In) bound platelets and 111In-bound leukocytes [12]. PET and SPECT-based techniques are also known as functional, nuclear or molecular imaging.

 

 

Ultrasound Technology

 

Ultrasound imaging of the aorta and its pathology is also known as transesophageal or transthoracic echocardiography [6]. This is a standard procedure in the diagnosis of aortic pathologies, and in the routine assessment of patients undergoing non-surgical treatments for these [6]. It may also be used in intraoperative imaging during procedures to surgically correct aortic damage or disease [6]. Echocardiography also often confers the advantage of reduced durations of imaging procedures, lower cost and more portable equipment. This is more amenable to the assessment of bed-ridden patients or patients recovering from surgery.

 

An additional form of ultrasound used in the imaging of aortic pathology is intravascular ultrasound. This is often used in the course of procedures such as endovascular aneurysm repair [5]. Duplex ultrasound (DUS) is also often used in the assessment of patients receiving this and similar procedures [5]. Contrast-enhanced US (CEUS), alone or in combination with DUS, is also emerging as a candidate to replace CTA in the assessment of pathologies such as aneurysms and their response to treatment [7, 9].

 

Common Pathologies of the Aorta

 

 

Aortic Aneurysm

 

This is a pathology that affects the integrity and functions of arterial walls, and may have a considerable impact on blood flow and the tissues supplied by the blood vessel in question. Aortic aneurysms are structural defects in the inner surface (or wall) of the vessel. An aneurysm may be visualized as a balloon-like bulge off to one side of the aorta, or as a mis-shapen lesion protruding from it. Blood may flow into the aneurysm rather than continue throughout the vessel. Aortic aneurysms may be associated with certain diseases, conditions and risk factors. Variations in many cellular and molecular factors, related to the elasticity of the inner aortic wall, are implicated in aneurysm development [12]. Some forms of trauma may also result in an aneurysm [14]. Aneurysms may form at any point along the aorta. Thoracic aortic aneurysms may be the least frequently-diagnosed type, reportedly affecting only 10 people per 100,000 per year [15]. Abdominal aneurysms are a more common occurrence, albeit only in certain age groups. Estimates suggest that they are present in approximately 7% of people over 65 years [16].  Common locations include the segment of the abdominal aorta below the kidneys and above the point of bifurcation into the iliac arteries [9]. These are known as infrarenal aneurysms.

 

Aortic aneurysms may be stable, or a less than immediate threat to the life of the patient. Alternatively, an aneurysm may rupture, or break at the weakened portion of the arterial wall. This may result in severe blood loss leading to shock, ischemia in many tissues and organs, nervous system damage, and fatality. This often requires immediate surgical intervention. The risk of rupture is affected by many factors and variables such as the elasticity, size and movement of the aneurysm relative to that of the rest of the aorta [17]. Ruptured abdominal aortic aneurysms may be related to as many as 15,000 deaths per year [12]. The risk of aneurysm development is affected by certain conditions, which are often genetic in nature [18]. Other factors that affect this risk include a history of smoking, advanced age and male gender [2]. Aneurysms may be associated with symptoms such as abdominal and back pain, but this typically only applies to lesions in the process of rupture, or at higher risk of this. This pathology may also be associated with inflammation, which may contribute to aortic wall weakness and eventual rupture [11].

 

 

Visualization of an Aortic Aneurysm

 

The detection of aortic aneurysms may be divided into two basic categories: direct visualization of the anomaly (as described above) using imaging techniques in combination with angiography, or through variations in the mechanical function (i.e. the muscular contractions that allow the normal 'pumping' action produced by the muscular layers of the vessel, which maintains blood flow from the heart) of the aorta. Under normal circumstances, movement along the aorta is highly uniform and forms consistent rhythms, waves or patterns which may be calculated, mapped and quantified. Variations in these are often associated with defects in the structure of arterial walls [12]. Therefore, changes in these mechanical properties are often indicative of an aneurysm. Motion or pulse variations are most often detected using various types of US [12]. Alternatively, PET may highlight aneurysms through increased signal at parts of the aortic wall through increased FDG uptake. This has been found to correlate with increases in inflammatory markers and reductions in the proteins that make up arterial walls (e.g. collagen) [11]. Aneurysms may also form as a rare complication of aortic valve replacement (see below) [19].

 

Generally, transesophageal echocardiography and MRA are regarded as having high specificity and sensitivity in both the diagnosis and assessment of patients with this pathology [6]. Other forms of US, such as doppler imaging, may effectively evaluate the risk of rupture before and after surgery to address this pathology (see below) [17, 20]. Doppler imaging may detect the presence of aneurysms through changes in aortic wall motion [12]. Another variation of conventional US known as pulse-wave imaging (PWI) may highlight the presence of an aneurysm through defects in aortic pulse-wave velocity [12]. The presence of an aneurysm is also related to extravasation (or leaking outward) of contrast material, as visualized by CEUS [12]. CT may generate 3D images through the analysis and processing of multiple sectional images [12]. Contrast-enhanced conventional CT allows for the accurate estimation of the diameter and interior volume (or lumen) of the aorta [12]. This is vital to evaluating the eligibility of the individual for certain surgical treatments (see below) [12]. Non-contrast enhanced CT may also be useful in the assessment of this pathology. This technique may distinguish blood flow within an aneurysm from other features such as calcification [21]. MRI is also effective in the direct detection of aneurysms (i.e. as bulges or defects in the aortic wall) [12]. This technique is also effective in detecting other signs of pathology, such as thrombi and interruptions to blood flow [22].

 


Figure 2. Contrast-enhanced CT showing a ruptured abdominal aortic aneurysm (AAA). Case courtesy of Dr Donna D'Souza, Radiopaedia.org. From the case rID: 3828.

 

Treatment of an Aortic Aneurysm

 

Some patients with stable aneurysms (or lesions that are asymptomatic and/or are at lower risks of rupture) may manage their condition with drug therapy such as beta-adrenergic receptor blockers and angiotensin suppressors [18]. Others may require corrective surgery, and even then patients must often undergo routine assessment afterward. This evaluates the risks and incidence of adverse events such as post-operative complications or treatment failure [5]. Procedures that correct this pathology are known as aneurysm repair. These are often open surgeries in which the aneurysm is corrected from outside the vessel [9]. Endovascular aneurysm repair (in which, as the name suggests, the anomaly is corrected from within the aorta) is a newer variation on this conventional surgery. This procedure involves the insertion of an artificial graft (an 'endograft') that is positioned in relation to the aneurysm in such a way that blood flow is diverted away from it and down through the aorta as normal. This graft is often attached to a stent, which may run the entire length of the aortic section in question (i.e. abdominal or thoracic) to reinforce the graft and hold it in place. In the case of abdominal aortic grafts, the stent may be designed so as to also extend into the iliac arteries, for additional structural integrity.

 

Endovascular repair is regarded as a radical advancement on traditional aneurysm correction, although it requires much more accurate visualization before and after surgery [5]. The function of this is to optimize patient eligibility, fully optimize the size and shape of a graft for the individual patient, and to enhance post-operative assessment. Fortunately, DUS, MRA and CTA offer effective and accurate graft imaging [5]. On the other hand, the follow-up assessment of endovascular aneurysm repair may be associated with increased risks of kidney damage and radiation exposure, due perhaps to the use of CT [9]. This is particularly important in evaluating the success of an aneurysm repair and the incidence of complications [9]. Endoleaks (in which blood persists in flowing into the aneurysm) and other complications (e.g. stent migration) may lead to repeat surgeries to repair or remove these devices. Meta-analysis has shown that DUS and CEUS are sensitive to endoleaks requiring correction, at rates of up to 77% and 98% respectively [9].

 

Plain X-ray techniques are regarded as much less efficient in the detection of endoleaks [9]. However, they may be more useful in the detection of stent migrations, as well as other complications, e.g. 'kinks' that may develop in stents [9]. Other forms of complications following repair include thrombus formation on or near the graft and graft failure [7]. On the other hand, a study including 90 patients who underwent an endovascular repair for infrarenal aneurysms found that a combination of conventional angiography, radiography and DUS had a sensitivity of 87.5% compared to 75% for DUS alone [8]. However, the specificity and negative predictive values of these two modalities were similar, although the positive predictive value of the combined modality was 65.6% compared to 87.5% for DUS [8]. CTA is regarded as the gold standard in the detection of endoleaks [23]. On the other hand, some studies indicate that conventional CT without contrast and MRI may be an adequate replacement for CTA in cases for which cumulative radiation exposure or kidney damage may be a concern [12]. MRA has been found to be comparable to CTA in sensitivity for endoleaks [22]. Other techniques that may detect endoleaks include SPECT and PET. A small-scale study (including 13 patients) suggested that the sensitivity of 99mTc-labeled RBC-enhanced SPECT to endoleaks was similar to that of CT [13]. Animal studies have demonstrated the potential of 99mTc-P-selectin in the visualization of aneurysms by SPECT [24].

 

 

Aortic Dissection

 

The rupture of the aortic wall, as described above, is also known as an aortic dissection. This may occur as the 'end-stage' of an aneurysm. However, dissections may also be associated with other risk factors, such as genetic predisposition (e.g. Marfan's syndrome and mutations in genes associated with transforming growth factor-beta (TGF-β) signaling pathways), inflammation and genetic factors that influence the risk of aneurysm formation [18]. Dissections may also be related to trauma in some cases [9]. They may appear as ruptures associated with an aneurysm, or as tears in the aorta. Some forms of dissection may be restricted to inner layers of the aorta, while the outer layers remain intact [25]. This forms a 'false lumen', which diverts blood flow into it at the expense of the original lumen [25]. The establishment of a false lumen increases the risk of other lesions similar to an aneurysm (a 'pseudoaneurysm') and a complete rupture of the aorta [25]. Aortic dissections are also associated with features similar to aneurysms (i.e. thrombi, calcification) and may also be associated with the development of hematoma [25].

 

 

 

A dissection with false lumen (arrows) and true lumen

Figure 3. An enhanced sagittal CT of an extensive aortic dissection. Case courtesy of Dr Muhammad Essam, Radiopaedia.org. From the case rID: 18033.

 

 

Visualization of an Aortic Dissection

 

The formation of dissections may be visualized in a similar manner to that of an aneurysm. They may be directly visible on MRA- or CTA-generated images, i.e. through changes or extravasations of contrast [25]. 'Partial' dissections typically create the impression that the diameter of the aorta has increased [25]. Therefore, coronal sections and/or 3D images generated by CT may efficiently highlight this sign of dissection [25]. It follows that forms of CT with an optimal z-axis resolution are the most suitable when generating images of a dissection. Many researchers regard conventional 64-slice tomography as superior in this, although the collimations may be smaller than those of 16-slice techniques [25]. Dual-energy CT and techniques that deliver more sections have the advantage of speed - 320-slice CT may generate a whole-aorta image in three seconds or less [25]. Dissections, as with aneurysms, may result in the formation of large clots due to blood pooling in a false lumen or pseudoaneurysm. This may give rise to a feature known as 'crescent sign', or the shape created by this thrombus and its effects on the contrast or attenuation immediately surrounding it [25].

 

 

 

 

CT showing a dissection of moderate severity (or grade 3) with pseudoaneurysm.

Figure 4. Axial CT showing a dissection of the ascending aorta. Courtesy: Voitle, E., W. Hofmann, and M. Cejna, Aortic emergencies-diagnosis and treatment: a pictorial review. Insights Imaging, 2015. 6(1): p. 17-32. Case courtesy of Dr David Cuete, Radiopaedia.org. From the case rID: 29247.

 

 

 

Treatment of an Aortic Dissection

 

 

Conventional therapy for aortic dissection is similar to that for patients with an aneurysm [18]. Extensive and/or traumatic dissections may also be corrected using stent-grafts [25]. Like stents intended for aneurysm repair, the shape and size of stents intended to repair dissection is determined by the site of dissection (e.g. dissections near the aortic arch may be curved to match this structure) and also by the distance of intact aortic tissue superior to the dissection and that inferior to it [25]. The eligibility for such an endovascular procedure may depend on risks related to the occlusion of a major artery, if its orifice is located near enough to the dissection. A surgeon may make a decision to prioritize one large artery over another. For example, he or she may sacrifice the patency (non-obstruction) of the left subclavian artery in favour of that of a vertebral artery [25].

 

DSA pseudoaneurysm dissection with stent/graft

Figure 5. CXR showing a thoracic aortic stent (arrows) implanted in the course of endovascular aortic repair. Case courtesy of Dr Ian Bickle, Radiopaedia.org. From the case rID: 30196.

 

 

Aortic Stenosis

 

Stenosis is a term referring to the narrowing of an artery, which results in reductions in lumen volume and thus the volume, velocity and frequency of blood flow. In the case of the aorta, stenosis is most often observed at the point of exit from the left ventricle. This leads to widespread reductions in the supply of oxygenated blood, resulting in ostentatious symptoms such as syncope (fainting), chest pain and breathing problems. Stenosis may occur due to the stiffening or thickening of the tissues of the aortic valve. This valve regulates blood flow out of the heart into the aorta, and normally exhibits a regular pumping motion to do so. Valve stiffening (through calcification) restricts the function of this structure, and may severely impact normal blood flow. Alternatively, the aorta may become narrowed just before or after it exits the valve [26]. This is associated with increased calcification of the aorta at these points [27]. Aortic stenosis may be accompanied by hypertrophy, or increased tissue growth, in the left ventricle [26]. Other signs of this pathology include the dilation of the ascending aorta [28]. The risk of aortic stenosis is influenced by advanced age (most cases are seen in patients of 80 or more years), genetic factors, pre-existing hypertension and diabetes, and lifestyle choices such as habitual smoking [27]. The presence of an aortic valve malformation, in which the valve is made up of two components (i.e.  bicuspid) rather than the usual three (tricuspid), is also associated with an increased risk of stenosis [27]. These are rare anomalies, but common compared to cases in which uni- or quadricuspid valves are present [28].

 

 

Visualization of Aortic Stenosis

 

Aortic stenosis is traditionally imaged using echocardiography. This technique is used to evaluate left ventricular mass [26]. However, this may result in false positives in cases for which left ventricular hypertrophy is not a factor [26]. On the other hand, patients without hypertrophy may exhibit increased ventricular wall thickness, which may also be detected using echocardiography [26]. Echocardiography also quantifies stenosis in terms of the 'dimensionless index' (DI), a ratio between the outflow tract velocity of the aortic valve and that of the left ventricle [29]. It is unclear which variable affecting this velocity most accurately reflects this index. A study including 70 patients receiving echocardiograms indicated that values for peak velocity significantly improved variation in DI compared to velocity-time-integral [29]. However, the authors concluded that this did not optimize noise on the ultrasound, or improve the detection of change in DI [29]. 2D- and 3D-ultrasound can also provide data such as valve size and dimensions, the 3D structure (and number) of valves, atrial size, ventricular ejection fraction and pressure gradients in the aorta and ventricle [30]. Variations in any of these factors may indicate aortic stenosis. MDCTA is also effective in the 2d and 3D imaging of aortic stenosis and the structural defects as described above [28]. MRA may also generate high-quality images based on volumetric and flow-velocity data [28]. Plain CXRs may demonstrate basic signs of stenosis, such as enlarged cardiac silhouette (indicated by increased contrast) [30].

 

MDCT-generated image of a normal tricuspid aortic valve in diastolic phase

Figure 6 (above). Contrast-enhanced CT of valvular aortic stenosis with pronounced calcification (arrow). Case courtesy of Dr Hani Al Salam, Radiopaedia.org. From the case rID: 14480.

 

 

Figure 7 (above). MRA of an aorta showing marked stenosis (arrow). Case courtesy of Dr Yune Kwong, Radiopaedia.org. From the case rID: 29895.

 

Treatment of Aortic Stenosis

 

Untreated aortic stenosis is associated with a two-year mortality rate of approximately 50% [27]. This may be addressed using a range of surgical techniques. These include aortic valve replacements (AVR) [31]. These procedures are associated with increased risks of residual left-ventricular hypertrophy, however, which is associated with poorer prognoses [31]. Variations on AVR include trans-catheter valve replacements or implantations, in which prosthetic valves are extended into the ventricle and placed in the correct location through a catheter [32]. This may reduce surgical invasion, and is indicated for patients for whom open surgery is unsuitable [33]. Transcatheter implantation is associated with complications such as aortic regurgitation [32]. This is the flow of blood back into the ventricle through the aorta. Information on the severity of regurgitation may be generated using US, which quantifies this in terms of the volume of regurgitated blood [32]. MRI of the heart has also shown potential in this, by quantifying changes in phase-contrast velocity [32]. Some patients may benefit from a more conservative form of treatment known as balloon valve dilation [27]. However, this procedure is associated with the risk of recurrent stenosis and with the complications of aortic regurgitation and stroke [27].

 

CT is indicated when evaluating other complications of transcatheter procedures. These include paravalvular leakage, (PVL) which is the leaking of blood through 'gaps' left between the prosthesis and cardiac tissue [34]. CT analysis generates ratings based on the density of calcium in and around the relevant tissues (also known as the Agatston score) [34]. This is regarded as the most accurate indicator of PVL [34].

 

 

Discussion

 

 

Damage or dysfunction of the aorta is a relatively rare phenomenon that appears to affect far fewer patients than other pathologies of the chest or abdomen. However, figures estimating the incidence of the pathologies as above may be related to a low success rate in their accurate diagnosis, and possibly also due to unacknowledged or misattributed symptoms. On the other hand, aortic pathology may be related to an extensive potential for morbidity and mortality when present. Interruptions to aortic pathology may affect the continued health and function of many organs, as their major arteries branch off from and are directly supplied by this vessel. Aortic pathology may have consequences such as kidney failure, tissue ischemia and generalised blood loss in the thorax and abdomen [25].

 

Aortic pathology may also be associated with other complications such as paraplegia, due to the deprivation of or damage to vertebral arteries [25]. The current low rate at which aortic pathology is detected may indicate an increased need for imaging studies in cases presenting the symptoms and complications as above. Imaging in the assessment of confirmed aortic disease is frequent and common, yet there is a chance that it is underused at the diagnostic stage. On the other hand, it must be pointed out that data on incidence and prevalence is based on screening programs, which are subject to available resources, and those patients with access to them [17]. Screening is also mainly directed at age groups currently perceived to be at high risk of aortic pathologies. There is a wide range of imaging options available, the choice of which depends on the type of aortic pathology that is suspected to be present, and must furthermore be optimized based on patient characteristics [6]. The R.T.’s responsibility is to take these into account.

 

CTA, MRA and US are demonstrably accepted as standard components of the assessment and follow-up involved in the management of aortic pathology. Similarly, it is clear that plain radiography, while commonly available and popular in many first-line and routine care settings, has been supplanted by these newer modalities. On the other hand, some researchers assert that it could replace CTA in some situations, e.g. the first post-operative imaging study following an aortic dissection, but only as part of a multimodal approach to this standard procedure [8]. CTA remains the widely-recognized standard in the assessment of aortic dissection, aneurysm and the complications of their treatment. Long-term evaluation and experimentation with other forms of CT and multimodal imaging may help to reduce risks such as cumulative radiation exposure. Emerging techniques such as aortic FDG-PET and SPECT may also offer viable alternatives to routine CTA. The role of CTA may even be re-assigned to diagnostic imaging and first-line imaging. As things stand now, the descriptive and quantitative power of this technique is likely to see CTA retain its status in the study and evaluation of aortic pathology for some time to come. This technique poses demonstrable risks to patients with severe pre-existing kidney damage due to the relatively large volume of contrast material required to image the whole aorta [25]. On the other hand, one researcher claims that 64-slice CT can be successfully delivered using as little as 40ml of contrast material [25]. This may indicate the validity of studies optimizing minimal contrast volumes in proportion to slice numbers.

 

 

Conclusion

 

Aortic pathology is a potentially serious form of disease in which the absence of swift and accurate diagnosis may lead to death or considerable reductions in life quality. The role of imaging in the assessment of aortic disease is relatively clear-cut in many healthcare settings. It is indicated in the diagnosis of aortic pathology, particularly in cases of trauma or in patients who fall into high-risk demographics. Furthermore, it is likely to be a regular feature in the lives of patients afterward, as these individuals often require long-term assessment for changes in their condition and for complications following various surgical treatments. If there is uncertainty concerning aortic imaging, it is in which technique should be employed, and at which stages of assessment. CTA may be the most powerful and effective imaging type when visualizing aortic damage and dysfunction. However, it is also often the most expensive, and is associated with higher risks for some patients. In these cases, the R.T. may need to consider alternatives when conducting repeat examinations. Replacements for CTA may include ultrasound, MRA, MRI, conventional CT and plain radiography. A practitioner may also consider multimodal imaging, which is a strategic combination of some of these techniques. Another possibility lies in reducing the volume of contrast material while increasing the number of slices. This may reduce scan times, but also sacrifice resolution in one axis. These options may also be limited by the hardware and other resources available.

 

This article is intended to outline and describe some forms of aortic pathology and their detection through imaging. This area is still largely dominated by 'traditional' techniques such as specific variations in CT (i.e. CTA) and ultrasound (i.e. echocardiography). An R.T. may make use of this to improve their understanding of aortic disease, its visualization and the decisions to be made in delivering imaging relevant to this.

 

 

References

 

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