Coronary artery aneurysms are defined as localized vessel dilatation exceeding 50% of the adjacent normal coronary artery diameter. A precise definition of the threshold between aneurysm and “giant” aneurysm is not well established, but some authors have suggested that aneurysms > 20 mm meet this criteria. Giant coronary artery aneurysms are identified by the presence of a round or ovoid structure on the epicardial surface of the heart in the typical location for coronary arteries. Often discovered incidentally on echocardiogram, they will appear as a paracardiac mass with varying degrees of flow on Doppler interrogation depending on presence of thrombus. On non-contrast CT, they are low- attenuation, rounded masses that may have peripheral calcifications related to atherosclerosis. After contrast administration, lesions will enhance similar to blood pool, although varying degrees of thrombosis may be present (Figure 38.1). Large aneurysms can erroneously appear thrombosed on cardiac CT due to incomplete filling at the time of arterial phase acquisition (Figure 38.2). Delayed venous images will demon- strate further fill-in of the aneurysm. Cardiovascular magnetic resonance (CMR) imaging will typically show low signal on dark blood images due to flow (Figure 38.1). Steady-state free precession (SSFP) and contrast injections with gadolinium will confirm high signal in the structure due to blood and may show evidence of thrombus (Figures 38.1 and 38.2).
Patients with giant coronary aneurysms may present with life-threatening tamponade due to rupture. Thrombosis, fistulization to cardiac chambers, and embolization have also been noted in the literature. Giant coronary artery aneurysms can be misinterpreted as cardiac tumors, particularly if only limited imaging is available. The distinction between tumor and aneurysm could have significant impact on treatment.
Typical clinical scenario
Coronary artery aneurysms more commonly affect males and have an incidence between 0.3% and 5%. Coronary aneurysms greater than 20 mm are extremely rare and in one series represented only 0.02% of patients undergoing cardiac surgery. They are more likely to involve the right coronary artery.
Unroofed coronary sinus is a communication between the coronary sinus and left atrium. The result is a left-to-right shunt that allows flow of oxygenated blood from the left atrium into the coronary sinus. In the normal situation, the coronary sinus courses inferior to the undersurface of the left atrium in the left atrioventricular groove, emptying into the right atrium. In unroofed coronary sinus there is a variably sized communication between the two structures (Figure 24.1). In partial unroofing, a single or several small orifices are seen. In complete unroofing, there is total absence of the tissue separating the left atrium and coronary sinus. At crosssectional imaging, defects are optimally visualized in a shortaxis plane parallel to the atrioventricular groove (Figure 24.2). Associated signs include enlargement of the right atrium and right ventricle due to shunting, which can be quantified using phase-contrast MRI. In the case of small restrictive defects, turbulent flow jets may be visualized in the left atrium on cardiac MRI.
Unroofed coronary sinus is a rare cause for left-to-right shunt. It may be challenging to make the diagnosis on transthoracic echocardiography due to limited imaging windows, resulting in referral of patients to cardiac CT or MRI to evaluate for occult shunt. Diagnosis is important due to potential for transient right-to-left shunting that can result in systemic emboli or brain abscess.
Typical clinical scenario
Unroofed coronary sinus is a rare disorder that is the least common type of atrial septal defect, representing less than 1% of these anomalies. There is a frequent association with left-sided superior vena cava, which is seen in approximately 63–75% of cases. Many patients will have additional congenital cardiac defects.
Unroofed coronary sinus should be distinguished from other types of potentially difficult to diagnose left-to-right shunts, such as sinus venosus atrial septal defects and partial anomalous pulmonary venous return.
The pulmonary endothelium, poised at the interface between air, blood, and tissue, provides both rapid and sustained responses to local and systemic perturbations. This complex vascular structure occupies a surface area of 120m2 and forms the intimal lining of the pulmonary arterial, venous, and capillary beds with a single continuous layer of endothelial cells (ECs) linked to each other by specialized junctions (1). The alveolar endothelium is intimately related to the alveolar epithelium both in terms of anatomic location and functions that include oxygen (O2), carbon dioxide, water and solute transport, and barrier regulation; disruption of barrier functions of the alveolar capillary membrane is an early and critical event in the pathogenesis of acute respiratory distress syndrome (ARDS) (see later and Box 128.1). Alveolar epithelial function, which is beyond the scope of this chapter, has recently been reviewed (2).
Once thought of as passive, semipermeable conduits for nutrient and O2 delivery – and in the lungs, contributing to separation of blood from air (1) (Box 128.1) – ECs were dismissed as structural bystanders with little or no capacity to respond to activating signals with changes in phenotype or function (3). During the 1950s, electron microscopic observations that ECs contain secretory granules, together with ongoing physiological studies of EC–leukocyte interactions, implicated the endothelium as an active participant in both physiological and pathophysiological responses to injury and inflammation (4–6). Subsequent studies clearly demonstrated that, even under normal physiological conditions, the “quiescent” endothelium is far from inactive and is involved in multiple homeostatic functions. These include, but are not limited to, cellular and nutrient trafficking, angiogenesis and vasculogenesis, regulation of vascular tone, and maintenance of blood fluidity and vascular barrier function (3–7).
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