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Cardiac Aneurysms and Diverticula: Magnetic Resonance and Computed Tomography Appearances
Cardiac Aneurysms and Diverticula: Magnetic Resonance and Computed Tomography Appearances Edward T.D. Hoey, MBBCh, BAO, MRCP, FRCR, Inderjeet Nagra, MBBS, FRCR, and Arul Ganeshan, BSc, MBBCh, MRCP, FRCR
Echocardiography is the first-line imaging modality for assessment of structural heart disease but magnetic resonance imaging and multi-detector computed tomography are being increasingly used for cardiac morphologic assessment. Aneurysms and diverticulae of the cardiac chambers and related structures represent a diverse group of conditions with varying etiologies and clinical manifestations. This article reviews the magnetic resonance imaging and multi-detector computed tomography features of these lesions with consideration of the emerging role that crosssectional imaging has to play in their evaluation. Radiologists should be familiar with the salient imaging appearances of these conditions to facilitate optimal patient management.
Aneurysms and diverticula that involve cardiac and paracardiac structures comprise a diverse group of conditions with varying etiologies and clinical manifestations. Some are incidental findings of little clinical importance, while others can be acutely lifethreatening and present dramatically with sudden hemodynamic collapse. Echocardiography and catheter angiography have for many years formed the cornerstone of cardiac imaging but cardiovascular magnetic resonance (CMR) and multi-detector computed tomography (MDCT) are becoming increasingly important modalities in the assessment of cardiac pathology. In this review we present the spectrum of cardiac aneurysms and diverticula as demonstrated by
CMR and MDCT. For the purpose of this article, these lesions have been classified according to anatomical location, ie, cardiac chambers, septum, great vessels, and coronary vasculature.
Noninvasive Imaging Techniques An abnormal chest x-ray may raise suspicion of an underlying aneurysm or large diverticulum and there may be secondary signs on the film that point to a specific cause, eg, calcification following the outline of the left ventricle in ischemic cardiomyopathy, but its main role is to provide a baseline assessment of heart size and to assess for pulmonary edema. Transthoracic echocardiography (TTE) has traditionally been the most useful means of assessing cardiac morphology and function but suffers from several well-described limitations including heavy operator dependency and a somewhat restricted field of view (especially in patients with chronic obstructive pulmonary disease), which may preclude complete structural assessment. In particular, TTE struggles to image the left ventricular apex and right ventricle, which are “near field” structures.1 Transesophageal echocardiography can overcome some of the limitations of TTE but is semi-invasive, requires a highly skilled operator, and may not be suitable in high-risk patients.
Cardiovascular Magnetic Resonance From the Heart of England NHS Foundation Trust, Birmingham, West Midlands, UK. Reprint requests: Arul Ganeshan, BSc, MBBCh, MRCP, FRCR, Heart of England NHS Foundation Trust, Birmingham, West Midlands, B5 4SS, UK. E-mail: [email protected]. Curr Probl Diagn Radiol 2011;40:72-84. © 2011 Mosby, Inc. All rights reserved. 0363-0188/$36.00 ⫹ 0 doi:10.1067/j.cpradiol.2010.02.001
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CMR is the reference technique for cardiac morphologic assessment and quantification of biventricular function with several advantages over TTE including an unrestricted field of view and ability to image in any desired plane.1,2 Static “black blood” prepared T1and T2-weighted sequences are used for tissue characterization, while dynamic “bright blood” prepared
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steady-state free precession (SSFP) sequences provide high temporal resolution for cine visualization of contractile function. Several additional sequences can be employed such as a T1-weighted inversion recovery, typically acquired 10-15 minutes following administration of 0.1 mmol/kg gadolinium, for assessment of myocardial scar and infiltrative processes.3 Velocity-encoded phase-contrast sequences are used to assess flow and permit quantification of any associated intracardiac shunting.2 Limitations of CMR include its contraindications (eg, implanted ferromagnetic device) and relatively long acquisition times (30-60 minutes for a typical structural assessment protocol). CMR has inferior spatial resolution (1.0-2.0 mm) compared with MDCT (0.4-0.6 mm) and cannot reliably assess calcification; as such it is inferior for the assessment of coronary artery atherosclerosis.
Multi-Detector Computed Tomography Technological advances in recent years, including improvements in spatial and temporal resolution and the introduction of electrocardiographic (ECG) gating, have made MDCT a powerful tool in its own right for cardiac morphologic assessment.4 Although it is unable to provide flow information, most other aspects of a CMR study can be assessed. A complete MDCT dataset can usually be acquired in a single breathhold, which is particularly advantageous in patients with orthopnea or claustrophobia. Examinations at our institution are performed on a state-of-the-art 320-row computed tomographic (CT) scanner with 0.5-mm detector elements and 350-ms gantry rotation time (Aquilion ONE, Toshiba Medical Systems, Otawara, Japan). This system permits up to 16 cm of coverage in the z-axis direction per rotation and therefore “whole heart coverage” in a single snapshot.5 It can also be operated in spiral mode using 64-detector elements for extended volume coverage. For dedicated cardiac CT angiography, we routinely perform a volume acquisition with coverage from carina to cardiac apex. Prospective ECG-triggering with an acquisition window from 70% to 100% of the RR interval is used in patients with heart rates ⬍65 bpm and 35%-100% for heart rates ⬎65 bpm.5 Retrospective ECG-gating is used for functional analysis whereby cine loops can be reconstructed for dynamic visualization of valvular function and calculation of left ventricular functional parameters. Coronary CT angiography is emerging as a valid alternative to cardiac catheterization in selected patient groups and as it also provides extraluminal
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information is especially useful for visualizing tortuous or anomalous vascular anatomy. The main drawback of MDCT is its attendant radiation burden, especially for coverage of the entire thorax, although dose reduction strategies such as ECG-gated current modulation continue to evolve.6 Although ECG-gating improves confidence in assessment, many of the lesions presented in this article may be readily appreciated on nongated acquisitions.
Left Ventricle Aneurysm Left ventricular aneurysm is defined as a distinct area of abnormal left ventricular diastolic contour with systolic dyskinesia or paradoxical bulging.7 True left ventricular aneurysms involve the full thickness of the left ventricular wall, while a false aneurysm represents a localized rupture contained by pericardial adhesions. The vast majority of aneurysms relate to coronary artery disease with a small proportion caused by trauma, sarcoidosis, or other form of cardiomyopathy.7 The incidence of true left ventricular aneurysms in patients with prior myocardial infarction may be as high as 10%-25%, although this is probably in decline with the increased use of thrombolytics and primary revascularization.8 False aneurysms result from ventricular rupture, which typically occurs 5-10 days following myocardial infarction. Ventricular aneurysms diminish systolic and diastolic function, increase myocardial oxygen demand, and decrease cardiac output because of volume loading.8 Untreated, the natural history of true and false aneurysms is progressive enlargement with its attendant complications. False aneurysms are associated with a much higher risk of free rupture and sudden death and operative repair is generally advocated; true aneurysms are more often managed medically with or without concomitant revascularization.8 Other recognized complications include in situ thrombosis with systemic embolization, ventricular arrhythmias, and stretching of the mitral valve leading to regurgitation. Several imaging features help differentiate a true from false aneurysm. False aneurysms usually have a mouth that is considerably smaller than the maximal aneurysmal diameter and most often occur in the circumflex coronary artery territory, ie, along the inferolateral wall (Fig 1). Also, a recent article has suggested that diffuse pericardial enhancement as
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FIG 1. False aneurysm of the left ventricle in a 76-year-old man with a prior history of circumflex coronary artery territory infarction. (A) Axial CT image. The aneurysm has a narrow neck from the left ventricle (LV) and is contained by pericardium (arrows). It contains partially calcified mural thrombus (*). (B) Volume-rendered 3-dimensional reconstruction showing the same with margins of the aneurysm marked by arrows. LV ⫽ left ventricle; LA ⫽ left atrium. (Color version of figure is available online.)
assessed by CMR may be a characteristic feature of false aneurysms.9 Up to 90% of true aneurysms result from full-thickness infarction in the left anterior descending coronary artery territory and they therefore predominate along the anterior wall and apex (Fig 2).8
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FIG 2. True aneurysm of the left ventricle in a 65-year-old man with a prior history of left anterior descending coronary artery territory infarction. (A) Four-chamber SSFP CMR image in systole showing paradoxical “bulging” of the left ventricular apex (arrows). (B) Fourchamber T1-weighted delayed enhancement CMR image acquired 10 minutes following administration of gadolinium-based contrast agent and with an inversion recovery pulse sequence to null signal from normal myocardium. There is full-thickness enhancement at the apex in keeping with transmural infarction (arrows); in addition, there is low-signal mural thrombus (arrowhead). LV ⫽ left ventricle.
Some nonischemic left ventricular aneurysms have fairly characteristic CMR/MDCT features, particularly those in association with hypertrophic cardiomyopathy (HCM). HCM can predominantly involve the middle
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third of the left ventricle and is associated with formation of an apical aneurysm that is thought to result from generation of increased midventricular systolic pressures, so-called “burnt out apex.”10 A similar appearance is also recognized in apical variant HCM and has been attributed to longstanding smallvessel ischemia.10 Supportive imaging features for HCM include cavity obliteration in systole and patchy midwall delayed gadolinium enhancement. Takotsubo cardiomyopathy, also known as transient apical ballooning syndrome, is another form of nonischemic cardiomyopathy associated with aneurysmal left ventricular dilatation. It is postulated to be caused by high circulating catecholamine levels as may occur at times of severe emotional stress and typically presents with chest pain and ECG changes suggestive of anterior wall myocardial infarction.11 Its imaging hallmark is apical dyskinesia with preserved or hypercontractile basal function and the coronary arteries are nonobstructed.12 CMR shows no signs of infarction or infiltration and left ventricular function usually fully recovers with normalization by 2-3 months.12 Left ventricular mural thrombus occurs in up to 40% of patients with a dyskinetic ventricular segment. On CMR signal intensity of thrombus varies with age on T1- and T2-weighted images and delayed gadolinium enhancement images are most helpful for making a confident diagnosis whereby thrombus appears of low signal compared with adjacent tissues4 (Fig 2B). On MDCT thrombus appears as a laminated lowattenuation lesion abutting the often thinned myocardium (Fig 1A).
Diverticulum Left ventricular diverticulum is an outpouching that has walls composed of predominantly myocardial tissue and involves at least half of the compacted myocardial wall thickness.13 The reported prevalence is 0.3%-2% with diverticula described in the literature ranging in size from 0.5 to 8 cm.8 The majority are thought to be congenital in nature and they are usually asymptomatic, being discovered incidentally during diagnostic imaging procedures performed for other reasons.13 There is a postulated association with ventricular arrhythmias and cardioembolic embolism but no direct link has been established. MDCT affords the highest spatial resolution of the noninvasive imaging modalities and ventricular diverticula are increasingly reported as ancillary findings in
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FIG 3. Left ventricular diverticulum as an incidental finding in a 55-year-old man undergoing CMR for assessment of myocardial ischemia. (A) Four-chamber SSFP CMR image showing a diverticulum involving the distal portion of the interventricular septum (arrow). (B) Short-axis SSFP CMR image showing the same (arrows). LV ⫽ left ventricle.
patients undergoing ECG-gated coronary CT angiography.13 They are most commonly found at the apex and perivalvular areas, although they have been reported in nearly all regions. Ventricular diverticula are occasional findings on CMR studies (Fig 3).
Right Ventricle Right ventricular aneurysm is unusual as it is the left coronary circulation that more often undergoes infarction; a 0.08% incidence has been reported following myocardial infarction.14 Other causes include trauma and arrthymogenic right ventricular cardiomyopathy (ARVC). ARVC is a disease complex characterized by
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FIG 4. Focal dyskinetic segment of the right ventricular free wall in a 36-year-old woman with a diagnosis of ARVC. Axial SSFP CMR image in systole showing a focal dyskinetic segment of the right ventricular free wall (arrow).
gradual loss of right ventricular myocytes and replacement by adipose and fibrous tissue with subsequent dilatation, dysfunction, and potential for electrical instability.15 The latter predisposes to ventricular arrhythmias and sudden death, most often in young adults. ARVC has an estimated incidence of 1 in 5000 of whom around 50% will have a positive family history.16 Diagnosis relies on a combined assessment of clinical, genetic, histologic, and imaging-based abnormalities. CMR is the imaging modality of choice with the most sensitive markers of ARVC being right ventricular systolic dysfunction (right ventricular ejection fraction ⬍50%) and regional wall motion abnormality, which may constitute a focal dyskinetic (aneurysmal) segment (Fig 4).15 The inflow, outflow, and apical portions of the right ventricle are most often affected, the so-called “triangle of dysplasia.” The identification of macroscopic intramyocardial fat adds confidence to making the diagnosis but will only be visible in around 60% of cases.17 ECG-gated MDCT is an alternative to CMR in patients who are precluded from undergoing MRI examination (Fig 5).15
Left Atrium Aneurysm The left atrium normally measures less than 4.5 cm in anteroposterior dimension and is considered aneurysmal when its diameter exceeds 6 cm.18 There are many causes of left atrial enlargement but it most
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FIG 5. Fatty infiltration of the right ventricular free wall in a 25-year-old woman with a presumptive clinical diagnosis of ARVC. Axial MDCT image showing macroscopic fat deposition (arrows). RV ⫽ right ventricle. (Color version of figure is available online.)
frequently occurs secondary to ischemic cardiomyopathy whereby the left ventricle dilates, causing distortion of the mitral subvalvular apparatus with resultant mitral regurgitation.19 Mitral stenosis is another frequent cause of left atrial enlargement, most commonly occurring as a late sequelae of rheumatic heart disease. CMR is the modality of choice for assessing left ventricular function, while dynamic perfusion and delayed gadolinium enhancement sequences permit assessment of ischemia and infarction, respectively.19 Ischemic left ventricular dysfunction results in cavity dilatation (diastolic dimension ⬎5.5 cm) and wall thinning, which are readily appreciated. Hallmark imaging features of mitral stenosis are thickening and retraction of the valve leaflets and chordae tendinae in association with left atrial enlargement (Fig 6).20 MDCT and CMR can also be used to assess mitral stenosis severity by planimetry of the orifice opening area, whereby a diastolic area less than 2 cm2 is considered clinically significant.20
Diverticulum Left atrial diverticula are highly prevalent, being reported in 15%-25% of all ECG-gated cardiac CT examinations.21 They are thought to represent anatomical variants rather than pathologic findings and in the
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FIG 6. Rheumatic mitral stenosis with gross biatrial enlargement in a 31-year-old woman with rheumatic mitral stenosis. Axial MDCT image showing pronounced thickening of the posterior mitral valve leaflet (arrow). LA ⫽ left atrium; RA ⫽ right atrium.
FIG 7. Left atrial diverticulum as an incidental finding in a 55-year-old woman undergoing cardiac CT angiography for investigation of chest pain. Axial MDCT image showing characteristic location and appearances (arrow). LA ⫽ left atrium; Ao ⫽ aortic root.
majority of instances are not associated with other congenital cardiac anomalies.21 What role they may have in the development of atrial fibrillation or an increased prevalence of thromboembolic disease remains the subject of ongoing debate. An atrial diverticulum is recognized by its “saclike” shape, broad-based ostium, and smooth wall contour. The majority measure between 3 and 10 mm in maximal dimension and are most often located in a superior anterior location (Fig 7).21 An accessory left atrial appendage can have a similar appearance but its wall contour is typically irregular, owing to the presence of fine pectinate muscles, and they are more frequently found in an inferior left lateral location.21
pid valve leaflet with resultant “atrialization” of the right ventricle (Fig 8).23 Other causes of right atrial enlargement include pulmonary valve stenosis or regurgitation and any cause of pulmonary arterial hypertension including left to right shunts. Right atrial enlargement can cause palpitations and atrial arrhythmias.23 CMR is the modality of choice for assessment of the tricuspid valve, right heart chambers, and any associated congenital cardiac anomalies; however, ECG-gated cardiac MDCT has an emerging role in those patients in whom CMR is contraindicated.
Right Atrium Aneurysm The right atrium normally measures less than 3.5 cm in transverse dimension and is considered aneurysmal when its diameter exceeds 5.5 cm.22 There are a wide range of conditions that may be associated with right atrial enlargement, including primary disorders of the tricuspid valve such as Ebstein’s anomaly in which there is apical displacement of the septal tricus-
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Diverticulum Right atrial diverticulum is a thin-walled outpouching from the right atrial free wall that histologically consists of fibrous tissue and intima and lacks a muscular component that distinguishes it from right atrial aneurysm.24 The etiology remains incompletely understood and many cases probably remain subclinical. Large diverticula have the potential to rupture, develop in situ thrombosis, and cause symptomatic compression of the right ventricle. A recent review of reported cases indicated a 6% risk of sudden cardiac death and concluded that surgical resection should be performed in those who become symptomatic.23 Both CMR and MDCT can be used to confirm the diagnosis
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FIG 8. Ebstein’s anomaly in a 28-year-old man in whom CMR evaluation was precluded by claustrophobia. Axial MDCT imaging showing displacement of the tricuspid valve leaflets (arrows) deep into the “atrialized” right ventricle. RA ⫽ right atrium; RV ⫽ right ventricle.
whereby the diverticulum communicates via a narrow opening that can be solitary or fenestrated (Fig 9).
Interatrial Septum Excessive mobility of the interatrial septum or membranous portion of the interventricular septum is termed cardiac septal aneurysm when the protrusion extends ⬎10 mm beyond the septal plane.25 The prevalence is reported as 0.2%-3% in the general population and there is an association with patent foramen ovale with consequent right to left shunting and increased risk of stroke, which may be as high as 3.8% per annum.26 Septal aneurysm is best appreciated on review of cine sequences from ECG-gated MDCT or CMR examinations, which can clearly depict dynamic septal bowing (Fig 10). Dynamic contrast-enhanced CMR and more recently ECG-gated MDCT, using a saline flush, have been shown as accurate means of patent foramen ovale detection.27
Aortic Root The sinuses of Valsalva (SOV) are 3 focal expansions that form the walls of the aortic root. They give rise to
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FIG 9. Right atrial diverticulum in a 52-year-old man who presented with chest pain. (A) Chest x-ray showing “bulging” right heart border (arrows). (B) Axial SSFP CMR image showing large blood-filled cavity compressing the right ventricle (*) and a small pericardial effusion. (C) Axial SSFP CMR image showing multiple fenestrated openings (arrows) between the right atrial free wall and the diverticulum (*). Also, note the small pericardial effusion. RA ⫽ right atrium.
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FIG 10. Atrial septal aneurysm in a 66-year-old man with a prior history of myocardial infarction. Four-chamber SSFP CMR image showing pronounced “bowing” of the interatrial septum into the right atrium (arrows). LA ⫽ left atrium.
the right and left coronary artery ostia (with the exception of the noncoronary sinus) and function as a support structure for the aortic valve.28 The aortic root can be focally or globally dilated. Focal dilation or 1 or 2 sinuses is classified as SOV aneurysm, whereas dilation of all 3 sinuses is classified as aortic root aneurysm.29 SOV aneurysms are rare anomalies with an estimated prevalence of 0.17%.29 The majority are congenital, resulting from a deficiency of elastic lamellae in the sinus wall, which gradually gives way under high-pressure flow, leading to progressive aneurysmal dilatation and eventually rupture.30 Unruptured aneurysms are usually clinically silent and most are discovered serendipitously on echocardiography performed for another indication.31 Rupture often presents dramatically with sudden hemodynamic collapse but can have a more insidious onset depending on its site and size.30 Aneurysms most commonly originate from the right coronary sinus (80%); less commonly from the noncoronary sinus (15%), and rarely from the left sinus (5%).29 TTE is the modality of choice in the setting of suspected acute SOV rupture; however, MDCT and CMR are being increasingly used in the nonemergent setting to delineate anatomy and relationship to surrounding structures. Owing to its high spatial resolution, ECG-gated MDCT is an excellent means of assessment with SOV aneurysm appearing as a thinwalled crescent-shaped outpouching (Fig 11).32 The
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FIG 11. Sinus of Valsalva aneurysm in a 36-year-old man who presented acutely with chest pain and dyspnea. Axial MDCT image showing a large crescent-shaped structure that extends deep into the left atrium (arrows). Also, note bilateral pleural effusions secondary to decompensation from aorto-left atrial fistula, which was confirmed at surgery. LA ⫽ left atrium; LV ⫽ left ventricle.
principle advantages of CMR are its ability to quantify any associated aortic regurgitation and, in the setting of chronic rupture, into the right heart chambers when shunt fraction can be estimated using phase-contrast imaging performed through the proximal aorta and pulmonary artery. Aortic root aneurysm is commonly caused by conditions associated with annulo-aortic ectasia such as Marfan syndrome and other connective tissue disorders.33 Annulo-aortic ectasia is characterized by progressive enlargement of all 3 sinuses in conjunction with effacement of the sinotubular junction to give a “tulip bulb” appearance (Fig 12).29 Stretching of the aortic valve apparatus invariably leads to aortic regurgitation and left ventricular volume overload. Aortic root dimensions are best measured in a coronal oblique plane to achieve reproducible results; maximal SOV dimension should not exceed 4 cm in a male and 3.6 cm in a female.34
Main Pulmonary Artery The main pulmonary artery (MPA) is dilated when its maximal diameter exceeds 3 cm and its left and
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FIG 12. Aneurysm of the aortic root and ascending thoracic aorta in a 38-year-old man with Marfan syndrome. (A) Axial black blood prepared CMR image showing pronounced dilatation of the aortic root. (B) Volume-rendered 3-dimensional magnetic resonance angiogram image showing fusiform dilatation of the aortic root and ascending aorta with loss of the normal “waisting” at the sinotubular junction. Ao ⫽ aorta.
right main branches normally measure ⬍2 cm in an adult.35 The MPA can become aneurysmal secondary to longstanding pulmonary arterial hypertension of which the causes are diverse and include chronic thromboembolic disease, left to right shunts, and smallvessel vasculopathies.36 Several congenital defects associated with pulmonary valve stenosis may cause the pulmonary artery to become aneurismal, including tetralogy of Fallot. MPA dimension is conventionally measured at its bifurcation in the axial plane.36 MDCT pulmonary angiography is fast becoming the reference technique for assessment of pulmonary arterial hypertension in which partially calcified laminated “in situ” thrombus
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FIG 13. Aneurysmal dilatation of the main pulmonary artery in a 52-year-old woman with untreated ostium secundum type atrial septal defect. (A) Axial black blood prepared CMR image showing pronounced dilatation of the main pulmonary artery (5 cm maximal transverse diameter). (B) Volume-rendered 3-dimensional magnetic resonance angiogram image showing gross dilatation of the main pulmonary artery and proximal branches. PA ⫽ pulmonary artery.
is often seen lining the proximal pulmonary artery branches. CMR is the reference technique for assessment of congenital heart disease and pulmonary valve stenosis severity can be quantified using phase-contrast sequences. In addition, magnetic resonance angiography can be used to make assessment of the proximal pulmonary vasculature (Fig 13).
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ital in origin and most often originate from the right coronary artery with drainage to the right-sided cardiac chambers or pulmonary artery (Fig 15). With catheter coronary angiography, only intraluminal flow can be evaluated, and no information is provided about the vessel wall; thus, the true size of an aneurysm may be underestimated and in some cases an aneurysm may not even be seen when it is occluded or contains a substantial amount of thrombus.42 MDCT coronary angiography is an excellent means of assessing anomalous course and termination of coronary vessels and the extraluminal information that it provides is particularly useful for evaluating aneurysms. Coronary aneuryms are occasional findings on CMR studies and should not be confused with an extracardiac mass (Fig 16).4
FIG 14. Coronary artery aneurysm in a 24-year-old man with a history of Kawasaki disease in childhood for which he required coronary artery bypass grafting. Axial MDCT image showing an aneurysm of the left anterior descending coronary artery, which contains extensive partially calcified mural thrombus (arrows). Ao ⫽ aorta.
Coronary Arteries A coronary artery aneurysm is when the maximal diameter of a coronary vessel is increased by 1.5 times the normal diameter with involvement of less than 50% of the vessel length.37 The reported frequency is 0.3%-5% from post mortem studies.38 Atherosclerosis is by far the commonest cause and is thought to predispose to aneurysmal dilatation via turbulent flow and increased wall stress.39 Less common causes include coronary artery fistulas and vasculitides such as Takayasu arteritis and Kawasaki disease. Kawasaki disease is an acute self-limited multisystemic panarteritis that is most prevalent in Japan.40 Coronary artery aneurysms have been reported in 15%-25% of untreated cases and may be complicated by in situ thrombosis with arterial stenosis or occlusion (Fig 14).40 Takayasu arteritis is a large-vessel vasculitis more frequently seen in young women that is characterized by disruption of elastic fibers with marked thinning of the tunica media.41 It has a predilection for the great vessels but coronary involvement is reported in 10%15% of cases.41 A coronary artery fistula is defined as a connection between a coronary artery and a cardiac chamber or great vessel, with the connection bypassing the myocardial capillary bed.42 Most fistulas are congen-
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Coronary Veins and Bypass Grafts The coronary sinus is a channel through which the epicardial veins drain to the right atrium. Coronary sinus aneurysms or diverticulae are venous outpouchings located within the epicardial layers of the posterior ventricular septum. They are associated with accessory conduction pathways and supraventricular reentrant tachycardia.43 The coronary sinus may also be enlarged in association with congenital anomalies such as persistent left-sided superior vena cava and coronary sinus atrial septal defect (a defect in the sinus roof that permits interatrial shunting). Both MDCT and CMR can depict enlargement of the sinus and any associated structural abnormalities. Saphenous vein graft pseudoaneurysm is a wellrecognized late complication of coronary artery bypass grafting and has been attributed to vascular trauma at time of harvesting or implantation.44 The proximal graft anastomotic site is most commonly affected (Fig 17). Large aneurysms may be first detected on routine chest x-ray as patients not infrequently remain symptom free.45 MDCT is the modality of choice for further assessment and typically reveals a well-circumscribed mass with partial or complete contrast medium enhancement depending on the degree of intimal thrombosis.45 Treatment options include surgical resection, coil embolization, or a conservative approach, especially in patients who are asymptomatic.
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FIG 16. Right coronary artery aneurysm in a 50-year-old man in whom a right ventricular mass was identified on echocardiography. Axial SSFP CMR image showing a smoothly marginated mass indenting the right ventricular free wall (arrows).
FIG 17. Saphenous vein graft aneurysm in a 68-year-old man. Axial MDCT image showing dilatation of the graft at its origin from the ascending thoracic aorta (arrows). Ao ⫽ aorta.
4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™ FIG 15. Left coronary artery to pulmonary artery fistula in a 44-year-old man undergoing cardiac MDCT for investigation of chest pain. (A) Axial MDCT image at the level of the aortic root showing several tortuous dilated vessels (arrows) that were arising from the left anterior descending coronary artery. (B) Axial MDCT image at the level of the pulmonary artery showing fistulous communication and a focal aneurysm (arrows). (C) Volume-rendered 3-dimensional reconstruction showing the fistulous vessels coursing anterior to the pulmonary artery. Ao ⫽ aorta; PA ⫽ pulmonary artery. (Color version of figure is available online.)
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Conclusions Advances in MRI and MDCT have made them attractive tools for cardiac morphologic assessment. Highresolution images can be routinely acquired, enabling accurate characterization of any anatomical derangement and its sequelae. Familiarity with the characteristic imaging features of cardiac aneurysms and diverticulae will help expediate their diagnosis.
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14. Incalzi RA, Capparella O, Gemma A, et al. Right ventricular aneurysm: A new prognostic indicator after a first acute myocardial infarction. Cardiology 1991;79:120-6. 15. Sparrow P, Merchant N, Provost Y, et al. Cardiac MRI ad CT features of inheritable and congenital conditions associated with sudden cardiac death. Eur Radiol 2009;19:259-70. 16. Maron BJ, Towbin JA, Thiene G, et al. Contemporary definitions and classification of the cardiomyopathies: An American Heart Association scientific statement from the Council on Clinical Cardiology, Heart Failure and Transplantation Committee; quality of Care and outcomes research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; and Council on Epidemiology and Prevention. Circulation 2006;113:1807-16. 17. Tandri H, Macedo R, Calkins H, et al. Role of magnetic resonance imaging in arrhythmogenic right ventricular dysplasia: Insights from the North American arrhythmogenic right ventricular dysplasia (ARVD/C) study. Am Heart J 2008;155:147-53. 18. Gradin-Frimmer G, Lassvik C, Nylander E, et al. Echocardiographic estimation of left atrial size from the apical view. Eur Heart J 1982;3:159-63. 19. Hoey ET, Gopalan D, Agrawal SK, et al. Chronic left ventricular failure: The role of imaging in diagnosis and planning of conventional and novel therapies. Clin Radiol 2009;3:238-49. 20. Ryan R, Abbara S, Colen RR, et al. Cardiac valve disease: Spectrum of findings on cardiac 64-MDCT. AJR Am J Roentgenol 2008;190:W294-303. 21. Abbara S, Mundo-Sagardia JA, Hoffmann U, et al. Cardiac CT assessment of left atrial accessory appendages and diverticula. AJR Am J Roentgenol 2009;193:807-12. 22. O’Callaghan JP, Heitzman RE, Somogy JW, et al. CT evaluation of pulmonary artery size. J Comput Assist Tomogr 1982;6:101-4. 23. Binder TM, Rosenhek R, Frank H, et al. Congenital malformations of the right atrium and the coronary sinus: an analysis based on 103 cases reported in the literature and two additional cases. Chest 2000;117:1740-8. 24. Kobza R, Oechslin E, Pretre R, et al. Enlargement of the right atrium-diverticulum or aneurysm? Eur J Echocardiogr 2003; 4:223-5. 25. Dodd JD, Aquino SL, Holmvang G, et al. Cardiac septal sneurysm mimicking pseudomass: Appearance on ECG gated cardiac MRI and MDCT. AJR Am J Roentgenol 2007;188: W550-553. 26. Mugge A, Daniel WG, Angermann C, et al. Atrial septal aneurysm in adult patients: A multicentre study using transthoracic and transoesophageal echocardiography. Circulation 1999;91:2785-92. 27. Williamson EE, Kirsch J, Araoz PA, et al. ECG-gated cardiac CT angiography using 64-MDCT for detection of patent foramen ovale. AJR Am J Roentgenol 2008;190:929-33. 28. Underwood MJ, El Khoury G, Deronck D, et al. The aortic root: Structure, function, and surgical reconstruction. Heart 2000;83:376-80. 29. Ring S. Congenital heart surgery nomenclature and database project: Aortic aneurysm, sinus of Valsalva aneurysm, and aortic dissection. Ann Thorac Surg 2000;69:S147-63.
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30. Swan L. Sinus of Valsalva aneurysms. In: Gatzoulis MA, Webb GD, Daubeney PEF, editors. Diagnosis and Management of Adult Congenital Heart Disease. London, UK: Churchill Livingstone, 2003. p. 239-44. 31. Wang ZJ, Zou CW, Li DC, et al. Surgical repair of sinus of Valsalva aneurysm in Asian patients. Ann Thorac Surg 2007; 84:156-60. 32. Bricker AO, Avutu B, Mohammed TL, et al. Valsalva sinus aneurysms: Findings at CT and MR imaging. Radiographics 2010;30:99-110. 33. Vargas HA, Hoey ETD, Gopalan D, et al. Congenital and acquired conditions of the aortic root: Multidetector computed tomography features. Postgrad Med J 2009;85:383-91. 34. Roman MJ, Devereux RB, Kramer-Fox R, et al. Two-dimensional echocardiographic aortic root dimensions in normal children and adults. Am J Cardiol 1989;8:507-12. 35. Tan RT, Kuzo R, Goodman LR, et al. Utility of CT scan for predicting pulmonary hypertension in patients with parenchymal lung disease. Chest 1998;113:1250-6. 36. Hoey ETD, Gopalan D, Agrawal SKB, et al. Cardiac causes of pulmonary arterial hypertension: Assessment with multidetector CT. Eur Radiol 2009;19:2557-68.
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37. Swayne P, Fisher L, Litwin P et al. Aneurysmal coronary disease. Circulation 1983;67:134-8. 38. Robertson T, Fisher L. Prognostic significance of coronary artery aneurysm and ectasia in the coronary artery surgery study (CASS) registry. Prog Clin Biol Res 1987;250:325-39. 39. Pahlavan PS, Niroomand F. Coronary artery aneurysm: A review. Clin Cardiol 2006;29:439-43. 40. Kato H, Sugimura T, Akagi T, et al. Long-term consequences of Kawasaki disease: A 10 to 21-year follow-up study of 594 patients. Circulation 1996;94:1379-85. 41. Panja M, Sarkar C, Kar AK, et al. Coronary artery lesions in Takayasu’s arteritis: Clinical and angiographic study. J Assoc Physicians India 1998;46:678-81. 42. Diaz-Zamudio M, Bacilio-Perez U, Herrera-Zarza MC, et al. Coronary artery aneurysms and ectasia: Role of CT angiography. Radiographics 2009;29:1939-54. 43. Bennett D, Hall M. Coronary sinus diverticulum containing posteroseptal accessory pathway. Heart 2001;86:539. 44. Gilkeson RC, Markowitz AH, Ciancibello L. Multisection CT evaluation of the reoperative cardiac surgery patient. Radiographics 2003;23:S3-17. 45. Hoey ET, Ganesh V, Gopalan D, et al. Vein graft pseudoaneurysm. Postgrad Med J 2009;85:166.
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Echocardiography is the first-line imaging modality for assessment of structural heart disease but magnetic resonance imaging and multi-detector computed tomography are being increasingly used for cardiac morphologic assessment. Aneurysms and diverticulae of the cardiac chambers and related structures represent a diverse group of conditions with varying etiologies and clinical manifestations. This article reviews the magnetic resonance imaging and multi-detector computed tomography features of these lesions with consideration of the emerging role that crosssectional imaging has to play in their evaluation. Radiologists should be familiar with the salient imaging appearances of these conditions to facilitate optimal patient management.
Aneurysms and diverticula that involve cardiac and paracardiac structures comprise a diverse group of conditions with varying etiologies and clinical manifestations. Some are incidental findings of little clinical importance, while others can be acutely lifethreatening and present dramatically with sudden hemodynamic collapse. Echocardiography and catheter angiography have for many years formed the cornerstone of cardiac imaging but cardiovascular magnetic resonance (CMR) and multi-detector computed tomography (MDCT) are becoming increasingly important modalities in the assessment of cardiac pathology. In this review we present the spectrum of cardiac aneurysms and diverticula as demonstrated by
CMR and MDCT. For the purpose of this article, these lesions have been classified according to anatomical location, ie, cardiac chambers, septum, great vessels, and coronary vasculature.
Noninvasive Imaging Techniques An abnormal chest x-ray may raise suspicion of an underlying aneurysm or large diverticulum and there may be secondary signs on the film that point to a specific cause, eg, calcification following the outline of the left ventricle in ischemic cardiomyopathy, but its main role is to provide a baseline assessment of heart size and to assess for pulmonary edema. Transthoracic echocardiography (TTE) has traditionally been the most useful means of assessing cardiac morphology and function but suffers from several well-described limitations including heavy operator dependency and a somewhat restricted field of view (especially in patients with chronic obstructive pulmonary disease), which may preclude complete structural assessment. In particular, TTE struggles to image the left ventricular apex and right ventricle, which are “near field” structures.1 Transesophageal echocardiography can overcome some of the limitations of TTE but is semi-invasive, requires a highly skilled operator, and may not be suitable in high-risk patients.
Cardiovascular Magnetic Resonance From the Heart of England NHS Foundation Trust, Birmingham, West Midlands, UK. Reprint requests: Arul Ganeshan, BSc, MBBCh, MRCP, FRCR, Heart of England NHS Foundation Trust, Birmingham, West Midlands, B5 4SS, UK. E-mail: [email protected]. Curr Probl Diagn Radiol 2011;40:72-84. © 2011 Mosby, Inc. All rights reserved. 0363-0188/$36.00 ⫹ 0 doi:10.1067/j.cpradiol.2010.02.001
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CMR is the reference technique for cardiac morphologic assessment and quantification of biventricular function with several advantages over TTE including an unrestricted field of view and ability to image in any desired plane.1,2 Static “black blood” prepared T1and T2-weighted sequences are used for tissue characterization, while dynamic “bright blood” prepared
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steady-state free precession (SSFP) sequences provide high temporal resolution for cine visualization of contractile function. Several additional sequences can be employed such as a T1-weighted inversion recovery, typically acquired 10-15 minutes following administration of 0.1 mmol/kg gadolinium, for assessment of myocardial scar and infiltrative processes.3 Velocity-encoded phase-contrast sequences are used to assess flow and permit quantification of any associated intracardiac shunting.2 Limitations of CMR include its contraindications (eg, implanted ferromagnetic device) and relatively long acquisition times (30-60 minutes for a typical structural assessment protocol). CMR has inferior spatial resolution (1.0-2.0 mm) compared with MDCT (0.4-0.6 mm) and cannot reliably assess calcification; as such it is inferior for the assessment of coronary artery atherosclerosis.
Multi-Detector Computed Tomography Technological advances in recent years, including improvements in spatial and temporal resolution and the introduction of electrocardiographic (ECG) gating, have made MDCT a powerful tool in its own right for cardiac morphologic assessment.4 Although it is unable to provide flow information, most other aspects of a CMR study can be assessed. A complete MDCT dataset can usually be acquired in a single breathhold, which is particularly advantageous in patients with orthopnea or claustrophobia. Examinations at our institution are performed on a state-of-the-art 320-row computed tomographic (CT) scanner with 0.5-mm detector elements and 350-ms gantry rotation time (Aquilion ONE, Toshiba Medical Systems, Otawara, Japan). This system permits up to 16 cm of coverage in the z-axis direction per rotation and therefore “whole heart coverage” in a single snapshot.5 It can also be operated in spiral mode using 64-detector elements for extended volume coverage. For dedicated cardiac CT angiography, we routinely perform a volume acquisition with coverage from carina to cardiac apex. Prospective ECG-triggering with an acquisition window from 70% to 100% of the RR interval is used in patients with heart rates ⬍65 bpm and 35%-100% for heart rates ⬎65 bpm.5 Retrospective ECG-gating is used for functional analysis whereby cine loops can be reconstructed for dynamic visualization of valvular function and calculation of left ventricular functional parameters. Coronary CT angiography is emerging as a valid alternative to cardiac catheterization in selected patient groups and as it also provides extraluminal
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information is especially useful for visualizing tortuous or anomalous vascular anatomy. The main drawback of MDCT is its attendant radiation burden, especially for coverage of the entire thorax, although dose reduction strategies such as ECG-gated current modulation continue to evolve.6 Although ECG-gating improves confidence in assessment, many of the lesions presented in this article may be readily appreciated on nongated acquisitions.
Left Ventricle Aneurysm Left ventricular aneurysm is defined as a distinct area of abnormal left ventricular diastolic contour with systolic dyskinesia or paradoxical bulging.7 True left ventricular aneurysms involve the full thickness of the left ventricular wall, while a false aneurysm represents a localized rupture contained by pericardial adhesions. The vast majority of aneurysms relate to coronary artery disease with a small proportion caused by trauma, sarcoidosis, or other form of cardiomyopathy.7 The incidence of true left ventricular aneurysms in patients with prior myocardial infarction may be as high as 10%-25%, although this is probably in decline with the increased use of thrombolytics and primary revascularization.8 False aneurysms result from ventricular rupture, which typically occurs 5-10 days following myocardial infarction. Ventricular aneurysms diminish systolic and diastolic function, increase myocardial oxygen demand, and decrease cardiac output because of volume loading.8 Untreated, the natural history of true and false aneurysms is progressive enlargement with its attendant complications. False aneurysms are associated with a much higher risk of free rupture and sudden death and operative repair is generally advocated; true aneurysms are more often managed medically with or without concomitant revascularization.8 Other recognized complications include in situ thrombosis with systemic embolization, ventricular arrhythmias, and stretching of the mitral valve leading to regurgitation. Several imaging features help differentiate a true from false aneurysm. False aneurysms usually have a mouth that is considerably smaller than the maximal aneurysmal diameter and most often occur in the circumflex coronary artery territory, ie, along the inferolateral wall (Fig 1). Also, a recent article has suggested that diffuse pericardial enhancement as
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FIG 1. False aneurysm of the left ventricle in a 76-year-old man with a prior history of circumflex coronary artery territory infarction. (A) Axial CT image. The aneurysm has a narrow neck from the left ventricle (LV) and is contained by pericardium (arrows). It contains partially calcified mural thrombus (*). (B) Volume-rendered 3-dimensional reconstruction showing the same with margins of the aneurysm marked by arrows. LV ⫽ left ventricle; LA ⫽ left atrium. (Color version of figure is available online.)
assessed by CMR may be a characteristic feature of false aneurysms.9 Up to 90% of true aneurysms result from full-thickness infarction in the left anterior descending coronary artery territory and they therefore predominate along the anterior wall and apex (Fig 2).8
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FIG 2. True aneurysm of the left ventricle in a 65-year-old man with a prior history of left anterior descending coronary artery territory infarction. (A) Four-chamber SSFP CMR image in systole showing paradoxical “bulging” of the left ventricular apex (arrows). (B) Fourchamber T1-weighted delayed enhancement CMR image acquired 10 minutes following administration of gadolinium-based contrast agent and with an inversion recovery pulse sequence to null signal from normal myocardium. There is full-thickness enhancement at the apex in keeping with transmural infarction (arrows); in addition, there is low-signal mural thrombus (arrowhead). LV ⫽ left ventricle.
Some nonischemic left ventricular aneurysms have fairly characteristic CMR/MDCT features, particularly those in association with hypertrophic cardiomyopathy (HCM). HCM can predominantly involve the middle
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third of the left ventricle and is associated with formation of an apical aneurysm that is thought to result from generation of increased midventricular systolic pressures, so-called “burnt out apex.”10 A similar appearance is also recognized in apical variant HCM and has been attributed to longstanding smallvessel ischemia.10 Supportive imaging features for HCM include cavity obliteration in systole and patchy midwall delayed gadolinium enhancement. Takotsubo cardiomyopathy, also known as transient apical ballooning syndrome, is another form of nonischemic cardiomyopathy associated with aneurysmal left ventricular dilatation. It is postulated to be caused by high circulating catecholamine levels as may occur at times of severe emotional stress and typically presents with chest pain and ECG changes suggestive of anterior wall myocardial infarction.11 Its imaging hallmark is apical dyskinesia with preserved or hypercontractile basal function and the coronary arteries are nonobstructed.12 CMR shows no signs of infarction or infiltration and left ventricular function usually fully recovers with normalization by 2-3 months.12 Left ventricular mural thrombus occurs in up to 40% of patients with a dyskinetic ventricular segment. On CMR signal intensity of thrombus varies with age on T1- and T2-weighted images and delayed gadolinium enhancement images are most helpful for making a confident diagnosis whereby thrombus appears of low signal compared with adjacent tissues4 (Fig 2B). On MDCT thrombus appears as a laminated lowattenuation lesion abutting the often thinned myocardium (Fig 1A).
Diverticulum Left ventricular diverticulum is an outpouching that has walls composed of predominantly myocardial tissue and involves at least half of the compacted myocardial wall thickness.13 The reported prevalence is 0.3%-2% with diverticula described in the literature ranging in size from 0.5 to 8 cm.8 The majority are thought to be congenital in nature and they are usually asymptomatic, being discovered incidentally during diagnostic imaging procedures performed for other reasons.13 There is a postulated association with ventricular arrhythmias and cardioembolic embolism but no direct link has been established. MDCT affords the highest spatial resolution of the noninvasive imaging modalities and ventricular diverticula are increasingly reported as ancillary findings in
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FIG 3. Left ventricular diverticulum as an incidental finding in a 55-year-old man undergoing CMR for assessment of myocardial ischemia. (A) Four-chamber SSFP CMR image showing a diverticulum involving the distal portion of the interventricular septum (arrow). (B) Short-axis SSFP CMR image showing the same (arrows). LV ⫽ left ventricle.
patients undergoing ECG-gated coronary CT angiography.13 They are most commonly found at the apex and perivalvular areas, although they have been reported in nearly all regions. Ventricular diverticula are occasional findings on CMR studies (Fig 3).
Right Ventricle Right ventricular aneurysm is unusual as it is the left coronary circulation that more often undergoes infarction; a 0.08% incidence has been reported following myocardial infarction.14 Other causes include trauma and arrthymogenic right ventricular cardiomyopathy (ARVC). ARVC is a disease complex characterized by
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FIG 4. Focal dyskinetic segment of the right ventricular free wall in a 36-year-old woman with a diagnosis of ARVC. Axial SSFP CMR image in systole showing a focal dyskinetic segment of the right ventricular free wall (arrow).
gradual loss of right ventricular myocytes and replacement by adipose and fibrous tissue with subsequent dilatation, dysfunction, and potential for electrical instability.15 The latter predisposes to ventricular arrhythmias and sudden death, most often in young adults. ARVC has an estimated incidence of 1 in 5000 of whom around 50% will have a positive family history.16 Diagnosis relies on a combined assessment of clinical, genetic, histologic, and imaging-based abnormalities. CMR is the imaging modality of choice with the most sensitive markers of ARVC being right ventricular systolic dysfunction (right ventricular ejection fraction ⬍50%) and regional wall motion abnormality, which may constitute a focal dyskinetic (aneurysmal) segment (Fig 4).15 The inflow, outflow, and apical portions of the right ventricle are most often affected, the so-called “triangle of dysplasia.” The identification of macroscopic intramyocardial fat adds confidence to making the diagnosis but will only be visible in around 60% of cases.17 ECG-gated MDCT is an alternative to CMR in patients who are precluded from undergoing MRI examination (Fig 5).15
Left Atrium Aneurysm The left atrium normally measures less than 4.5 cm in anteroposterior dimension and is considered aneurysmal when its diameter exceeds 6 cm.18 There are many causes of left atrial enlargement but it most
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FIG 5. Fatty infiltration of the right ventricular free wall in a 25-year-old woman with a presumptive clinical diagnosis of ARVC. Axial MDCT image showing macroscopic fat deposition (arrows). RV ⫽ right ventricle. (Color version of figure is available online.)
frequently occurs secondary to ischemic cardiomyopathy whereby the left ventricle dilates, causing distortion of the mitral subvalvular apparatus with resultant mitral regurgitation.19 Mitral stenosis is another frequent cause of left atrial enlargement, most commonly occurring as a late sequelae of rheumatic heart disease. CMR is the modality of choice for assessing left ventricular function, while dynamic perfusion and delayed gadolinium enhancement sequences permit assessment of ischemia and infarction, respectively.19 Ischemic left ventricular dysfunction results in cavity dilatation (diastolic dimension ⬎5.5 cm) and wall thinning, which are readily appreciated. Hallmark imaging features of mitral stenosis are thickening and retraction of the valve leaflets and chordae tendinae in association with left atrial enlargement (Fig 6).20 MDCT and CMR can also be used to assess mitral stenosis severity by planimetry of the orifice opening area, whereby a diastolic area less than 2 cm2 is considered clinically significant.20
Diverticulum Left atrial diverticula are highly prevalent, being reported in 15%-25% of all ECG-gated cardiac CT examinations.21 They are thought to represent anatomical variants rather than pathologic findings and in the
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FIG 6. Rheumatic mitral stenosis with gross biatrial enlargement in a 31-year-old woman with rheumatic mitral stenosis. Axial MDCT image showing pronounced thickening of the posterior mitral valve leaflet (arrow). LA ⫽ left atrium; RA ⫽ right atrium.
FIG 7. Left atrial diverticulum as an incidental finding in a 55-year-old woman undergoing cardiac CT angiography for investigation of chest pain. Axial MDCT image showing characteristic location and appearances (arrow). LA ⫽ left atrium; Ao ⫽ aortic root.
majority of instances are not associated with other congenital cardiac anomalies.21 What role they may have in the development of atrial fibrillation or an increased prevalence of thromboembolic disease remains the subject of ongoing debate. An atrial diverticulum is recognized by its “saclike” shape, broad-based ostium, and smooth wall contour. The majority measure between 3 and 10 mm in maximal dimension and are most often located in a superior anterior location (Fig 7).21 An accessory left atrial appendage can have a similar appearance but its wall contour is typically irregular, owing to the presence of fine pectinate muscles, and they are more frequently found in an inferior left lateral location.21
pid valve leaflet with resultant “atrialization” of the right ventricle (Fig 8).23 Other causes of right atrial enlargement include pulmonary valve stenosis or regurgitation and any cause of pulmonary arterial hypertension including left to right shunts. Right atrial enlargement can cause palpitations and atrial arrhythmias.23 CMR is the modality of choice for assessment of the tricuspid valve, right heart chambers, and any associated congenital cardiac anomalies; however, ECG-gated cardiac MDCT has an emerging role in those patients in whom CMR is contraindicated.
Right Atrium Aneurysm The right atrium normally measures less than 3.5 cm in transverse dimension and is considered aneurysmal when its diameter exceeds 5.5 cm.22 There are a wide range of conditions that may be associated with right atrial enlargement, including primary disorders of the tricuspid valve such as Ebstein’s anomaly in which there is apical displacement of the septal tricus-
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Diverticulum Right atrial diverticulum is a thin-walled outpouching from the right atrial free wall that histologically consists of fibrous tissue and intima and lacks a muscular component that distinguishes it from right atrial aneurysm.24 The etiology remains incompletely understood and many cases probably remain subclinical. Large diverticula have the potential to rupture, develop in situ thrombosis, and cause symptomatic compression of the right ventricle. A recent review of reported cases indicated a 6% risk of sudden cardiac death and concluded that surgical resection should be performed in those who become symptomatic.23 Both CMR and MDCT can be used to confirm the diagnosis
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FIG 8. Ebstein’s anomaly in a 28-year-old man in whom CMR evaluation was precluded by claustrophobia. Axial MDCT imaging showing displacement of the tricuspid valve leaflets (arrows) deep into the “atrialized” right ventricle. RA ⫽ right atrium; RV ⫽ right ventricle.
whereby the diverticulum communicates via a narrow opening that can be solitary or fenestrated (Fig 9).
Interatrial Septum Excessive mobility of the interatrial septum or membranous portion of the interventricular septum is termed cardiac septal aneurysm when the protrusion extends ⬎10 mm beyond the septal plane.25 The prevalence is reported as 0.2%-3% in the general population and there is an association with patent foramen ovale with consequent right to left shunting and increased risk of stroke, which may be as high as 3.8% per annum.26 Septal aneurysm is best appreciated on review of cine sequences from ECG-gated MDCT or CMR examinations, which can clearly depict dynamic septal bowing (Fig 10). Dynamic contrast-enhanced CMR and more recently ECG-gated MDCT, using a saline flush, have been shown as accurate means of patent foramen ovale detection.27
Aortic Root The sinuses of Valsalva (SOV) are 3 focal expansions that form the walls of the aortic root. They give rise to
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FIG 9. Right atrial diverticulum in a 52-year-old man who presented with chest pain. (A) Chest x-ray showing “bulging” right heart border (arrows). (B) Axial SSFP CMR image showing large blood-filled cavity compressing the right ventricle (*) and a small pericardial effusion. (C) Axial SSFP CMR image showing multiple fenestrated openings (arrows) between the right atrial free wall and the diverticulum (*). Also, note the small pericardial effusion. RA ⫽ right atrium.
Curr Probl Diagn Radiol, March/April 2011
FIG 10. Atrial septal aneurysm in a 66-year-old man with a prior history of myocardial infarction. Four-chamber SSFP CMR image showing pronounced “bowing” of the interatrial septum into the right atrium (arrows). LA ⫽ left atrium.
the right and left coronary artery ostia (with the exception of the noncoronary sinus) and function as a support structure for the aortic valve.28 The aortic root can be focally or globally dilated. Focal dilation or 1 or 2 sinuses is classified as SOV aneurysm, whereas dilation of all 3 sinuses is classified as aortic root aneurysm.29 SOV aneurysms are rare anomalies with an estimated prevalence of 0.17%.29 The majority are congenital, resulting from a deficiency of elastic lamellae in the sinus wall, which gradually gives way under high-pressure flow, leading to progressive aneurysmal dilatation and eventually rupture.30 Unruptured aneurysms are usually clinically silent and most are discovered serendipitously on echocardiography performed for another indication.31 Rupture often presents dramatically with sudden hemodynamic collapse but can have a more insidious onset depending on its site and size.30 Aneurysms most commonly originate from the right coronary sinus (80%); less commonly from the noncoronary sinus (15%), and rarely from the left sinus (5%).29 TTE is the modality of choice in the setting of suspected acute SOV rupture; however, MDCT and CMR are being increasingly used in the nonemergent setting to delineate anatomy and relationship to surrounding structures. Owing to its high spatial resolution, ECG-gated MDCT is an excellent means of assessment with SOV aneurysm appearing as a thinwalled crescent-shaped outpouching (Fig 11).32 The
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FIG 11. Sinus of Valsalva aneurysm in a 36-year-old man who presented acutely with chest pain and dyspnea. Axial MDCT image showing a large crescent-shaped structure that extends deep into the left atrium (arrows). Also, note bilateral pleural effusions secondary to decompensation from aorto-left atrial fistula, which was confirmed at surgery. LA ⫽ left atrium; LV ⫽ left ventricle.
principle advantages of CMR are its ability to quantify any associated aortic regurgitation and, in the setting of chronic rupture, into the right heart chambers when shunt fraction can be estimated using phase-contrast imaging performed through the proximal aorta and pulmonary artery. Aortic root aneurysm is commonly caused by conditions associated with annulo-aortic ectasia such as Marfan syndrome and other connective tissue disorders.33 Annulo-aortic ectasia is characterized by progressive enlargement of all 3 sinuses in conjunction with effacement of the sinotubular junction to give a “tulip bulb” appearance (Fig 12).29 Stretching of the aortic valve apparatus invariably leads to aortic regurgitation and left ventricular volume overload. Aortic root dimensions are best measured in a coronal oblique plane to achieve reproducible results; maximal SOV dimension should not exceed 4 cm in a male and 3.6 cm in a female.34
Main Pulmonary Artery The main pulmonary artery (MPA) is dilated when its maximal diameter exceeds 3 cm and its left and
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FIG 12. Aneurysm of the aortic root and ascending thoracic aorta in a 38-year-old man with Marfan syndrome. (A) Axial black blood prepared CMR image showing pronounced dilatation of the aortic root. (B) Volume-rendered 3-dimensional magnetic resonance angiogram image showing fusiform dilatation of the aortic root and ascending aorta with loss of the normal “waisting” at the sinotubular junction. Ao ⫽ aorta.
right main branches normally measure ⬍2 cm in an adult.35 The MPA can become aneurysmal secondary to longstanding pulmonary arterial hypertension of which the causes are diverse and include chronic thromboembolic disease, left to right shunts, and smallvessel vasculopathies.36 Several congenital defects associated with pulmonary valve stenosis may cause the pulmonary artery to become aneurismal, including tetralogy of Fallot. MPA dimension is conventionally measured at its bifurcation in the axial plane.36 MDCT pulmonary angiography is fast becoming the reference technique for assessment of pulmonary arterial hypertension in which partially calcified laminated “in situ” thrombus
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FIG 13. Aneurysmal dilatation of the main pulmonary artery in a 52-year-old woman with untreated ostium secundum type atrial septal defect. (A) Axial black blood prepared CMR image showing pronounced dilatation of the main pulmonary artery (5 cm maximal transverse diameter). (B) Volume-rendered 3-dimensional magnetic resonance angiogram image showing gross dilatation of the main pulmonary artery and proximal branches. PA ⫽ pulmonary artery.
is often seen lining the proximal pulmonary artery branches. CMR is the reference technique for assessment of congenital heart disease and pulmonary valve stenosis severity can be quantified using phase-contrast sequences. In addition, magnetic resonance angiography can be used to make assessment of the proximal pulmonary vasculature (Fig 13).
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ital in origin and most often originate from the right coronary artery with drainage to the right-sided cardiac chambers or pulmonary artery (Fig 15). With catheter coronary angiography, only intraluminal flow can be evaluated, and no information is provided about the vessel wall; thus, the true size of an aneurysm may be underestimated and in some cases an aneurysm may not even be seen when it is occluded or contains a substantial amount of thrombus.42 MDCT coronary angiography is an excellent means of assessing anomalous course and termination of coronary vessels and the extraluminal information that it provides is particularly useful for evaluating aneurysms. Coronary aneuryms are occasional findings on CMR studies and should not be confused with an extracardiac mass (Fig 16).4
FIG 14. Coronary artery aneurysm in a 24-year-old man with a history of Kawasaki disease in childhood for which he required coronary artery bypass grafting. Axial MDCT image showing an aneurysm of the left anterior descending coronary artery, which contains extensive partially calcified mural thrombus (arrows). Ao ⫽ aorta.
Coronary Arteries A coronary artery aneurysm is when the maximal diameter of a coronary vessel is increased by 1.5 times the normal diameter with involvement of less than 50% of the vessel length.37 The reported frequency is 0.3%-5% from post mortem studies.38 Atherosclerosis is by far the commonest cause and is thought to predispose to aneurysmal dilatation via turbulent flow and increased wall stress.39 Less common causes include coronary artery fistulas and vasculitides such as Takayasu arteritis and Kawasaki disease. Kawasaki disease is an acute self-limited multisystemic panarteritis that is most prevalent in Japan.40 Coronary artery aneurysms have been reported in 15%-25% of untreated cases and may be complicated by in situ thrombosis with arterial stenosis or occlusion (Fig 14).40 Takayasu arteritis is a large-vessel vasculitis more frequently seen in young women that is characterized by disruption of elastic fibers with marked thinning of the tunica media.41 It has a predilection for the great vessels but coronary involvement is reported in 10%15% of cases.41 A coronary artery fistula is defined as a connection between a coronary artery and a cardiac chamber or great vessel, with the connection bypassing the myocardial capillary bed.42 Most fistulas are congen-
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Coronary Veins and Bypass Grafts The coronary sinus is a channel through which the epicardial veins drain to the right atrium. Coronary sinus aneurysms or diverticulae are venous outpouchings located within the epicardial layers of the posterior ventricular septum. They are associated with accessory conduction pathways and supraventricular reentrant tachycardia.43 The coronary sinus may also be enlarged in association with congenital anomalies such as persistent left-sided superior vena cava and coronary sinus atrial septal defect (a defect in the sinus roof that permits interatrial shunting). Both MDCT and CMR can depict enlargement of the sinus and any associated structural abnormalities. Saphenous vein graft pseudoaneurysm is a wellrecognized late complication of coronary artery bypass grafting and has been attributed to vascular trauma at time of harvesting or implantation.44 The proximal graft anastomotic site is most commonly affected (Fig 17). Large aneurysms may be first detected on routine chest x-ray as patients not infrequently remain symptom free.45 MDCT is the modality of choice for further assessment and typically reveals a well-circumscribed mass with partial or complete contrast medium enhancement depending on the degree of intimal thrombosis.45 Treatment options include surgical resection, coil embolization, or a conservative approach, especially in patients who are asymptomatic.
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FIG 16. Right coronary artery aneurysm in a 50-year-old man in whom a right ventricular mass was identified on echocardiography. Axial SSFP CMR image showing a smoothly marginated mass indenting the right ventricular free wall (arrows).
FIG 17. Saphenous vein graft aneurysm in a 68-year-old man. Axial MDCT image showing dilatation of the graft at its origin from the ascending thoracic aorta (arrows). Ao ⫽ aorta.
4™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™™ FIG 15. Left coronary artery to pulmonary artery fistula in a 44-year-old man undergoing cardiac MDCT for investigation of chest pain. (A) Axial MDCT image at the level of the aortic root showing several tortuous dilated vessels (arrows) that were arising from the left anterior descending coronary artery. (B) Axial MDCT image at the level of the pulmonary artery showing fistulous communication and a focal aneurysm (arrows). (C) Volume-rendered 3-dimensional reconstruction showing the fistulous vessels coursing anterior to the pulmonary artery. Ao ⫽ aorta; PA ⫽ pulmonary artery. (Color version of figure is available online.)
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Conclusions Advances in MRI and MDCT have made them attractive tools for cardiac morphologic assessment. Highresolution images can be routinely acquired, enabling accurate characterization of any anatomical derangement and its sequelae. Familiarity with the characteristic imaging features of cardiac aneurysms and diverticulae will help expediate their diagnosis.
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