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Case 10 - Ventricular non-compaction
- from Section 1 - Cardiac pseudotumors and other challenging diagnoses
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- By Nathan Johnson, United Imaging Consultants, Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 34-37
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Summary
Imaging description
Non-compaction of the ventricular myocardium is a rare congenital cardiac disease characterized by excessive myocardial trabeculations and deep intertrabecular recesses. Non- compaction is thought to be the result of the arrest of normal cardiac development in utero during the 5th to 8th week of life, a time when loose myocardial fibers in the ventricles become organized and “compacted.” [1] Non-compaction has been most often described in the left ventricle, but biventricular and isolated right ventricular involvement has also been reported. The most common locations for non-compaction are the left ventricular apex, lateral wall, and inferior wall (Figure 10.1). Diagnostic criteria have been proposed for echocardiography that rely upon a comparison of the thickness of trabeculated and compacted myocardium, or the number of prominent trabeculations. By MRI, non-compaction has been defined as a ratio of trabeculated to compacted myocardium of greater than 2.3 in end-diastole. However, recent studies in both normal subjects and patients with heart failure have suggested that current MRI criteria may be overly sensitive, resulting in overdiagnosis. Patients with non-compaction cardiomyopathy will often have myocardial dysfunction manifested by reduced ventricular ejection fraction and cavity dilation, sometimes complicated by intracavitary thrombus (Figure 10.2), which may aid in diagnosis. On dark blood images, high signal may be seen in between the prominent trabeculations due to slow blood flow. Delayed myocardial enhancement involving the prominent trabeculations may be present and has been associated with reduced ejection fraction and more advanced disease.
Importance
Accurate diagnoses of LV non-compaction is challenging due to lack of clear diagnostic test for the disease and substantial overlap of current criteria with healthy subjects and those with heart failure from different causes. True non-compaction cardiomyopathy is a serious disease with a poor prognosis. Identification of these patients is important as they have a high rate of symptomatic heart failure, thromboembolic events, ventricular arrhythmias, and sudden death. Some will eventually require heart transplant or placement of an implantable cardioverter defibrillator (ICD).
Case 38 - Giant coronary artery aneurysms
- from Section 4 - Coronary arteries
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- By Mark Stellingworth, University of South Carolina Medical School, Saurabh Jha, Hospital of the University of Pennsylvania, Koteswara Pothineni, Louisiana State University School of Medicine, Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 120-123
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Summary
Imaging description
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).
Importance
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.
List of contributors
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp viii-viii
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Case 11 - Hypertrophic cardiomyopathy mimics
- from Section 1 - Cardiac pseudotumors and other challenging diagnoses
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- By Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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Summary
Imaging description
Hypertrophic cardiomyopathy (HCM) is a diagnosis made when myocardial wall thickness exceeds 15 mm in the absence of any explanatory cardiac disease. Importantly, there are several uncommon reasons for cardiac hypertrophy that can mimic the appearance of HCM and should be considered whenever making the diagnosis. One such entity is cardiac amyloidosis. Cardiac amyloidosis is notable for concentric left and right ventricular hypertrophy in combination with diastolic dysfunction, features that overlap with HCM. Unlike the majority of HCM cases, however, hypertrophy in amyloid is diffuse and symmetric (Figure 11.1). Amyloid also has a characteristic pattern of late gadolinium enhancement (LGE), which is diffuse, concentric, and subendocardial, unlike the patch distribution of LGE seen in HCM (Figure 11.1). In addition, amyloid causes alterations in the kinetics and distribution of gadolinium contrast, which results in poor differentiation between the myocardium and blood pool on LGE images due to absorption of gadolinium by amyloid proteins in both the blood and heart. A second major diagnostic consideration when evaluating for HCM is a metabolic disorder such as Anderson-Fabry disease or, less commonly, Danon disease (Figure 11.2). These patients are typically young with left ventricular hypertrophy, similar to HCM, and midwall LGE, often confined to the basal inferolateral wall.
Importance
Mimics of HCM are important to recognize given that their treatment and prognosis significantly differ from that of HCM. Referring clinicians should be made aware of the possibility of alternative diagnoses so that additional testing is ordered.
Typical clinical scenario
Mimics of HCM are less common than HCM itself. Amyloidosis is uncommon, affecting 10 per million person years in the United States. The heart is involved in 90% of patients with systemic AL, or primary, amyloidosis, the most common of several types of amyloidosis. More than half of patients will die from arrhythmia or heart failure. Anderson-Fabry disease is the most common of the metabolic syndromes that result in myocardial hypertrophy. It is an x-linked disorder that is found in approximately 1:40,000 males; females are rarely affected.
Case 70 - Pseudodissection due to aortic graft kinking
- from Section 8 - Post-operative aorta
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- By Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 224-226
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Summary
Imaging description
Prosthetic aortic grafts often have areas of kinking where there is in-folding of the graft wall into the aortic lumen. This is a normal post-operative finding that is generally of no clinical consequence. On axial images, vertically oriented folds will have the appearance of an intraluminal flap and can mimic dissection (Figures 70.1 and 70.2). Inspection of sagittal and coronal planes and volume-rendered images will allow visualization of the kinked segment and exclusion of dissection.
Importance
It is important to avoid misdiagnosis of aortic dissection as it may lead to unnecessary surgery or repeat imaging.
Typical clinical scenario
Kinking in the aortic graft is common in patients with prior open graft repair of the thoracic or abdominal aorta.
Differential diagnosis
Aortic graft kinking should be distinguished from a true aortic dissection. Careful inspection of multiplanar and 3D reformatted images should allow visualization of the kinking and prevent misdiagnosis. The location of abnormality can also be helpful as dissections do not occur within prosthetic aortic graft material. Dissections may, however, occur in the native aorta immediately adjacent to an anastomosis.
Teaching point
Kinking of aortic grafts after open aortic repair is common and can result in linear intraluminal filling defects that mimic dissection on axial images. The use of multiplanar reformatted and volume-rendered images will allow visualization of the kinked segment and help avoid misdiagnosis.
Case 35 - Myocardial bridging
- from Section 4 - Coronary arteries
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- By Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 109-112
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Summary
Imaging description
In myocardial bridging, the epicardial coronary arteries, normally surrounded by fat, dive inferiorly and course through myocardial tissue before exiting distally back into the epicardial fat. Myocardial bridging can range in length from a few millimeters to several centimeters and be of variable depth, typically between 1–4 mm. Bridged segments are recognized on coronary CT when the coronary arteries are circumferentially surrounded by myocardial tissue (Figure 35.1). The left anterior descending coronary artery is the most commonly involved; however, the circumflex and right coronary arteries may also have bridged segments (Figure 35.2). If multiphase images are acquired, narrowing of the intramyocardial segment may be seen during systole as the myocardium contracts. On catheter angiography, this is referred to as the “milking effect” and is the classic finding for the diagnosis of myocardial bridging. In patients with coronary artery disease, atherosclerosis will spare the bridged segment, with plaques typically developing proximal to the segment of bridging (Figure 35.3).
Importance
In the vast majority of cases, myocardial bridging is a benign finding incidentally encountered at cardiac imaging of no clinical consequence. Some studies have associated long and deep myocardial bridges with the presence of ischemia. Intramyocardial segments have been rarely associated with cardiac events such as myocardial infarction or sudden death in small series and case reports. Based upon long-term follow-up studies of patients diagnosed by catheter angiography, the prognosis for patients with myocardial bridging diagnosed with bridging by catheter is very good. Although large cohort studies are lacking, in two studies of patients with bridging identified by coronary CT, 31/74 and 117/334 had bridged segments; however, there was no association between presence of bridging and adverse cardiac events after several years of follow-up.
Typical clinical scenario
Myocardial bridging is frequently encountered at coronary CT.
Case 2 - Cardiac pseudotumor due to lipomatous hypertrophy of the interatrial septum
- from Section 1 - Cardiac pseudotumors and other challenging diagnoses
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- By Pejman Motarjem, Desert Radiologists, Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 4-7
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Summary
Imaging description
Lipomatous hypertrophy of the interatrial septum (LHIS) is a benign process of the heart characterized by fatty infiltration of the interatrial septum. The diagnosis is made when fat in the interatrial septum measures greater than 20 mm in thickness and it is usually an incidental finding at cardiac imaging.
At echocardiography, LHIS is recognized by echogenic thickening of the interatrial septum. On multiple detector computed tomography (MDCT) (with or without contrast) LHIS is a low-attenuation, < 0 Hounsfield units, bilobed mass with smooth margins that spares the fossa ovalis. It is this sparing of the fossa ovalis which gives this entity its characteristic bilobed or dumbbell-shaped morphology (Figure 2.1). Often, there is cranial extension to the level of the cavoatrial junction and fat may surround the distal superior vena cava (Figure 2.2).
On MRI the morphology of LHIS is similar to MDCT. The LHIS demonstrates hyperintensity on T1-weighted imaging with homogenous signal drop out on a fat-suppressed T1 sequence characteristic of macroscopic fat (Figure 2.2). On post-gadolinium sequences no enhancement is seen.
FDG uptake within the atrial septum at positron emission tomography (PET) examinations may be seen, and is attributed to the variable presence of brown fat within LHIS (Figure 2.3). It is important to note that the benign FDG uptake in LHIS must not be mistaken for a malignant process such adenopathy or metastatic tumor. Fusion PET-CT will help localize radiotracer uptake to the atrial septum and differentiate it from surrounding structures such as the right hilum, pleura or mediastinum. In difficult cases, it may be necessary to correlate PET-CT findings with either MRI or MDCT in order to prevent inappropriate staging of the patient.
Importance
The condition of LHIS is a benign incidental finding and typically does not cause any symptoms. Since it may demonstrate increased FDG uptake on PET/CT, it must not be confused with a malignant process, leading to misdiagnosis, inappropriate follow-up imaging or inappropriate biopsy.
Case 85 - Superficial femoral artery occlusions
- from Section 10 - Peripheral vascular
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- By Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 263-265
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Summary
Imaging description
Superficial femoral artery (SFA) occlusions may be missed in at least two scenarios at cross-sectional imaging. On standard abdominopelvic CT examinations, the SFAs are often only visualized on the last few slices obtained. In our experience, it is not uncommon for SFA occlusions to go unnoticed, particularly in patients with extensive atherosclerotic disease, given that they are an “edge of the film” finding and may not be included in the typical radiologist search pattern (Figure 85.1). The other scenario where SFA occlusions may be missed occurs with MRA examinations of the lower extremity. Symmetric bilateral occlusions may be difficult to appreciate on coronal maximum intensity projection (MIP) images of the lower extremities, given extensive collateral vascularity from the deep femoral arteries (Figures 85.2 and 85.3). In addition, SFA occlusions often begin at the origin of the vessel and continue for its entire length. In these cases, SFA occlusions must be recognized as the absence of a finding, i.e., the normal vessel, which can be challenging. The normal SFA should be recognized as a medially located vessel free from significant branches along its course through the thigh, unlike the deep femoral artery, which is located laterally and more posterior with numerous branches.
Importance
Occlusions of the SFA can be clinically important, potentially resulting in claudication symptoms, rest pain or, in extreme cases, tissue ischemia. SFA occlusions due to embolic phenomena are important to recognize as patients may require anti-coagulation or thrombectomy and additional imaging studies may be necessary to identify the source of the embolus.
Typical clinical scenario
SFA occlusions may be encountered incidentally in patients with extensive atherosclerotic disease or may be the primary finding in patients being evaluated for suspected peripheral arterial disease (PAD). The prevalence of PAD is approximately 12% in older adults.
Differential diagnosis
In patients with prior surgery for peripheral arterial disease, occlusions of grafts within the thigh may be mistaken for occlusion of the native vessel.
Case 5 - Pseudothrombus in the left ventricle due to microvascular obstruction
- from Section 1 - Cardiac pseudotumors and other challenging diagnoses
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- By Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 16-19
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Summary
Imaging description
A mass-like area of low signal intensity mimicking thrombus may be encountered in the setting of microvascular obstruction (MO) when cardiac MRI (CMR) is performed after acute myocardial infarction (MI). CMR is often used to assess viability after MI for prognosis and determining the need for possible revascularization. In the acute setting, large transmural MIs may demonstrate MO, which has been associated with poorer outcomes and adverse left venticular (LV) remodeling at follow-up imaging. MO is subendocardial in location and low in signal intensity on late gadolinium enhancement (LGE) images, characteristically surrounded by a zone of increased myocardial signal intensity due to LGE (Figure 5.1). MO represents a densely infarcted area of no-flow within the myocardium where gadolinium cannot reach due to severe micro- vascular damage. MO is recognized by its association with a wall motion abnormality, subendocardial decreased perfusion on dynamic post-contrast images, and a rim of delayed enhancement representing a zone of infarcted tissue with intact microvasculature that surrounds the infarct core with MO.
Importance
MO is important to recognize given the fact that it is associated with poorer outcomes after MI. MO must be correctly differentiated from thrombus, as this may require additional treatment such as anticoagulation therapy, which will expose the patient to additional bleeding risk in the inappropriate setting.
Typical clinical scenario
MO is encountered when viability MRI scans are performed in someone with recent MI. Differentiation of thrombus from MO is important as these patients with hypofunctioning myocardium in the setting of recent MI are at risk for thrombus due to blood stasis.
Differential diagnosis
Thrombus is the most important entity on the differential diagnosis of MO. The location of MO within the wall of the myocardium can help differentiate MO from thrombus. Myocardial location can be clarified by direct comparison of LGE and precontrast images (Figures 5.1, 5.2).
Case 32 - Pseudostenosis in the coronary arteries due to motion artifact
- from Section 4 - Coronary arteries
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- By Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 102-104
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Summary
Imaging description
Motion artifact in coronary CT angiography (CCTA) occurs when the temporal resolution of the acquisition is inadequate to resolve moving cardiac structures. A temporal resolution of < 50 msec is required to permit imaging of cardiac structures during any point in the cardiac cycle without blurring. Current scanner technology has not yet achieved this benchmark, and therefore imaging is targeted to portions of the cardiac cycle that have the least motion, mid-diastole (60–70% of R-R interval) and end-systole (30–40% of R-R interval). Motion artifacts can affect any vessel, but are most pronounced in the RCA, the vessel with the highest displace- ment velocity and range during the cardiac cycle. Motion artifacts may have one of several appearances. In some cases, low-attenuation blurring of the coronary artery lumen and wall may be seen, simulating segmental high-grade stenosis or occlusion (Figure 32.1). In other cases, arcs or rounded regions of high and low attenuation may be seen adjacent to the coronary arteries (Figure 32.1). Recognition of blurring of the walls of cardiac chambers, such as the left atrium or ventricle, can provide a clue that the images are degraded by motion and should be interpreted with caution (Figure 32.1). In the setting of elevated heart rates (> 70 beats per minute), reconstructed phases obtained in end-systole at approximately 30–40% of the R-R interval have the greatest chance of diagnostic images. For motion-degraded CCTA examinations, multiple reconstructed phases can often be used to piece together a comprehensive assessment of the coronary arteries. In this scenario, not all vessel segments will be best visualized on a single phase, but each segment is well visualized on at least one phase.
Importance
Motion blurring can simulate coronary artery stenosis. The motion leads to blurring of the coronary lumen and adjacent low-attenuation fat, resulting in an appearance mimicking high-grade stenosis. Reconstructed phases from different points in the cardiac cycle should be evaluated to confirm or disprove any significant coronary artery stenosis (Figure 32.2). Motion artifact is the major reason for non-diagnostic scans.
Case 3 - Cardiac pseudotumor due to caseous mitral annular calcification
- from Section 1 - Cardiac pseudotumors and other challenging diagnoses
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- By Stefan L. Zimmerman, Johns Hopkins University School of Medicine
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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Summary
Imaging description
At cardiac MRI (CMR), mitral annular calcification (MAC) is low in signal intensity on bright blood, T1- and T2-weighted images and can appear as a smooth, multilobulated mass or masses in the region of the atrioventricular groove (Figure 3.1). Caseous, also known as liquefactive, MAC is a rare variant that is typically a larger, rounded mass with central liquefactive necrosis, composed of calcium, inflammatory cells, and cholesterol. Given that calcification is not well depicted by MRI, MAC can be mistaken for a cardiac tumor. Caseous MAC can occasionally be large – up to several centimeters in size and may displace mitral valve leaflets, resulting in valvular dysfunction such as regurgitation or stenosis. On post-contrast images, there is occasionally a thin rim of enhancement due to fibrous tissue surrounding the calcification (Figure 3.2). If CT is available, MAC is easy to identify on non-contrast images due to presence of high attenuation calcification (Figure 3.1).
Importance
MAC at CMR can be mistaken for a cardiac tumor or other type of cardiac mass, leading to inappropriate additional testing as well as patient anxiety. Although benign, the presence of MAC is a marker of increased cardiovascular risk. MAC was associated with a 50% greater likelihood of cardio vascular events at follow-up in the Framingham Heart Study and predicted both increased all-cause and cardiovascular death.
Typical clinical scenario
MAC is a common disorder. In the Multi-Ethnic Study of Atherosclerosis, MAC was detected by CT in 9% of a cohort of 6814 subjects from age 45–8. Caseous MAC is more rare, affecting < 1% of subjects with MAC. MAC is often discovered incidentally at echocardiography, and usually requires no further imaging. However, if the diagnosis is uncertain, patients may be referred to advanced imaging with MRI or CT.
Differential diagnosis
MAC should be differentiated from a true cardiac tumor. Location in the mitral annulus, low T1 and T2 signal intensity, and lack of enhancement are distinguishing characteristics.
Case 58 - Pericardial recess mimicking traumatic aortic injury
- from Section 7 - Acute aorta and aortic aneurysms
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- By Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
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- 05 June 2015
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Summary
Imaging description
In some patients, fluid in the anterior portion of the superior aortic recess of the pericardium can extend cranially and abut the aortic arch and the arch branch vessel origins. In patients being evaluated for trauma with multidetector CT, this fluid may be mistaken for periaortic hematoma (Figure 58.1). However, unlike hemorrhage, fluid in a pericardial recess will measure simple fluid attenuation and will have sharp, well-defined borders. Pericardial fluid abuts the aorta and great vessels without an intervening fat plane. Patients with acute aortic injury and hematoma will have high-attenuation fluid next to the aorta and a contour abnormality or intimal flap within the aorta itself.
Importance
Misdiagnosis of traumatic aortic injury could lead to inappropriate invasive catheter angiography or surgery.
Typical clinical scenario
Fluid in the superior aortic recess is common and may be encountered in patients with or without an associated pericardial effusion.
Differential diagnosis
In the setting of trauma, fluid in the superior pericardial recess can mimic periaortic hemorrhage; however, these entities can usually be distinguished by attenuation measurements (Figure 58.2). Fluid collections in the superior aortic recess simulating lymphadenopathy or aortic dissection have also been described.
Teaching point
Fluid in the anterior portion of the superior aortic recess abutting the aortic arch can mimic periaortic hematoma. Measurement of fluid attenuation values and close inspection of the aorta for contour abnormalities or intimal injury will help avoid misdiagnosis.
Case 47 - Inappropriate inversion time selection for late gadolinium enhancement imaging
- from Section 6 - Cardiovascular MRI artifacts
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- By David Bonekamp, University Hospital Heidelberg, Stefan L. Zimmerman, Johns Hopkins Medical Centre
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 146-149
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Summary
Imaging description
Inappropriate selection of the inversion time (TI) in late gadolinium enhancement (LGE) cardiac MRI (CMR) examinations results in incomplete suppression of the myocardium. Most frequently encountered is the selection of a TI that is slightly too short, resulting in a subendocardial “ring of hypointensity” and a mid-myocardial zone of hyperintensity (Figures 47.1 and 47.2). These artifacts may mimic true mid-myocardial delayed enhancement that can be seen in pathologic conditions such as sarcoidosis or dilated cardiomyopathy (Figure 47.3). In a less commonly encountered clinical scenario, suppression of abnormal myocardium (amyloidosis is the prototypical example) will cause hypointensity of abnormal myocardium. This will result in the poor quality of delayed enhancement images that is a hallmark of patients with amyloidosis (Figure 47.4).
Importance
Two potential pitfalls result from incorrect inversion time selection. First, incorrect nulling of the myocardium reduces the conspicuity of true myocardial delayed enhancement, potentially hiding underlying pathology, resulting in a falsenegative result. Second, incomplete nulling due to a short inversion time, if not recognized as artifact, can be erroneously interpreted as diffuse mid-myocardial LGE, leading to a falsepositive result. The interpreting radiologist must be familiar with the appearance of deviations of the TI selection, and be aware of underlying conditions, particularly amyloidosis, that can cause difficulty in selecting the correct TI time.
Typical clinical scenario
TI is selected to provide maximal contrast between normal and abnormal myocardium by completely nulling any signal from normal myocardium. TI selection determines the sensitivity for the detection of myocardial damage. The actual TI time needed for normal myocardial suppression depends on multiple factors, including the time after contrast injection, renal elimination of contrast, patient size, cardiac output, contrast dose and contrast agent. A typical approach for TI selection is the use of a “TI scout” sequence, which is typically an ECG-gated post-contrast sequence with images acquired at multiple delay times after an initial 180 degree inversion pulse, resulting in different TI contrasts throughout the cardiac cycle.
Case 50 - Aliasing artifact in phase-contrast cardiac MR
- from Section 6 - Cardiovascular MRI artifacts
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- By Stefan L. Zimmerman, Johns Hopkins Medical Centre
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
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- 05 June 2015
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Summary
Imaging description
Aliasing artifact occurs in phase-contrast MRI when the peak velocity of flowing blood being imaged exceeds the encoding velocity, or Venc. In phase-contrast MRI, specialized flowsensitive gradients are used to encode flow velocity and flow direction information into grayscale pixel values. The Venc is a parameter, expressed in cm/sec, that specifies the maximal velocity that can be measured by a given phase-contrast acquisition. The Venc is adjustable and is set at the MRI scanner before image aquisition. When the vessel being imaged contains flowing blood that is moving faster than the Venc, aliasing will occur. Pixels will become progressively brighter as velocities approach the Venc; however, pixels that represent velocities exceeding the Venc wrap around and are mapped to dark pixels from the opposite end of the grayscale spectrum (Figure 50.1). Depending on the direction of flow, the inverse situation can also occur, where white aliased pixels may be surrounded by dark non-aliased pixels with velocities just below the Venc (Figure 50.1).
Importance
Aliasing will result in inaccurate measurement of peak velocities within a vessel. Peak velocities are used to estimate the pressure gradient across a stenosis which can dictate treatment decisions. Automated flow measurement software can be used to correct for aliasing if peak velocity is less than three times the Venc. However, repeated acquisitions at an increased Venc setting are preferred for maximum measurement reliability.
Typical clinical scenario
Aliasing artifacts are seen whenever the flow velocity is greater than expected when setting the Venc. This is common in the setting of stenotic vessels or valvular stenosis. Elevated velocities may also be seen within the left ventricular outflow tract in the setting of obstructive hypertrophic cardiomyopathy. Typical maximal velocities for ascending aorta, pulmonary artery, and systemic veins are less than 150 cm/sec, less than 100 cm/sec, and less than 50 cm/sec, respectively. In the setting of stenosis, maximal velocities may increase to 500–1000 cm/sec, and repeated acquisitions with incremental increases of Venc may be necessary to find the optimal Venc to prevent aliasing.
Case 18 - Aneurysm of the interatrial septum
- from Section 2 - Cardiac aneurysms and diverticula
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- By Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
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- 05 June 2015
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Summary
Imaging description
Atrial septal aneurysms (ASA) appear as a thin-walled, round or lobulated outpouching located at the fossa ovalis. They are formed by redundant tissue of the fossa ovalis that protrudes ≥ 10–15 mm beyond the plane of the interatrial septum with a base ≥ 15 mm in width (Figure 18.1). ASAs bulge into either the left or right atrium depending upon the prevailing atrial pressure gradient and often have a “to-and-fro” motion throughout the cardiac cycle (Figure 18.2). Signal characteristics on imaging match the adjacent left or right atrial blood pool (Figure 18.3). For instance, if the aneurysm is protruding into the left atrium, signal characteristics will match the right atrial blood pool, and vice versa. Diagnosis is straightforward with echocardiography and cardiac MRI, given the ability to visualize the characteristic motion of the ASA during the cardiac cycle (Figure 18.4). Diagnosis can be challenging on enhanced CT examinations of the chest that use a saline chaser following the contrast bolus. The right atrium is low attenuation in these cases due to the saline flush. ASAs directed into the left atrium will appear as hypoattenuating masses in the enhanced left atrial blood pool (Figure 18.5). Conversely, septal aneurysms directed into the right atrium could be mistaken for a right atrial mass on acquisitions timed for the pulmonary arteries. Injection protocols that utilize dilute contrast in the second phase of the injection for opacification of right-sided heart structures are helpful to avoid this pitfall. In addition, if available, multiphase ECG-gated images are helpful to visualize the characteristic motion of septal aneurysms.
Importance
ASAs may be incorrectly mistaken for cardiac tumors, particularly atrial myxomas, during enhanced CT of the chest. Misdiagnosis or uncertainty in diagnosis can lead to unnecessary follow-up examinations, patient anxiety, or worse, inappropriate surgery. ASAs generally have a benign course; however, patients with ASA have an increased prevalence of patent foramen ovale, present in 50–70% cases (Figure 18.1), and cerebral ischemic events (stroke or transient ischemic attack).
Case 52 - Pseudostenosis on time-of-flight magnetic resonance angiography
- from Section 6 - Cardiovascular MRI artifacts
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- By David Bonekamp, University Hospital Heidelberg, Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
- Published online:
- 05 June 2015
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- 21 May 2015, pp 165-167
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Summary
Imaging description
Time-of-flight (TOF) magnetic resonance angiography (MRA) images are prone to several artifacts that may suggest stenosis or occlusion of vascular segments. TOF MRA is based on the acquisition of 2D or 3D gradient echo images which are optimized to saturate protons in stationary tissues while maximizing flow-related enhancement from inflowing blood protons that enter the slice during the acquisition. Saturation bands are added to selectively null signal from venous or arterial blood that is flowing in the opposite direction of the vessel of interest. For example, if an image of the abdominal aorta is desired, a saturation band below the plane of interest is used to null inflowing venous blood from the inferior vena cava. Several well-known artifacts occur with TOF imaging. In-plane flow can result in pseudostenosis or artifactual occlusion because blood protons flowing within a vessel parallel to the imaging plane will become saturated during the acquisition (Figure 52.1). Slow-flowing blood may also become saturated before it reaches the end of the TOF slab, such that the distal vessel appears attenuated in luminal diameter and signal. Reversal of flow, which can occur due to retrograde filling with collateral arteries, will be undetectable with TOF techniques due to the use of saturation bands to suppress venous contamination (Figure 52.2). Susceptibility artifacts from surgical clips or adjacent hardware may attenuate the MR signal, and the gradient echo (GRE) sequences used for TOF are especially sensitive for this type of artifact. Finally, dephasing of protons that occurs due to turbulent flow at vessel bifurcations may mimic stenoses, while accelerated and turbulent flow at existing stenoses may lead to overestimation of the degree of stenosis.
Importance
TOF MRA is a widely used unenhanced MRA method. Knowledge of artifacts that may mimic vascular stenosis or occlusion is essential for accurate interpretation. Misinterpretation of the absence or presence of vascular stenosis or occlusion can lead to unnecessary intervention or surgery, or fail to diagnose a treatable cause for the patient's symptoms.
Section 8 - Post-operative aorta
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Pearls and Pitfalls in Cardiovascular Imaging
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Case 26 - Bicuspid aortic valve with raphe mimicking tricuspid valve
- from Section 3 - Anatomic variants and congenital lesions
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- By Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Pearls and Pitfalls in Cardiovascular Imaging
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- 05 June 2015
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- 21 May 2015, pp 84-86
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Summary
Imaging description
Bicuspid aortic valves are congenital malformations of the aortic valve that result in two functional aortic valve leaflets. In the majority of cases, the right and left aortic cusps are fused with a central raphe, or ridge, that is variable in size. On static images of the aortic valve acquired in diastole with either cardiac CT or MRI, a bicuspid valve with prominent raphe will have an appearance that mimics a tricuspid valve (Figure 26.1). However, dynamic images obtained during systole will reliably demonstrate the restricted motion of the fused valve and typical fish-mouth appearance of the aortic valve orifice using either modality. Bicuspid valves are also typically morphologically abnormal with leaflet thickening and calcification commonly identified, that can suggest further investigation (Figure 26.2). Fusion occurs between the left and right cusps in the majority of patients.
Importance
Recognition of a bicuspid valve is important given the increased risk of aortic stenosis, regurgitation, aneurysm, and dissection. Patients with bicuspid valve are closely followed with serial echocardiography to assess valve and ventricular function.
Typical clinical scenario
Bicuspid aortic valve is the most common congenital cardiovascular abnormality, affecting 1–2% of the population. Bicuspid valve morphology is highly variable; however, fusion of the right and left cusps with a midline raphe is the most common pattern, found in 59% of cases in one large series. Patients with bicuspid valve may be referred to cardiac CT or MRI for assessment of coronary arteries, ventricular function, or aortic size. Bicuspid valves may also be an incidental finding on cardiac imaging exams performed for other indications.
Differential diagnosis
Tricuspid aortic valve with acquired cusp fusion due to senile degeneration can be difficult to distinguish from congenitally bicuspid aortic valve with raphe given similar morphologies. Central calcification of the midline raphe, unequal cusp size, and the presence of an ascending aortic aneurysm are more commonly associated with bicuspid valves and can suggest the diagnosis.
Case 57 - Ductus diverticulum mimicking ductus arteriosus aneurysm
- from Section 7 - Acute aorta and aortic aneurysms
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- By Pejman Motarjem, Diagnostic Radiologist, Stefan L. Zimmerman, Johns Hopkins University
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Pearls and Pitfalls in Cardiovascular Imaging
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Summary
Imaging description
Ductus diverticulum (DD) is an anatomic variant incidentally found at cardiovascular imaging characterized by a smooth bulge of the anterior wall of the aorta at the aortic isthmus, just distal to the origin of the left subclavian artery.
DD is best visualized on sagittal oblique reconstructions on CT, MRI, or digital subtraction angiography (DSA) (Figures 57.1 and 57.2). DD may be difficult to appreciate on standard axial images. On reconstructions, it is recognized as an anteriorly directed bulge of the undersurface of the aortic arch that extends to the proximal descending thoracic aorta. DD has smooth, gentle margins, and obtuse shoulders.
Importance
DD must not be confused with traumatic aortic transection or ductus arteriosus aneurysm, both of which can occur at the same location and have a greater risk of morbidity and mortality.
Typical clinical case scenario
DD is typically encountered as an incidental finding on CT, MR or DSA and is of no clinical significance. It occurs in approximately 26% of adults and requires no follow-up or treatment.
Differential diagnosis
Traumatic aortic transection, also known as post-traumatic pseudoaneurysm, is found in patients with a history of highvelocity trauma. At cross-sectional imaging, aortic transections arise from the anterior wall of the aorta at the isthmus, similar to DD. However, aortic transections have acute angles with the aortic wall, are irregular in shape and size, and often have a visible intimal flap (Figure 57.3). There may be a narrow neck that communicates with the aorta. Associated periaortic and mediastinal hematoma are typically present with traumatic aortic transection.
Aneurysm of the ductus arteriosus is a rare entity characterized by a saccular aneurysm of the undersurface of the aortic arch in the region of the ductus arteriosus (Figure 57.4). Wall calcifications and partial thrombosis are frequently present. Some believe this entity is due to incomplete obliteration of the patent ductus arteriosus during early development that results in a blind-ending stump communicating with the aortic lumen. Progressive enlargement occurs over years.
Case 48 - Pseudothrombus on dark blood images
- from Section 6 - Cardiovascular MRI artifacts
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- By Stefan L. Zimmerman, Johns Hopkins Medical Centre
- Edited by Stefan L. Zimmerman, Elliot K. Fishman
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- Book:
- Pearls and Pitfalls in Cardiovascular Imaging
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- 05 June 2015
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- 21 May 2015, pp 150-153
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Summary
Imaging description
High-signal mimicking thrombus can occur in cardiac chambers on inversion recovery-based dark blood images due to slow flow. Double inversion recovery dark blood images use an initial non-slice-selective 180 degree inversion pulse followed immediately by a second slice-selective inversion pulse in the plane of interest. The net effect is to invert all protons outside of the imaging plane while leaving protons in the plane unaffected. Image acquisition begins when inverted blood protons cross the null point during T1 recovery, typically corresponding to mid-diastole. The sequence relies on flowing blood to replace non-inverted blood protons in the image plane with nulled blood from outside the plane. If there is slow moving blood in a cardiac chamber, there will be incomplete blood suppression. In patients with localized hypokinetic regions, artifactual high signal in these regions of stasis is common and can mimic thrombus (Figure 48.1). This is also common in the subendocardial region in patients with reduced ejection fraction due to slow flow in trabeculations (Figure 48.2).
Importance
Misdiagnosis of thrombus in cardiac chambers could lead to risks from anticoagulation and additional unnecessary followup imaging.
Typical clinical scenario
Artifactual signal from slow flow on dark blood images is common in the left ventricular apex, both in the setting of a global cardiomyopathy or prior apical myocardial infarction. However, artifactual high signal can be seen anywhere there is sluggish flow, including the right ventricle and atria.
Differential diagnosis
Pseudothrombus on dark blood images should be distinguished from a true thrombus. Both of these entities can occur in the setting of blood stasis. However, unlike dark blood artifacts, true thrombus should be present on all pulse sequences both pre- and post-contrast (Figure 48.1).