Author: Sohail G Contractor, MD, Staff Physician, Department of Radiology, University of Medicine and Dentistry of New Jersey
Coauthor(s): Pierre D Maldjian, MD, Associate Professor, Department of Radiology, University of Medicine and Dentistry, New Jersey Medical School; Consulting Staff, Department of Diagnostic Radiology, University Hospital; Mysore Seetharaman, MD, Consulting Staff, Department of Internal Medicine, Ida G Israel Community Health Center, Coney Island Hospital; Hani H Abu-Judeh, MD, Consulting Staff, Department of Radiology, University of Medicine and Dentistry of New Jersey Hospital; Farid Thanawala, MD, Assistant Professor, Department of Interventional Radiology, University of Massachusetts; Staff Radiologist, Wachussett Radiology, Heywood Hospital
Radiologic detection of calcifications within the heart is quite common. The amount of coronary artery calcification correlates with the severity of coronary artery disease (CAD). Calcification of the aortic or mitral valve may indicate hemodynamically significant valvular stenosis. Myocardial calcification is a sign of prior infarction, while pericardial calcification is strongly associated with constrictive pericarditis. Therefore, detecting and recognizing calcification related to the heart on chest radiography and other imaging modalities such as fluoroscopy, CT, and echocardiography may have important clinical implications.
In patients with diabetes mellitus, by determining the presence of coronary calcifications, patients at risk for future myocardial infarction and coronary artery disease could be identified, and future events could be excluded if no coronary calcifications were present.1
In an asymptomatic population, determination of the presence of coronary calcifications identified patients at risk for future myocardial infarction and coronary artery disease independent of concomitant risk factors. In patients without coronary calcifications, future cardiovascular events could be excluded.2
Calcification of the pericardium usually is preceded by a prior episode of pericarditis or trauma. Infectious etiologies for pericarditis include viral agents (eg, coxsackievirus, influenza A, influenza B), tuberculosis, and histoplasmosis.
Pericardial disease from systemic lupus erythematosus, rheumatic heart disease, uremic pericarditis, and hemopericardium (posttrauma or cardiac surgery) also may result in pericardial calcification. Occasionally, pericardial tumors, such as intrapericardial teratomas and pericardial cysts, can calcify (Images 1-2).
Of patients with pericardial calcification, 50-70% have constrictive pericarditis. Extensive calcification may be present without signs or symptoms of pericardial constriction.
On chest radiographs, pericardial calcification appears as curvilinear calcification usually affecting the right side of the heart (Images 3-4). This is often visualized better on lateral chest radiographs than on frontal views. Calcifications associated with tuberculous pericarditis present as thick, amorphous calcifications along the atrioventricular groove. This pattern may be observed less commonly with other forms of pericarditis as well.
Pericardial calcification is seen more commonly over the right ventricle; in contrast, myocardial calcification is seen more often over the left ventricle (LV) and rarely involves the right atrium or ventricle.
CT is the best technique to detect pericardial calcification; however, overpenetrated films, conventional tomography, fluoroscopy, and MRI may be helpful.
Myocardial calcification is more common in males than in females and usually occurs in patients who have sustained sizable infarcts and have survived more than 6 years after infarction. Most of these patients have a dominant right coronary artery, since this favors longer survival after infarction in the region of the left anterior descending coronary artery.
Approximately 8% of patients who sustain a large myocardial infarction develop myocardial calcification. In these patients, infarcts usually are large and most frequently involve the anterolateral wall of the LV. LV aneurysm usually is present.
Myocardial calcification is identified as thin and curvilinear shaped and usually appears toward the apex of the LV. The associated contour abnormality from the aneurysm is frequently noted. Rarely, calcification can appear spherical or platelike.
The walls of the LV rarely calcify, and calcification of the mural thrombus in the aneurysm is more common. Rarely, calcification is noted in cardiac tumors, such as rhabdomyomas and endotheliomas (Images 5-6).
Left Atrial Calcifications
Detection of left atrial wall calcification has significant clinical implications. Most of these patients have congestive heart failure and atrial fibrillation from long-standing mitral valve disease. Mural thrombi secondary to atrial fibrillation are a frequent source of systemic and pulmonary emboli. Possible complications during cardiac surgery include dislodgement of thrombi, which results in cerebral embolism and uncontrollable hemorrhage if the left atrium (LA) is entered through the calcified region because of LA wall rigidity. LA calcification usually is secondary to endocarditis resulting from rheumatic heart disease, and the amount of calcification is often related to the duration of untreated disease.3
LA calcification may be in the endocardial or subendocardial layer or within a thrombus. Calcification is usually thin and curvilinear (Images 8-9). Three patterns of calcification have been identified.
Type A: Calcification is confined to the LA appendage, the underlying lesion is often mitral stenosis; this type of calcification almost always is associated with thrombus in the appendage.
Type B: The free wall of the LA and mitral valve are calcified, although the valve calcification is not always appreciated from chest radiographs. This pattern indicates advanced mitral stenosis.
Type C: Small area of calcification is confined to the posterior wall of the LA. This results from a jet lesion because of mitral regurgitation and is termed a McCollum patch.
Valvular calcification identified radiographically suggests the presence of a hemodynamically significant stenosis. Dominant valvular insufficiency is not associated with radiographic depiction of calcification, except in patients with calcified stenotic valves secondarily destroyed by endocarditis. The aortic valve calcification is detected most frequently.
Aortic valve calcification
In patients younger than 40 years, a calcified aortic valve usually indicates marked aortic stenosis secondary to a congenital bicuspid aortic valve. In these patients, one cusp of the valve is larger than the other; therefore, the valve cannot function properly, resulting in prolapse, fibrosis, calcification, and stenosis. The average age at which calcification first is detected is 28 years. More than 90% of patients with congenital bicuspid valve have calcification by age 40 years.
In older patients, calcification of the aortic valve may be secondary to aortic sclerosis with degeneration of normal valve leaflets and may be associated with hemodynamically significant aortic stenosis. Aortic valve disease associated with rheumatic heart disease frequently is associated with mitral valve disease. The average age at which aortic valvular calcification first is detected is 47 years in patients with a history of rheumatic fever and carditis. However, aortic valvular calcification is infrequently seen in this entity, and fewer than 10% of patients without congenital bicuspid valve have calcification from age 40-65 years.
* In bicuspid aortic valves, calcification may be nodular, semilunar, or mushroom shaped. A dilated ascending aorta often is seen. A thick, irregular, semilunar ring pattern with a central bar or knob is typical of stenotic bicuspid valves and results from calcification of the valve ring and the dividing ridge of the 2 cusps or the conjoined leaflet (Image 10). Rarely, 3 leaflet valves mimic this pattern because of fusion of 2 of the 3 leaflets. However, none of these features has a high sensitivity or specificity in predicting valvular anatomy
* In patients with aortic sclerosis, calcification usually is nodular. Diffuse aortic dilatation can be observed. Heart size may be normal; however, LV dilation can occur with decompensation. Nodular calcification of the valve also is observed in patients with rheumatic aortic disease. The ascending aorta may be dilated, and signs of rheumatic mitral valve disease may be present.
Mitral valve calcification
Although mitral leaflet calcification is commonly a sequela of rheumatic mitral valve disease, its appearance may be very subtle, not readily apparent on plain films or echocardiograms.4
* A nodular or amorphous pattern of calcification is observed, and signs of rheumatic mitral stenosis frequently are present. These include enlargement of the LA, especially the LA appendage, and pulmonary venous hypertension with cephalization and interstitial edema seen as Kerley B lines.
* Findings that indicate pulmonary arterial hypertension, such as enlarged central pulmonary arteries, can occur in patients with long-standing disease. Detection of mitral valve calcification from chest radiographs is uncommon; echocardiographic detection is far more common. Detection of the calcification has surgical implications, since in such instances valve replacement is preferred to commissurotomy.
Pulmonary valve calcification
Calcification of the pulmonary valve occurs rarely in patients with pulmonary valvular stenosis. If valve calcification is identified radiologically, the gradient across the valve often exceeds 80 mm Hg; valvar calcification also may be observed in patients with long-standing, severe pulmonary hypertension.
Tricuspid valve calcification
Tricuspid valve calcification is rare and most frequently is caused by rheumatic heart disease; however, it has been associated with septal defects, congenital tricuspid valve defects, and infective endocarditis.
Myocardial fibers attach to the annulus or fibrous skeleton of the heart. The cardiac valves are suspended from the annulus.
The mitral annulus commonly calcifies. Annular calcification is a degenerative process seen most often in individuals older than 40 years and is especially common in women. Such calcification is not clinically important unless it is massive, in which case it can cause mitral insufficiency, atrial fibrillation (in presence of dilated LA), conduction defects, and infrequently mitral stenosis.5
A, J, U, or reverse C-shaped bandlike calcification is observed involving the mitral annulus.6 Calcification can appear O-shaped if the anterior leaflet also is involved. Calcification appears bandlike and of uniform radiopacity compared to the nodular and more irregular opacity of mitral valve calcification (Image 11). Sensitivity of detecting mitral annular calcification is substantially higher with echocardiography. Some recent data suggest that this calcification is a form of atherosclerosis and can be used as a marker for ischemic heart disease.
Aortic annular calcification usually is associated with a calcified aortic valve and may extend superiorly into the ascending aorta or inferiorly into the interventricular septum. This type of calcification is often dystrophic, commonly seen in older individuals, and often clinically insignificant.
Tricuspid annular calcification is rare and usually is associated with long-standing and severe pulmonary hypertension.
Calcification involving the aortic arch occurs in more than 25% of normal patients from age 61-70 years. The ascending aorta usually is spared, since the arch and distal aorta most commonly are involved. Patients with hyperlipidemia and diabetes are predisposed to calcific atherosclerosis at a younger age. Calcification in these patients is observed as a curvilinear density along the ascending aorta and the arch.7
Syphilitic aortitis, an inflammatory aortitis involving the ascending aorta, sinuses of Valsalva and the aortic valve, is observed most commonly in patients older than 50 years. Syphilitic aortitis is associated with aortic insufficiency, ascending aortic aneurysms, and a positive serologic test for syphilis. In these patients, angina resulting from occlusion of the ostia of the coronary vessels also can be present. Calcification occurs in a linear pattern along the ascending aorta.
On gross specimen examination, the aorta has been described as revealing a “tree-bark” appearance (Image 12). Focal ascending aortic calcifications also may be observed in patients with Marfan syndrome and focal aortic dissection. Other causes of ascending aortic calcification include false aneurysm and chronic aortic dissection.
Calcification of the pulmonary artery is rare and almost always represents long-standing pulmonary hypertension. It may involve the main and/or central pulmonary arteries (Images 13-14).
Calcification of the ductus arteriosus in adults may be found in patients with ductus patency as well as in those with occluded ductus. In children, calcification of the ligamentum arteriosum indicates a closed ductus. On a frontal chest radiograph, calcification is observed as a curvilinear or nodular density between the aorta and pulmonary trunk.
Coronary (artery) Calcifications
Coronary artery disease (CAD) is the leading cause of death in the United States. According to one American Heart Association estimate, in 1 year, at least 1 million Americans suffer from angina or myocardial infarctions. Of patients who suffer myocardial infarctions, 30% are younger than 65 years and 4% are younger than 45 years.
Evaluation of patients with CAD includes patient history (including review of symptoms and significant coronary risk factors), physical examination, and evaluation of a resting ECG. In patients with symptoms suggestive of CAD, additional investigation, including the physiologic response to stress, may be indicated. This may include stress ECG, stress echocardiography or MRI, or radionuclide perfusion imaging. Coronary calcification is a recognized marker for atherosclerotic CAD. Calcification can be identified on plain radiographs, fluoroscopy, and CT. More reproducible CT evaluation, including quantitation of coronary calcium, may be performed using helical and electron beam CT (EBCT).
Physicians are increasingly using CT detection of calcification to detect subclinical CAD, which may result in early initiation of diet and drug therapy.
Imaging of coronary calcification
Numerous modalities exist for identifying coronary calcification, including plain radiography, fluoroscopy, intravascular ultrasound, MRI, echocardiography, and conventional, helical, and electron-beam CT (EBCT).
Plain radiographs have poor sensitivity for detection of coronary calcification and have a reported accuracy as low as 42% (Image 15).
Fluoroscopy was the most frequently used modality in detecting coronary artery calcification before the advent of CT. The ability of fluoroscopy to detect small, calcified plaques is poor. In a recent study, only 52% of calcific deposits observed on EBCT were identified fluoroscopically. In addition, fluoroscopy is operator dependent, and certain patient characteristics (eg, body habitus, overlying anatomic structures, calcification in overlying anatomic regions) can compromise fluoroscopic examination.8
CT is highly sensitive for detecting calcification. In a study using calcification on CT as a marker of significant angiographic stenosis, sensitivities of 16-78% were reported. Reported specificities were 78-100%, and positive predictive values were 83-100%, suggesting that CAD may be likely to occur when coronary calcification is observed on CT. Conventional CT demonstrates calcification in 50% more vessels than fluoroscopy does in patients with angiographically proven stenosis. However, conventional CT has a slower scan time and is more prone to artifacts from cardiac and respiratory motion and volume averaging than helical or EBCT.9,10
EBCT minimizes motion artifacts, since cardiac-gated imaging can be triggered by the R wave of the cardiac cycle.11 Imaging can be performed in diastole, minimizing cardiac motion. Typically, 20 contiguous, 100-millisecond, 3-mm thick sections are obtained during 1 or 2 breath-holds. Coronary calcification is observed as a bright white area along the course of coronary vessels.
Scans are performed with acquisition times approaching 0.5 second-250 milliseconds; the faster acquisition is possible with the newer multidetector scanners. Calcific deposits are identified as bright white areas along the course of coronary arteries (Image 16).
Coronary calcifications detected on EBCT or helical CT can be quantified, and a total calcification score can be calculated. In this schematic, an arbitrary pixel threshold of +130 Hounsfield units (HU) (+90 for some helical scanners) covering an area greater than 1.0 mm often is used to detect coronary artery lesions. Regions of interest are placed around the area of calcification. Once the region of interest is placed, scanner software displays peak calcification, attenuation in HU, and area of the calcified region in millimeters squared. The volume or Agatson score is displayed. The volume score is the area of the lesion, while the Agatson score is weighted to consider attenuation of pixels, as well as the area.
In the Agatson scoring system, +130-200 HU lesions are multiplied by a factor of 1, +201-300 HU by 2, +301-400 HU lesions by 3, and lesions greater than 401 HU are multiplied by a factor of 4. The sum of the individual lesion scores equals the score for that artery, and the sum of all lesion scores equals the total calcification score.
In one study, a total calcification score of 300 had a sensitivity of 74% and a specificity of 81% in detecting obstructive CAD. The negative predictive value of a zero calcification score was 98%. In another study, sensitivity for detecting calcific deposits in patients with angiographically significant stenosis was 100%, and specificity was 47%. In the same study, 8 patients without calcification showed no angiographic evidence of CAD, while 28 patients with calcification showed mild or moderate CAD.
However, despite the high sensitivity of EBCT, calcification scores do not always predict significant stenosis at the site of calcification. In another study, EBCT was compared with coronary angiography; only 1 patient with stenosis greater than 50% on angiography did not demonstrate coronary calcification on EBCT. Thus, absence of calcification appears to be a good predictor of the absence of significant luminal stenosis. However, absence of calcification does not always indicate the absence of atherosclerotic plaque.
A multicenter study reviewed cardiac event data in 501 mostly symptomatic patients with CAD who underwent both EBCT and coronary angiography. In this group, 1.8% of patients died and 1.2% had nonfatal myocardial infarctions during a mean follow-up period of 31 months. A calcification score of 100 or more was revealed to be highly predictive in separating patients with from those without cardiac events.
The amount of coronary calcification relates to the extent of atherosclerosis, although the relationship between arterial calcification and the probability of plaque rupture is unknown. A zero calcification score is a good predictor of absence of significant CAD. Detecting extensive coronary calcification on CT appears to be a marker of significant atherosclerotic burden and serves as an indication for a more aggressive evaluation of coronary risk factors and an early institution of dietary and/or drug therapy. However, the full implications of coronary calcification detection on CT and the role of this modality must await the results of ongoing investigations.
|Media file 15: Frontal chest radiograph demonstrates calcification involving the left anterior descending coronary artery.|
|Media file 16: Helical non–contrast-enhanced CT reveals calcification involving the left main coronary artery.|