Published online before print August 14, 2006, 10.1148/radiol.2411051163
(Radiology 2006;241:76-82.)
© RSNA, 2006
Prevalence and Clinical Importance of Aortic Valve Calcification Detected Incidentally on CT Scans: Comparison with Echocardiography1
Ralf Koos, MD,
Harald Peter Kühl, MD,
Georg Mühlenbruch, MD,
Joachim Ernst Wildberger, MD,
Rolf W. Günther, MD and
Andreas Horst Mahnken, MD
1 From the Departments of Cardiology (R.K., H.P.K.) and Diagnostic Radiology (G.M., J.E.W., R.W.G., A.H.M.), University Hospital Aachen, University of Technology Aachen, Pauwelsstrasse 30, 52074 Aachen, Germany. Received July 11, 2005; revision requested September 19; revision received October 10; accepted November 14; final version accepted January 2, 2006.
Address correspondence to R.K. (e-mail: rkoos{at}ukaachen.de).
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ABSTRACT
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Purpose: To evaluate retrospectively the prevalence and grade of aortic valve calcification incidentally detected on chest multi–detector row computed tomographic (CT) scans and to compare the grade of calcification with the severity of aortic valve disease as assessed with echocardiography.
Materials and Methods: Patient informed consent was waived by the institutional board on medical ethics that approved this study. The authors identified 402 patients (231 men and 171 women; mean age, 62.5 years ± 12.1) of 1820 patients who underwent chest multi–detector row CT between July 2001 and August 2004 and also underwent echocardiography. Aortic valve calcification at multi–detector row CT was visually graded on a scale ranging from 0 to 4 (0 = no calcification, 4 = severe calcification). CT findings were correlated with hemodynamic data obtained at echocardiography. Patients without aortic stenosis were compared with patients with aortic stenosis. The Student t test, Spearman correlation coefficient, 
2 analysis, and an unweighted 
test were used to compare results.
Results: Aortic valve calcification was noted on multi–detector row CT scans in 72 of the 402 patients (18%). Twelve of 20 patients (60%) with grade 3 or grade 4 calcification on CT scans had aortic stenosis at echocardiography, compared with only nine of 382 patients (2.4%) with grade 0–2 calcification (P < .001). Significant correlations were observed between the grade of aortic valve calcification and the echocardiographically determined mean (r = 0.45, P = .03) and peak transvalvular gradient (r = 0.47, P = .03). There was substantial agreement between the grade of valve calcification at multi–detector row CT and the severity of aortic valve disease at echocardiography ( = 0.67).
Conclusion: Aortic valve calcification was an incidental finding on 18% of multi–detector row CT scans. The grade of aortic valve calcification is correlated with the hemodynamic severity of aortic valve disease as determined with echocardiography.
© RSNA, 2006
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INTRODUCTION
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Aortic valve calcification is often seen incidentally on chest computed tomographic (CT) scans obtained for a variety of noncardiac indications, but the clinical importance of this finding is uncertain. Moderate or severe aortic valve calcification as assessed with echocardiography has been shown to be a strong and independent predictor of adverse clinical outcomes, including aortic valve replacement, and to be associated with an increased rate of death (1). Previous studies have shown a good correlation between aortic valve calcification demonstrated by multi–detector row CT and the severity of valve stenosis (2–4). Thus, the purpose of our study was to evaluate retrospectively the prevalence and grade of aortic valve calcification detected incidentally on chest multi–detector row CT scans and to compare the grade of calcification with the severity of aortic valve disease as assessed with echocardiography.
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MATERIALS AND METHODS
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Patients
Our institutional board on medical ethics approved our study and waived patient informed consent due to the retrospective nature of the study. We reviewed computer records of all patients who underwent multi–detector row CT of the chest at our institution between July 2001 and August 2004 (n = 1820) and identified 408 patients who had undergone both chest multi–detector row CT and echocardiography. Six patients with aortic valve replacement were excluded from further analysis. The remaining 402 patients (231 men, 171 women; mean age, 62.5 years ± 12.1 [standard deviation]; age range, 32–91 years) were included in our study.
Indications for chest CT included evaluation of thoracic and extrathoracic malignant tumor, pulmonary or pleural infection, pulmonary embolism, postoperative and posttraumatic abnormalities, and assessment of thoracic aortic aneurysm or dissection. No CT scan was obtained specifically to evaluate aortic valve disease. Indications for echocardiography comprised evaluation of left ventricular function and wall motion abnormalities, valvular heart disease, assessment of pericardial effusion, and evaluation of pulmonary hypertension. The mean interval between multi–detector row CT and echocardiography was 56.0 days ± 74.5.
Multi–Detector Row CT
Multi–detector row CT examinations were performed in 187 of 402 patients (47%) with a four–detector row CT scanner (Somatom Volume Zoom; Siemens, Forchheim, Germany) and in 215 of 402 patients (53%) with a 16–detector row CT scanner (Sensation 16; Siemens). All CT examinations were performed without electrocardiographic gating, during inspiratory breath hold.
Intravenous contrast material (Ultravist 370; Schering, Berlin, Germany) was administered to 228 patients (57%); 80 mL of contrast material (flow, 3 mL/sec) was injected for four–detector row CT, and 90 mL (flow, 4 mL/sec) for 16–detector row CT. In all patients, contrast material injection was followed by a 30-mL saline chaser injection. Scanning and reconstruction parameters for contrast material–enhanced and unenhanced examinations are given in Table 1. Scans were reconstructed with an effective section thickness of 5 mm and an increment of 4 mm. The field of view was individually adapted to the patient's body habitus. Image analysis was performed at a separate computer workstation (Leonardo; Siemens).
CT numbers were measured on four consecutive transverse sections from 1-cm2 regions of interest (A.H.M.). The latter were placed in the ascending aorta 2 cm above the origin of the left coronary artery. The mean of the four measurements was determined and used for further analysis.
Image Interpretation
Two experienced radiologists (A.H.M., with more than 6 years of experience in cardiac CT imaging; one nonauthor radiologist with more than 5 years of experience in cardiac CT imaging) who were unaware of the echocardiographic findings independently reviewed all multi–detector row CT scans. Aortic valve calcification was judged to be present when linear or punctate calcification was central to the aortic annulus. The severity of aortic valve calcification was graded by using a five-point scale that was agreed on before the images were evaluated. Grade 0 denoted no calcification; grade 1, minor valvular calcification that was minimally visible in the form of small spots on multi–detector row CT scans; grade 2, mild localized calcification; grade 3, moderate calcification; and grade 4 severe aortic valve calcification involving all three cusps. Disagreements between the two radiologists were resolved by means of a final consensus reading.
Echocardiography
In all patients, a comprehensive echocardiographic study that included M-mode two-dimensional echocardiography and Doppler echocardiographic measurements was performed by two experienced sonographers (12—14 years of experience in echocardiography) with a commercially available ultrasonographic system (Vivid 7; GE Medical Systems, Horton, Norway). Continuous-wave and pulsed-wave Doppler echocardiography was performed to assess transaortic peak and mean pressure gradients. Flow velocity was measured from an apical window. An experienced cardiologist who was unaware of the radiologic findings (R.K., with 5 years of experience in echocardiography) reviewed all echocardiograms.
Aortic valve sclerosis was defined as a focal area of increased echogenicity and thickening of the aortic valve leaflets with a transaortic flow velocity of less than 2.5 m/sec at transthoracic echocardiography, according to the criteria of Otto et al (5). Patients with a transaortic flow velocity of at least 2.5 m/sec were classified as having aortic stenosis. The severity of aortic stenosis was defined according to the mean transvalvular instantaneous gradient: mild aortic stenosis,gradient less than 25 mm Hg; moderate aortic stenosis, gradient of at least 25 mm Hg but less than 50 mm Hg; and severe aortic stenosis, gradient 50 mm Hg or higher (6).
Statistical Analysis
Continuous variables are expressed as mean values ± standard deviations. The Student t test was used to compare continuous variables. Categorical data were presented as frequencies and compared with 2 analysis. The relationship between the grade of aortic valve calcification at CT and the hemodynamic severity of aortic valve stenosis determined with echocardiography was analyzed with the Spearman correlation coefficient. The agreement between the grade of valve calcification at CT and the severity of aortic valve disease assessed with echocardiography was evaluated with an unweighted test. According to the method of Landis and Koch (7), the statistics were valued as follows: 0–0.20, low agreement; 0.21–0.40, moderate agreement; 0.41–0.60, good agreement; 0.61–0.80, substantial agreement; and more than 0.81, perfect agreement (7). Significant differences were defined as those with P values less than .05. Statistical analysis was performed with SPSS 10.0 (SPSS, Chicago, Ill).
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RESULTS
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The mean CT number in the ascending aorta was 267 HU ± 32 on contrast-enhanced scans and 42 HU ± 7 on unenhanced scans.
Prevalence and Severity of Aortic Valve Calcification
Aortic valve calcification was noted on multi–detector row CT scans in 72 of the 402 patients (18%) (Table 2). Forty-two patients (10%) had grade 1 aortic valve calcification, 10 (2%) had grade 2 aortic valve calcification, 19 (5%) had grade 3 aortic valve calcification, and one (0.2%) had grade 4 aortic valve calcification (Figs 1–4). No difference was observed in the prevalence of aortic valve calcifications between unenhanced scans (38 of 174 patients [22%]) and contrast-enhanced scans (34 of 228 patients [15%]; P = .07). The prevalence and severity of aortic valve calcification detected with four–detector row and 16–detector row CT are shown in Table 3.
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Figure 1a: (a) Transverse chest multi–detector row CT scan of a 64-year-old man shows grade 1 aortic valve calcification (arrow). (b) Echocardiogram reveals aortic sclerosis and mild calcification (arrow) of aortic valve leaflets with involvement of the noncoronary and right coronary cusp.
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Figure 1b: (a) Transverse chest multi–detector row CT scan of a 64-year-old man shows grade 1 aortic valve calcification (arrow). (b) Echocardiogram reveals aortic sclerosis and mild calcification (arrow) of aortic valve leaflets with involvement of the noncoronary and right coronary cusp.
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Figure 2a: (a) Transverse chest multi–detector row CT scan of a 68-year-old man with grade 2 aortic valve calcification (arrow). (b) Corresponding echocardiogram shows increased echogenicity (arrow) and thickening of an aortic valve leaflet with mild aortic stenosis.
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Figure 2b: (a) Transverse chest multi–detector row CT scan of a 68-year-old man with grade 2 aortic valve calcification (arrow). (b) Corresponding echocardiogram shows increased echogenicity (arrow) and thickening of an aortic valve leaflet with mild aortic stenosis.
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Figure 3a: (a) Transverse chest multi–detector row CT scan shows grade 3 aortic valve calcification (arrow) in a 67-year-old man. (b) Echocardiogram reveals calcified aortic valve leaflets (arrow) with moderate aortic stenosis.
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Figure 3b: (a) Transverse chest multi–detector row CT scan shows grade 3 aortic valve calcification (arrow) in a 67-year-old man. (b) Echocardiogram reveals calcified aortic valve leaflets (arrow) with moderate aortic stenosis.
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Figure 4a: (a) Transverse chest multi–detector row CT scan shows grade 4 aortic valve calcification (arrows) in a 75-year-old man. (b) Corresponding Doppler echocardiogram shows a peak velocity of 5.51 m/sec, for a peak gradient of 121 mm Hg across the aortic valve, according to the modified Bernoulli equation.
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Figure 4b: (a) Transverse chest multi–detector row CT scan shows grade 4 aortic valve calcification (arrows) in a 75-year-old man. (b) Corresponding Doppler echocardiogram shows a peak velocity of 5.51 m/sec, for a peak gradient of 121 mm Hg across the aortic valve, according to the modified Bernoulli equation.
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There was complete agreement between the observers regarding the presence or absence of aortic valve calcification assessed with multi–detector row CT. In three patients, the observers' grading of aortic valve calcification differed by one grade. The final grading in these patients was achieved by consensus. The prevalence of aortic valve calcification shown by multi–detector row CT was not significantly different between men (44 of 231 patients [19%]) and women (28 of 171 patients [16%]), but this finding was more common in patients at least 65 years old (59 of 198 patients [30%]) than in those younger than 65 years (13 of 204 patients [6%], P < .001).
Echocardiography
At echocardiography, 381 patients had no evidence of aortic stenosis. Of these patients, 308 did not have aortic valve sclerosis, while 73 (18% of all 402 patients) patients had aortic valve sclerosis. Of the 21 patients with aortic valve stenosis, 12 patients (3%) had mild, six (1%) had moderate, and three (0.7%) had severe aortic stenosis (Table 2). Multi–detector row CT revealed aortic valve calcification in 20 of 21 patients (95%) with aortic stenosis.
Aortic Valve Calcification versus Severity of Aortic Valve Stenosis
The relationship between the grade of aortic valve calcification at multi–detector row CT and the severity of aortic valve disease at echocardiography (Table 2) showed substantial agreement between these findings ( = 0.67). Twelve of 20 patients (60%) with grade 3 or 4 calcification at multi–detector row CT had aortic stenosis at echocardiography, whereas only nine of 382 patients (2%) had grade 0–2 calcification (P < .001). In addition, there were significant correlations between the grade of aortic valve calcification and both the echocardiographically determined mean (r = 0.45, P = .034) and peak transvalvular instantaneous gradient (r = 0.47, P = .029) in patients with aortic stenosis.
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DISCUSSION
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Nonrheumatic calcific aortic stenosis is the most common valvular heart disease in the elderly, with a prevalence of 2%—7% in the population older than 65 years (8). The grade of calcification appears to correlate with the rate of disease progression (9). Moreover, moderate or severe aortic valve calcification has been shown to be a strong and independent predictor for adverse clinical outcomes, including an increased rate of death and aortic valve replacement (1). As shown by several studies (2–4), the degree of aortic valve calcification as assessed with cardiac multi–detector row spiral CT is associated with the severity of aortic stenosis. Several authors (10–12) have reported that aortic valve calcification visible on chest radiographs indicates significant aortic stenosis.
Conventional CT is often used for noncardiac indications, but the clinical relevance of aortic valve calcification incidentally detected on CT scans is uncertain. In a retrospective study of 100 CT scans, Woodring and West (13) found five patients with aortic valve calcification. At echocardiography, three of these five patients had aortic valve gradients that ranged from 27 to 36 mm Hg. However, the study was limited by the small number of patients with aortic valve calcification seen at CT. Another possible explanation for the higher prevalence of aortic valve calcification in our study is that we included patients with minor aortic valve calcification, and such patients were not included in the former study. Therefore, it is important to mention that only 5% of our patients had moderate or severe (grade 3 or 4) calcification, a figure comparable to that reported by Woodring and West (13).
In our retrospective study, 18% of patients had aortic valve calcification. Our results are somewhat similar to those in a large study of 1812 patients who underwent electron-beam tomography to assess coronary artery calcification (14). In that study, incidental aortic valve calcification was found in 13% of the patients.
Echocardiography demonstrated aortic stenosis in 21 of the 72 patients with aortic valve calcification shown by multi–detector row CT in our study. Only one patient without aortic valve calcification had moderate aortic stenosis demonstrated at echocardiography. Older patients had a significantly higher prevalence of aortic valve calcification, mainly due to an idiopathic degenerative process (15). This finding is consistent with the findings of earlier studies on aortic valve calcification that used other imaging techniques (10,11,13).
There was no difference concerning the frequency of aortic valve calcifications between unenhanced and contrast-enhanced studies. These results were confirmed by Hunold et al (14), who found no effect of contrast agents on the overall and organ-related frequency of extracoronary findings.
Minor aortic valve calcification is a common finding on multi–detector row CT scans and is usually hemodynamically unimportant. Nevertheless, given the high prevalence of incidental aortic valve calcification and the fact that 40% of patients with grade 3 or 4 calcification have moderate or severe aortic stenosis at echocardiography, it is important to evaluate aortic valve calcification carefully. Because there is a significant correlation between the grade of aortic valve calcification and the echocardiographically determined hemodynamic severity of calcific aortic valve disease, patients with grade 3 or 4 aortic valve calcification at multi–detector row CT may require further functional assessment with echocardiography.
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ADVANCES IN KNOWLEDGE
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- Aortic valve calcification was noted in 18% of multi–detector row CT scans as an incidental finding.
- A significant correlation was observed between the grade of aortic valve calcification and the echocardiographically determined severity of aortic valve disease.
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FOOTNOTES
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Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, all authors; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.K., H.P.K., G.M., A.H.M.; clinical studies, R.K., A.H.M.; statistical analysis, R.K., H.P.K., G.M., J.E.W.; and manuscript editing, R.K., J.E.W., R.W.G., A.H.M.
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- Task Force on Practice Guidelines (Committee on Management of Patients with Valvular Heart Disease). ACC/AHA guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association. J Am Coll Cardiol 1998;32:1486–1588.[Free Full Text]
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ABSTRACT
INTRODUCTION
