DOI:10.2214/AJR.06.1002
AJR 2007; 188:1264-1269
© American Roentgen Ray Society
MDCT Detection of Mitral Valve Calcification: Prevalence and Clinical Relevance Compared with Echocardiography
Andreas H. Mahnken1,2,
Georg Mühlenbruch1,
Marco Das1,
Joachim E. Wildberger1,
Harald P. Kühl3,
Rolf W. Günther1,
Malte Kelm3 and
Ralf Koos3
1 Department of Diagnostic Radiology, University Hospital, RWTH-Aachen
University, Pauwelsstrasse 30, D-52074 Aachen, Germany.
2 Applied Medical Engineering, Helmholtz Institute, RWTH-Aachen University,
Aachen, Germany.
3 Department of Internal Medicine I, University Hospital, RWTH-Aachen
University, Aachen, Germany.
Received July 31, 2006;
accepted after revision November 8, 2006.
Address correspondence to A. H. Mahnken
(mahnken{at}rad.rwth-aachen.de).
Abstract
OBJECTIVE. The purpose of this study was to analyze the prevalence
and clinical significance of mitral valve calcification incidentally detected
on chest CT scans in comparison with echocardiography.
MATERIALS AND METHODS. The data of 390 patients (227 men and 163
women; mean age, 62.4 ± 12.2 years) who underwent MDCT of the chest and
echocardiography were retrospectively evaluated. On MDCT, mitral valve leaflet
and annulus calcification were visually graded on a scale of 0-3, with grade 0
denoting no calcification and grade 3 indicating severe calcification. CT
findings were correlated with hemodynamic data obtained at echocardiography.
Unpaired Student's t tests, chi-square analysis, and a weighted-kappa
test were used to compare results.
RESULTS. In 32 (8.2%) of 390 patients, chest MDCT revealed mitral
valve leaflet calcification. Fifteen of these patients (15/390, 3.8%)
presented with mitral valve stenosis. Excellent agreement (
= 0.882)
was seen between the presence of mitral valve calcification on MDCT and
echocardiographically proven mitral valve sclerosis. Mitral valve leaflet
calcification on MDCT and the severity of mitral valve disease on
echocardiography showed a substantial agreement ( = 0.730). A
significant relationship was seen between the degree of mitral valve
calcification on MDCT and the echocardiographically determined severity of
mitral valve disease (no sclerosis vs mitral sclerosis vs mitral stenosis;
p < 0.0001).
CONCLUSION. Mitral valve leaflet calcification on MDCT indicates
mitral valve sclerosis or stenosis. Thus, patients presenting with
incidentally detected mitral valve leaflet calcification on chest CT may
benefit from a functional assessment with echocardiography.
Keywords: calcification • CT • heart • MDCT • mitral valve
Introduction
Mitral valve calcification is regularly seen on chest CT scans that
are obtained for a variety of noncardiac diagnoses. The clinical impact of
this finding, however, is unclear. Only limited data exist that indicate the
presence of mitral valve calcification on CT to be related to mitral valve
disease
[1-3].
Data on the prevalence and clinical relevance of this finding are missing. For
aortic valve calcification, more data are available, proving valvular
calcifications to be related to aortic valve stenosis
[4-7].
Previously, several authors have shown that mitral valve calcification on
chest radiography is related to valvular stenosis
[8,
9]. This finding is found in
patients with a history of rheumatic fever, noninflammatory calcific disease,
and chronic renal failure
[10]. In addition, mitral
valve calcification is related to several other cardiovascular
diseases—an increased risk of stroke
[11], cardiac conduction
defects [12], and
atherosclerosis, including coronary artery calcifications
[13,
14]. Mitral valve
calcification also affects therapy because these patients have a poorer
outcome after balloon valvotomy
[15]. In more than 90% of
patients, mitral valve stenosis is thought to be a sequela of rheumatic
disease [16], with a delay of
up to three decades between the initial manifestations of rheumatic fever and
the development of mitral stenosis
[17]. Therefore, the clinical
relevance of mitral valve calcification as a possible sign of disease is of
interest.
The purpose of this study was to analyze the prevalence and clinical
significance of mitral valve calcification incidentally detected on routine
chest CT in comparison with echocardiography.
Materials and Methods
Patients
All patients (n = 1,788) who underwent MDCT of the chest between
August 2001 and August 2004 were derived from a computer-based retrieval
system of a radiology information system database. The review of the computer
records of these patients identified 393 patients who had undergone chest CT
and echocardiography within a 3-month period. Three patients with a history of
mitral valve replacement were excluded from further analysis. In the remaining
390 patients (227 men, 163 women; mean age, 62.4 ± 12.2 years; range,
33-91 years), the presence of mitral valve leaflet (MVL) and mitral valve
annulus (MVA) calcification on MDCT was correlated with echocardiographic
findings. On average, the interval between MDCT and echocardiography was 48.2
± 37.6 days (range, 1-79 days). Approval and informed consent for
review of patient records and images is not required by our institutional
review board.
Indications for chest CT included evaluation of thoracic and extrathoracic
malignant tumor (n = 993), pulmonary embolism (n = 485), and
infection (n = 163); and assessment of thoracic aortic aneurysm or
dissection (n = 93) and posttraumatic (n = 37) or
postoperative (n = 17) abnormalities.
CT
In 177 (45.4%) of 390 patients, MDCT examinations were performed using a
4-MDCT scanner (Somatom VolumeZoom, Siemens Medical Solutions), and in 213
(54.6%) of 390 patients, using a 16-MDCT scanner (Somatom Sensation 16,
Siemens). All MDCT was performed in end-inspiratory breath-hold without ECG
synchronization. Standardized scanning and reconstruction parameters were
applied to all scans, with the field of view being individually adapted to
each patient's physique (Table
1). In 333 (85.4%) of 390 patients, contrast-enhanced MDCT scans
were available for analysis. For 4-MDCT, 80 mL of contrast material (Ultravist
370 [iopromide], Schering) was administered at a flow rate of 3 mL/s; for
16-MDCT, 90 mL of contrast material (Ultravist 370) was injected at a flow
rate of 4 mL/s. In all patients, contrast material injection was followed by a
30-mL saline chaser bolus injected at the same flow rate as the contrast
material.
All MDCT scans were reviewed as axial images on an external workstation
(Leonardo, Siemens) by a radiologist with 7 years' experience in chest CT. The
reviewer was blinded to the echocardiographic findings. The presence of MVL
and MVA calcification was documented (0 = no MVA calcification, 1 = MVA
calcification). In addition, mitral valve calcifications were quantified using
a 4-point scale that was determined before image analysis, as follows: 0 = no
calcification; 1 = minor valvular calcification that was visible as spotty
calcifications on CT scans; 2 = marked, but circumscribed calcifications; and
3 = diffuse severe valvular calcification involving the anterior and the
posterior leaflets.
Echocardiography
A comprehensive echocardiographic study, including M-mode, 2D
echocardiography, and Doppler echocardiographic measurements, was performed in
all patients by experienced sonographers using a commercially available
sonographic system. The mean transmitral gradient was measured from the
continuous wave Doppler signal across the mitral valve using the modified
Bernoulli equation [18,
19], and planimetry of the
orifice area was performed from the short-axis view
[20]. A cardiologist with 6
years' experience in transthoracic echocardiography, unaware of the MDCT
findings, reviewed all echocardiographic examinations. Mitral valve sclerosis
was defined as a structural abnormality of the mitral valve apparatus with
leaflet thickening and calcification but no diastolic transmitral gradient.
The presence of mitral valve stenosis included additional restriction of
leaflet motion leading to a diastolic transmitral gradient. The severity of
mitral valve stenosis was classified according to the American College of
Cardiology/American Heart Association guidelines
[21]. A valve area > 1.5
cm2 and a mean transmitral gradient < 5 mm Hg was classified as
mild mitral valve stenosis; a valve area between 
1.0 cm2 and
1.5 cm2 and a mean transmitral gradient of 5-15 mm Hg, as
moderate stenosis; and a valve area < 1.0 cm2 and a mean
transmitral gradient > 15 mm Hg, as severe mitral valve stenosis. For
statistical analysis, patients with moderate and severe mitral stenosis were
summarized.
Statistical Analysis
Continuous variables are expressed as mean values plus or minus SDs.
Categoric data are presented as frequencies. Continuous variables were
compared using unpaired Student's t tests, and categoric data were
assessed using chi-square analysis. Weighted-kappa tests were used to analyze
the agreement between the presence and grade of MVL and MVA calcification on
MDCT and the presence and severity of mitral valve disease assessed on
echocardiography. Kappa statistics were interpreted according to Landis and
Koch [22]: 0-0.2, low
agreement; 0.21-0.4, moderate; 0.41-0.6, good; 0.61-0.8, substantial; and >
0.81, perfect agreement. A significance level of 5% was assumed. For
statistical analysis, Medcalc 7.1 (Medcalc Software) was used.
Results
On MDCT, MVL calcification was noted in 32 (8.2%) of 390 patients
(Table 2). None of the patients
showed severe and diffuse calcifications (grade 3). Calcification of the MVA
was present in 36 (9.2%) of 390 patients. Echocardiography revealed mitral
valve sclerosis in 33 (8.5%) of 390 patients; 15 of these patients presented
with mitral valve stenosis (15/390, 3.8%)
(Table 3). All patients with
mitral valve stenosis presented with at least minor MVL calcification. In an
additional three (0.8%) patients without echocardiographic signs of mitral
valve stenosis, MDCT revealed minor calcifications of the MVL. There was an
overlap in the populations with MVL and MVA calcifications. Although some
patients showed only MVL (n = 13) or MVA (n = 17)
calcification, 19 patients presented with both MVA and MVL calcifications
(Fig. 1A,
1B,
1C).
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TABLE 2: Comparison of Presence of Mitral Valve Leaflet (MVL) Calcification on
MDCT and Degree of Valvular Disease on Echocardiography
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TABLE 3: Comparison of Mitral Valve Annulus (MVA) Calcification Detected on MDCT
and Degree of Mitral Valve Disease on Echocardiography
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Fig. 1C —Classification of mitral valve annulus and mitral valve leaflet. In
patients presenting with both mitral valve leaflet (arrows) and
annulus (arrowhead) calcification separation of anatomic structures
was feasible from their position on axial CT images because mitral valve
apparatus is positioned horizontally to scanning plane.
|
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With respect to the frequency of mitral valve calcifications, no difference
was detected between contrast-enhanced (27/333 patients, 8.1%) and unenhanced
(5/57 patients, 8.8%; p = 0.8678) MDCT scans. No significant
difference was seen in the detection of MVL calcification between male
(18/227, 7.9%) and female (14/163, 8.6%) patients, but patients with MVL
calcification detected on CT were older (69.4 ± 8.2 years) than those
without MVL calcification (61.7 ± 12.2 years) (p = 0.003). The
same finding was observed for the presence of MVA calcification, with the
patients without MVA calcification being significantly younger (61.5 ±
12.2 years) than the patients with calcification seen on MDCT (70.6 ±
8.3) (p < 0.0001).
Perfect agreement ( = 0.882) was seen between the presence of MVL
calcification on MDCT and mitral valve sclerosis. The agreement between the
grade of MVL calcification on MDCT and the severity of mitral valve disease on
echocardiography ( = 0.730) was substantial
(Table 2 and Figs.
2A,
2B,
3A,
3B,
4A,
4B and
5A,
5B). A significant
relationship was seen between the degree of MVL calcification on MDCT and the
echocardiographically determined severity of mitral valve disease (no
sclerosis vs mitral sclerosis vs mitral stenosis; p < 0.0001).
Three of 357 patients without mitral valve disease presented with grade 1 MVL
calcification on MDCT, whereas all patients with grade 2 MVL calcification on
MDCT revealed mitral valve stenosis on echocardiography.
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Fig. 4A —75-year-old man with moderate calcification. MDCT scan shows mainly
mitral valve annulus but also mitral valve leaflet calcification (grade 2),
indicating mitral valve stenosis. Pleural effusion is also present.
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Fig. 5A —80-year-old woman with severe calcification. MDCT scan shows severe
but circumscribed mitral valve calcification (grade 2) affecting anterior and
posterior mitral valve leaflets (arrows).
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Fig. 5B —80-year-old woman with severe calcification. Corresponding
echocardiogram depicts thickening and calcification of mitral valve leaflets
(arrows) that are indicative of severe mitral valve stenosis.
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In addition, good agreement was seen between the presence of MVA
calcification and the presence of mitral valve stenosis as detected on
echocardiography ( = 0.498) (Table
3).
Discussion
Mitral valve calcification may be seen in rheumatic mitral stenosis or as a
result of degenerative changes in elderly patients. The latter are often
associated with MVA calcification. Especially extensive degenerative
calcification of the MVA may extend to the valve leaflets, resulting in a
variety of valvular diseases, including mitral valve stenosis. Historically,
radiography and fluoroscopy were used for assessing mitral valve
calcification. Today, routine evaluation of patients with mitral valve disease
is performed using echocardiography. This approach permits an accurate
determination of functional data of the mitral valve, including identification
of flail mitral valves, measurement of transvalvular pressure gradients, and
assessment of morphologic valve abnormalities such as thickening or
calcification of the MVL and MVA
[23]. So far, only limited
data are available on the role of CT in assessing mitral valve calcification
[1-3].
Woodring and West [1] found
mitral valve calcifications in five patients 70 years old or older in a group
of 100 patients examined with sequential single-detector CT. Although four of
these patients presented with signs of valvular heart disease, none of them
had evidence of mitral valve stenosis. However, the study was hampered by
several factors: First, it was performed at low temporal and spatial
resolutions, with a gantry rotation time of 2 seconds and a slice thickness of
10 mm. Consequently, the authors failed to distinguish calcification of the
MVL from MVA calcification. Second, only a small number of patients with
mitral valve calcification were included in that study.
In a study of accidental findings on electron beam CT, Hunold et al.
[24] reported mitral valve
calcification in 131 (7.2%) of 1,812 patients; the frequency of these findings
is similar to the results of our study. However, echocardiography was
available in only 30 patients, revealing only mild mitral regurgitation or
mitral stenosis. The severity of calcification was not assessed in that study
[24]. The most recent study
dealing with mitral valve calcification by Willmann et al.
[2] proved the differentiation
between MVL and MVA calcification is feasible with retrospectively ECG-gated
MDCT. MVL calcifications were detected in 15% of their patients and MVA
calcifications, in 45%. Because of the small study population, with only 20
patients having known mitral valve disease, no conclusions as to the clinical
impact of incidentally found mitral valve calcification could be drawn.
In our study, we were able to differentiate MVL from MVA calcification. The
presence of MVL calcification indicated the presence of mitral sclerosis or
stenosis. This finding contrasts with the results reported by Woodring and
West [1], but this difference
might be explained by their inability to differentiate MVL calcification from
MVA calcification. Correspondingly, the correlation between the presence of
mitral valve sclerosis or stenosis was worse for MVA calcification. Although
our data suggest a good agreement between MVA calcification and mitral valve
stenosis, the discriminative power of MVA calcification on MDCT is
insufficient for clinical purposes (Table
3). Instead, our results indicate the need to differentiate
between MVL calcification and MVA calcification. Knowledge of the latter might
be important because MVA calcification is known to be associated with a higher
incidence of hypertrophic cardiomyopathy, atrial fibrillation, and stroke
[25,
26]. Moreover, a relationship
with the presence of coronary artery calcifications and atherosclerotic
disease has been shown [14,
27].
A limitation of our study is the missing differentiation of rheumatic from
degenerative mitral valve disease. However, this differentiation is
dispensable for our purposes because this information will not change further
diagnostic workup in the presence of mitral valve calcification incidentally
detected on CT. Another limitation is the inclusion of data from
contrast-enhanced and from unenhanced studies. However, the frequency of
mitral valve abnormalities was similar in both groups. In addition, motion
artifacts may negatively influence depiction of the mitral valve because
routine chest CT is performed without ECG gating. Nevertheless, with subsecond
gantry rotation time, image quality was sufficient to differentiate MVL
calcification from MVA calcification in all patients.
Quantification of the MVL and MVA calcification was omitted because motion
artifacts and the presence of contrast material are known to limit the
reliability of such measurements
[28,
29]. Because ECG-gated MDCT
eliminates motion artifacts, quantification of mitral valve calcifications may
become a future application for cardiac MDCT. The latter potentially improves
the discriminative power of MDCT for assessing the severity of mitral valve
stenosis, similar to the quantitative assessment of aortic valve
calcifications [5,
6]. To date, however, ECG-gated
MDCT is of no relevance in the routine workup of mitral valve
abnormalities.
In conclusion, our data suggest that MVL calcification is a pertinent
indicator for mitral valve sclerosis or stenosis, whereas MVA calcification is
not suited to reliably determine the presence of mitral valve disease.
Although the quantity of calcification is related to the severity of disease,
no unequivocal assessment of the hemodynamic significance can be made.
Therefore, patients presenting with incidentally detected MVL calcification on
chest CT may benefit from echocardiography and further diagnostic workup.
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Abstract
Introduction
