CLINICAL PRACTICE
CASE REPORT |
UNRECOGNIZED CAROTID ARTERY STENOSIS DISCOVERED BY CALCIFICATIONS ON A PANORAMIC RADIOGRAPH
DOV M. ALMOG, D.M.D.,
KARL A. ILLIG, M.D.,
MYO KHIN, D.D.S. and
RICHARD M. GREEN, M.D.
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ABSTRACT
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Background. Approximately 730,000 strokes occur each year in the United States, costing an estimated $40 billion annually. One-half of all strokes are the result of atherosclerotic plaques found in the carotid artery. Such plaques frequently are heavily calcified and can be identified on a panoramic radiograph by the incidental finding of calcifications overlying the carotid bifurcation.
Case Description. The authors found that a 67-year-old asymptomatic woman had calcium deposits overlying both carotid bifurcation regions on a panoramic radiograph. Subsequent duplex ultrasonic examination indicated bilateral, high-grade carotid arterial stenoses. The patient underwent uneventful bilateral carotid endarterectomy.
Clinical Implications. The patient had critical carotid arterial stenoses associated with significant risk of stroke that had not been identified otherwise. The findings on the panoramic radiograph led to appropriate and potentially life-saving treatment. While the positive predictive value of this finding has yet to be defined, the authors believe that calcifications overlying the carotid system region seen on panoramic radiography in an asymptomatic patient should be followed by formal evaluation of the carotid bifurcation.
Carotid artery stenosis, or CAS, is widespread and represents a significant public health problem. Approximately 730,000 strokes occur each year in the United States, costing an estimated $40 billion annually.1,2 One-half of all strokes are believed to be the result of atherosclerotic disease at the carotid bifurcation, which is associated with embolization of atherosclerotic debris or a platelet-fibrin clot formed on the plaque surface (Figure 1
). Carotid endarterectomy, consisting of local removal of the atherosclerotic plaque by a variety of techniques, has been conclusively shown to significantly reduce the risk of stroke in both symptomatic and asymptomatic patients with significant plaque lesions.3,4 Although the specifics of carotid endarterectomy are beyond the scope of this article, the procedure leads to significantly reduced risk of stroke in asymptomatic patients with stenosis of 60 percent or greater, compared with nonoperative therapy consisting of risk-factor modification, antiplatelet agents and observation. Interestingly, these same reports demonstrate that even diagnostic cerebral angiography carries with it an unacceptably high risk of patients’ experiencing stroke (1.2 percent), and for this reason it no longer is used as a screening test.
Unfortunately, the first clinical manifestation of CAS often is a completed stroke that occurs when treatment is too late. Therefore, the issue of screening has been examined extensively, with disappointing results to date. Although duplex ultrasonography—the most accurate screening method short of angiography—is noninvasive and relatively inexpensive, screening all patients is impractical and not cost-effective. In a recent mathematical analysis exploring this issue, Yin and Carpenter5 found that ultrasonic screening of carotid arteries was cost-effective provided that the prevalence of significant disease in the screened population was at least 4.5 percent. The prevalence of severe disease, however, in people older than 65 years of age has been estimated to be less than 1 percent,6 and, therefore, this is not a reasonable strategy. Obviously, identifying at-risk subgroups of patients in whom the prevalence of disease is high would allow for more cost-effective screening.
High-risk groups for whom ultrasonic screening might be cost-effective include those with bruits or atherosclerosis in other parts of the body. Audible cervical bruits are caused by turbulent blood flow and can be caused by tortuousity, high flow rates through otherwise normal vessels, a cardiac problem or CAS. Although the presence of a bruit does not necessarily indicate CAS, most physicians believe that its presence increases the patient’s risk of developing CAS and that it is an indication for ultrasonic evaluation.7–9 In addition, because atherosclerosis tends to be a systemic problem, the incidence of significant CAS in patients with lower-extremity and coronary atherosclerosis is as high as 10 to 12 percent,10,11 and occlusive disease in either location has become a de facto indication for carotid ultrasonography. To date, however, there are no universally accepted screening criteria, and referral for ultrasonic evaluation remains up to the individual physician.
In recent years, a number of publications have described the detection of calcifications in the region of the carotid bulb on panoramic radiographs.12–15 These studies suggest an overall prevalence rate of carotid artery calcifications on panoramic radiographs of approximately 2 to 5 percent in the general dental outpatient population and approximately 5 percent in patients 55 years of age and older. No data yet exist, however, on the relationship between these calcifications, significant CAS and actual stroke risk.
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CASE REPORT
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A 67-year-old white woman came to the University of Rochester Eastman Dental Center New York, for comprehensive dental care. Her medical history revealed noninsulin–dependent diabetes mellitus, hyperlipidemia controlled with oral medication and tobacco use; she had quit using tobacco two years before. She had no history of stroke, transient ischemic attack, amaurosis fugax or other neurological problems, and her primary care physician had not heard any bruits on examination.
A panoramic radiograph taken during her dental examination revealed the presence of multiple, irregular, nonhomogenous radiopacities lying over both the right and the left carotid bifurcations. The calcifications were located inferior to the angle of the mandible and the tip of the hyoid bone and superior to the tip of the thyroid cartilage and the C3, C4 and C5 vertebrae (Figure 2).
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Figure 2. Coned-down view of the preoperative panoramic radiograph. Calcifications (arrows) appear as heterogeneous radiopacities overlying the carotid bifurcations near the tip of the greater horn of the hyoid bone, surrounding and superior to the tip of the thyroid cartilage at the level of the C3, C4 and C5 intervertebral spaces.
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Differential diagnoses included thyroid cartilage tip calcification, triticeous cartilage calcification, aberrant soft-tissue calcifications, calcified lymph nodes, phleboliths, calcified acne and calcification associated with atherosclerosis within the carotid arteries.
After we discussed the diagnoses with the patient’s primary care physician, we referred her to the vascular surgical service at the University of Rochester Medical Center. A vascular surgeon (R.M.G.) took the patient’s medical history and performed a physical examination; these procedures confirmed an absence of symptomatology and bilateral cervical bruits. The vascular surgeon performed carotid duplex ultrasonography, using the ATL-3000 duplex ultrasonic imager (Advanced Technology Laboratories) with a 5-megahertz probe; it revealed bilateral carotid stenosis, with stenosis on the left side being greater than that on the right side. Peak systolic velocities, or PSV, reached 487/184 centimeters per second (PSV/end diastolic velocity, or EDV) on the left side and 325/120 cm/s on the right side corresponding to 80 to 99 percent stenoses (Figure 3); normal values are approximately 100/30 cm/s or less. The diagnosis of carotid stenosis by ultrasonography is made by documenting the increase in the velocity of the red blood cells passing through the narrow opening, rather than direct measurement of diameter itself.
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Figure 3. Color-flow duplex image of the internal carotid artery. The bright, echolucent calcifications anteriorly (yellow arrow) with dark acoustic shadowing below hides the stenosis itself. Calcium blocks the sound waves used in duplex imaging. Note the bright specks (white arrow) indicating the high-velocity, turbulent jet just to the left of the lesion (flow is from right to left).
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After giving informed consent, the patient underwent elective, consecutive endarterectomies performed three months apart, with the left side being completed first. The surgery was performed under general anesthesia with electroencephalographic monitoring. The vascular surgeons obtained exposure by making a conventional incision along the sternocleidomastoid muscle near the angle of the mandible and removed plaque, using eversion endarterectomy with intraoperative, postrepair duplex examination. The plaques on both sides were heavily calcified. Postoperative recovery was uneventful, and the patient resumed her normal activities within one week of each procedure. Follow-up duplex ultrasonography revealed widely patent arteries with no visible stenosis and normal PSV. A coned-down postoperative panoramic radiograph revealed that the surgical clips used for hemostasis in the area of the carotid bifurcation during the endarterectomy were in the same location as the previous calcifications, which then were absent (Figure 4).
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Figure 4. Coned-down view of the postoperative panoramic radiograph showing the surgical clips used for hemostasis at the carotid bulb during the carotid endarterectomy. This radiograph shows the absence of the calcium previously seen in the region of the carotid bifurcation and confirms the presence of the carotid bulb location within the panoramic view.
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DISCUSSION
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Incidental calcifications lying over the carotid bifurcation region sometimes can be seen on oral panoramic radiographs. The patient described in our case report had no signs or symptoms of carotid artery disease and would not have been evaluated or screened for atherosclerotic disease without our finding calcified carotid plaques on a panoramic radiograph. She had bilateral high-grade stenoses with associated high stroke risk3 and received appropriate therapy for her condition based on this incidental observation.
No method of detection for any disease is 100 percent accurate. The utility of this type of observation obviously will depend on the prevalence and amount of calcium within these lesions, which varies from patient to patient. Since calcium is such a common component of atherosclerotic plaques, the presence of calcium in an unusual location, especially lying over the course of a blood vessel commonly affected by this disease, is presumptive evidence of some degree of atherosclerosis. In fact, calcium-lined arteries commonly are seen on plain radiographs of both the lower extremities and abdomen, suggesting occlusive disease in the appropriate context and commonly triggering further evaluation.
Whether or not this atherosclerotic disease is clinically significant will depend on the clinical scenario and, in the case of the carotid bifurcation, the percent stenosis. Percent stenosis is determined best by duplex ultrasonography, which is inexpensive, easily available, accurate and noninvasive.16–18
Angiography, formerly the gold standard of diagnostic studies used to determine CAS, is associated with surprisingly high stroke risk—1.2 percent in the Asymptomatic Carotid Artery Stenosis trial.3 Taking an operative approach to this lesion is standard, and essentially all clinically relevant decisions can be made at the time of exploration. For these reasons, coupled with the expense, discomfort and local morbidity of the procedure, angiography most commonly is reserved for patients with specific indications such as those with suspected subclavian, low-common carotid or intracranial lesions; those whose symptoms do fit their lesions; or those in whom the accuracy of the ultrasonic examination is in doubt. While some investigators have found magnetic resonance angiography to be as accurate as ultrasonography, it is expensive and not portable, and scheduling it involves long wait times.19 Duplex ultrasonography remains the unequivocal diagnostic test of choice, and at our institution it is the sole preoperative imaging modality used in approximately 90 percent of carotid procedures.
Duplex ultrasonography indirectly yields information regarding percent stenosis, by measuring the increase in blood velocity produced by a focal stenosis (the Bernoulli effect). Because most data regarding indications for performing surgery were derived from studies using angiography as the gold standard, and because overall risk and patient status are critically important in making decisions regarding surgery, the decision about when to intervene surgically is surprisingly indistinct. We believe that in asymptomatic patients without major medical illnesses, the risk-benefit ratio favors operating when PSV and EDV approach 300 and 100 cm/s, respectively, or when the PSV ratio between the internal and common carotid arteries exceeds 4.0.16–18 This judgment, however, is complex and must be made on individual bases. We stress that reports simply indicating percent stenosis based on ultrasonography are inadequate for making this decision; raw velocities must be available and interpreted by the vascular surgeons performing the operation in the context of its overall outcome and the circumstances surrounding the patient.
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CONCLUSIONS
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Strokes caused by embolization from atherosclerotic disease at the carotid bifurcation are common and usually occur without warning. Because many significant carotid plaques contain calcium and modern ultrasonic screening is noninvasive, accurate and inexpensive, we suggest that calcifications seen lying over the carotid bifurcation on panoramic radiographs should prompt further evaluation for CAS. However, the numerical relationship between such calcifications and percent stenosis and stroke risk are unknown, and it awaits further investigation.
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FOOTNOTES
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Dr. Illig is an assistant professor, Division of Vascular Surgery, University of Rochester, N.Y.
Dr. Khin is a general practice resident, Eastman Department of Dentistry, University of Rochester, N.Y.
Dr. Green is a professor, Division of Vascular Surgery, University of Rochester, N.Y.
Dr. Almog is an associate professor, Division of Prosthodontics, Eastman Department of Dentistry, University of Rochester, 625 Elmwood Ave., Rochester, N.Y. 14620, e-mail "dov_almog@urmc. rochester.edu". Address reprint requests to Dr. Almog.
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