Detection of Carotid Atheromas by Panoramic Radiography
Arthur H. Friedlander, DMD; and Allan G. Farman, BDS, PhD, MBA, DSc
OBJECTIVE: To develop a rational differential diagnosis of a radiopacity in the region of the carotid artery bifurcation detected in a panoramic radiograph based upon knowledge of which patients are at greatest risk for stenotic atherosclerotic lesions. STUDY DESIGN: In 2007, the American Society of Neuroimaging (ASN) published guidelines for physicians that identified groups of patients who should be screened with Doppler ultrasound for carotid artery atheromas. These recommendations were the result of an evidence-based review of published studies that identified "at risk" subsets of patient populations based upon the expected prevalence of the lesions and the anticipated benefit from therapeutic interventions. The ASN study and recommendations were examined to ascertain components adjunctive to the interpretation by dentists of radiopacities detected in the carotid bifurcation regions during the assessment of panoramic dental radiographs. RESULTS: Individuals who are older than 60, hypertensive, diabetic, currently smoke, or who have vascular disease of the coronary arteries, renal arteries, or the abdominal aorta are at the highest risk of having an atheroma. CONCLUSION: Familiarity with the guidelines for screening of extracranial carotid artery disease developed by the ASN can assist dentists in identifying the subgroups of patients likely to demonstrate a calcified carotid artery atheroma on a panoramic radiograph.
Each year more than 700,000 Americans suffer a stroke and 275,000 of these individuals die.1 The most frequent cause of these strokes is an embolism that has broken off from an atheroma at the bifurcation of the common carotid artery or from the proximal portion of the internal carotid artery and has traveled to and occluded a branch of the middle cerebral artery.2,3 Since 1981, numerous research studies have demonstrated that calcified atherosclerotic lesions located in the bifurcation region can be seen on panoramic radiographs in the area 1.5 cm to 2.5 cm inferior-posterior to the angle of the mandible.4-8 These lesions appear as nodular radiopaque masses or radiopaque vertical lines at approximately the level of the interspace between the third and fourth cervical vertebrae.9 The prevalence rate of detecting such lesions on film-based panoramic radiographs in the general dental population ranges between 3% and 5%.10-12
Confirmation as to the hemodynamic significance (that is, flow-limiting lesions with stroke-causing potential) identified by panoramic radiography is provided by a 2005 study that described 65 neurologically asymptomatic individuals with calcified carotid artery atheromas (38 with bilateral opacities and 27 with unilateral opacities) who were referred for Doppler ultrasound spectral analysis.13 Of the 103 sides of the neck with radiographically identified atheromas, ultrasound demonstrated that none of these internal carotid arteries were normal: 81 (79%) had less than 50% stenosis, 18 (17%) had 50% to 69% stenosis, and four (4%) had 70% or greater stenosis. The ability of panoramic radiography to identify clinically significant (> 60% occlusion) occult stenotic lesions in neurologically asymptomatic individuals has great public health importance given that the American Heart Association Guidelines recommend elective surgical removal (endarterectomy) of these lesions to prevent strokes and save lives.14,15
Recent research findings have noted that heterogeneous plaques consisting of lipids, fibrous material, and calcium are more likely to cause neurologic symptoms (ie, cerebrovascular accident, transient ischemic attack) than are homogeneous, solidly calcified ones. Panoramic radiography, unlike multidetector-row computed tomography angiography, is not capable of distinguishing plaque morphology or calcium content, but a recently published outcome study did demonstrate that atheromas imaged by these radiographs do likely embolise, causing neurologic symptoms. The study also demonstrated that these lesions are also markers of the overall atherosclerotic load given that their presence often heralded future myocardial infarctions and the need for hospitalization to treat angina and perform revascularization procedures.16,17
Atheroma prevalence rates are even higher in groups of individuals harboring multiple atherogenic risk factors. For example, Beckstrom et al recently demonstrated that 24% of digital panoramic radiographs obtained from untreated head-and-neck cancer patients show calcified carotid artery atheromas.18 This is not surprising given the patients’ atherogenic risk factor burden of tobacco and alcohol abuse and inflammation arising from severe periodontitis, which caused extensive alveolar bone loss. Similarly, atheromas prevalence rates range from 20% to 35% for those with type 2 diabetes mellitus, metabolic syndrome and obstructive sleep apnea, and systemic illness associated with accelerated forms of generalized atherosclerosis.19-21 Calcified carotid plaques are readily discerned using digital panoramic technologies.
In 1999, US dentists in private practice performed more than 17 million panoramic imaging studies and in 2006 the American Dental Association’s Council on Scientific Affairs recommended that panoramic radiographs made for dental purposes should also be evaluated for the presence of carotid artery calcifications.22,23 In 2007, the American Society of Neuroimaging (ASN) published guidelines for physicians that identified groups of patients who should be screened with Doppler ultrasound for carotid artery atheromas. These recommendations were the result of an evidence-based review of published studies that identified "at risk" subsets of patient populations based upon the expected prevalence of the lesions and the anticipated benefit from therapeutic interventions such as anticoagulant therapy, endarterectomy, or stent placement.24
Familiarity with the demographic and clinical characteristics of these "at risk" groups based on atheroma prevalence rates (rather than efficacy of treatment) is particularly helpful to dentists when developing a rational differential diagnosis of an atheroma-like calcification on the radiograph of a neurologically asymptomatic patient. The information contained in the guidelines is vital because of the numerous other confounding radiopacities that may be visualized in the region (hyoid bone, epiglottis, stylohyoid ligament, gland sialoliths, calcified triticeous or thyroid cartilages, calcified lymph nodes, and noncarotid phleboliths).
A recent study has demonstrated that the prevalence of significant carotid artery stenosis (defined as greater than 50% stenosis by Doppler ultrasound study) among neurologically asymptomatic individuals in the general population without accepted cardiovascular risk factors (ie, history of coronary artery disease, previously diagnosed hypertension, and current cigarette smoking) is 2%. However, when subgroups of the general population have some of these risk factors, then their risk rises substantially. Specifically, persons older than 60 harboring one factor are at 6% risk of significant stenosis; with two risk factors, they are at 14% risk; with three factors, they are at 16% risk; and with four risk factors, they are at 67% risk.25 In a somewhat similar study which defined significant stenosis as greater than 60% stenosis, risk groups were stratified based on total scores obtained for age older than 65 (4 points), coronary artery disease (2 points), current smoking (1 point), and hyper-cholesterolemia (1 point).26 Approximately one third (35%) of individuals classified as "high risk" because of a score greater than 5 had significant stenosis, while 20% of those at "intermediate risk" (score 3 to 5), and 7% of those at "low risk" (score less than 3) had significant stenosis.
Individuals asymptomatic for carotid artery disease atherosclerosis but screened for stenotic lesions because of other forms of vascular disease have prevalence rates of carotid atheromas that are higher than in the general population. Individuals with symptomatic coronary artery stenosis in one vessel have an almost 15% prevalence of significant carotid artery stenosis (greater than 50% stenosis). With two-vessel coronary artery stenosis, the prevalence is 21%, and with three-vessel coronary artery stenosis, the prevalence is 36%.27 The prevalence of significant carotid artery stenosis (greater than 50% stenosis) is 46% in patients having hemodynamically significant renal artery stenosis28 and 18% for individuals requiring the surgical repair of an abdominal aortic aneurysm.29
The prevalence of significant carotid artery stenosis (greater than 50% stenosis) in individuals with peripheral vascular disease is dependent on the number of associated risk factors (age older than 70, diabetes mellitus, history of stroke, and an ankle/brachial (ABI) test score index of less than 0.8).30 The prevalence of stenosis is: 16%, 21%, 38%, 47%, and 44% for patients with no, one, two, three, and four risk factors, respectively. The ABI test is performed by measuring blood pressure at the ankle and in the arm while a person is at rest. A normal resting ABI is 1 or 1.1 and means that the blood pressure in the ankle is the same or greater than the pressure in the arm and that there is no significant peripheral artery disease. A resting score less than 1 is abnormal and, depending on the magnitude, may indicate peripheral artery disease. A second component of the test requires that the patient complete 5 minutes of walking on a treadmill. A decrease in the ABI result with exercise is a sensitive indicator that significant peripheral artery disease is present.31
The associations between extracranial carotid artery disease and other forms of vascular disease are not unexpected given the shared risk factors (age, high levels of LDL cholesterol, elevated triglycerides, diabetes, hypertension, low levels of HDL cholesterol, cigarette smoking, and increased body mass index).32,33 Furthermore, atherosclerosis is often generalized within the same individual.34,35
Knowledge of the ASN Practice Guidelines can serve to heighten a dentist’s suspicions that a radiopacity in the region of the carotid artery bifurcation may be an atheroma. Consistent with the American Dental Association’s Council on Scientific Affairs, such patients should be referred to a physician for a comprehensive evaluation.
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The authors of this manuscript have provided us with an in-depth review of the literature on the dentistas role in the detection of carotid atheromas by panoramic radiography and its medical implications. As dentists we can save lives. Most of our patients only see a physician when they are sick. These same individuals come for routine dental check-ups: in most cases, twice a year.As dentists we have the opportunity to catch potentially serious medical conditions and make an appropriate referral.
A good example how dentists can be life-savers is the routine evaluation of blood pressure in the dental office. It has been more than 25 years since the recognition of the expanded role of dental panoramic radiographs in recognizing a potentially life-threatening medical condition. Calcified atherosclerotic lesions located in the bifurcation region of the carotid artery can lead to stroke for our patients. The article cites the fact that more than 700,000 Americans suffer a stroke each year with 275,000 of these individuals dying from this medical complication. This article points out the patients who are at risk for stroke due to atheromas, including patients who are older than 60, patients who have abused alcohol and tobacco, and patients with type 2 diabetes mellitus, metabolic syndrome, obstructive sleep apnea, or systemic illnesses associated with generalized atherosclerosis.When evaluating a panoramic radiograph, especially for patients at risk, the dental practitioner can note the presence or absence of radiopacities in the carotid bifurcation regions of dental panoramic radiographs. For patients at risk as well as other patients, the presence of radiopacities in this region should lead to a referral to the appropriate physician for further evaluation and treatment.-Howard E. Strassler, DMD
Arthur H. Friedlander, DMD
Associate Chief of Staff and Director of Graduate Medical Education
VA Greater Los Angeles Healthcare System
Los Angeles, California
Director of Quality Assurance, Hospital Dental Service
Medical Center at the University of California
Los Angeles, California
Professor-in-Residence, Oral and Maxillofacial Surgery
University of California Los Angeles School of Dentistry
Los Angeles, California
Allan G. Farman, BDS, PhD, MBA, DSc
Division of Radiology and Imaging Science
Department of Surgical and Hospital Dentistry
University of Louisville School of Dentistry
Clinical Professor of Radiology
Adjunct Professor of Anatomical Science and Neurobiology
University of Louisville School of Medicine