Cone Beam CT of Carotid Artery Densities
Robert A. Danforth, DDS; Edward E. Herschaft, DDS, MA
Cone Beam CT
This case report describes the history and significance of regional neck calcifications commonly observed on panoramic and cone beam (CB) CT radiographs in dental practice. CBCT is a low-dose cross-sectional technique for visualizing bony structures in the head and neck and is increasingly used for point-of-service head, neck, and dentomaxillofacial imaging.Imaging characteristics and differentiation of anatomic regional neck hyperdensities from calcified carotid artery atheroma (CCAA) are discussed in this case. Proper identification and assessment of these calcifications can assist the clinician in determining appropriate medical referral and dental management for the patient.
CCAA on Dental Radiographs
In 1981 Friedlander and Lande reported the ability to observe CCAA plaques on panoramic radiographs. In the sagittal plane, represented by the panoramic radiograph, these radiopacities were described as being located just superior to the carotid bifurcation and approximately 1.5-2.5 cm on a posterior incline from the angle of the mandible to a region adjacent to cervical vertebra C3-C5. CCAA must be differentiated from other anatomic and pathologic structures that may also be visible in this location (Figure 1).
Figure 1. Panoramic dental radiograph showing several bilateral oblong radiopacities of varied density (arrows).
The radiopacities appear to be superimposed on the outlines of the lower pharyngeal airway spaces and the anterior portions of the C3-C5 cervical vertebrae. These opacities are most likely the posterior portions of the greater horns of the hyoid bone and the partially calcified thyroid cartilage. However, in this location on panoramic radiographs, CCAA must be included in a differential interpretation of the image.
Significance of CCAA Findings
Subsequent reports[3-6] indicate that CCAAs are commonly discovered on panoramic radiographs and may be associated with systemic diseases, including stroke, hypertension, and type 2 diabetes. However, the diagnostic value of these observations remains controversial. The conclusions of other studies call into question the significance of CCAA on panoramic radiographs. For example:
Although CCAA discovered on panoramic radiographs may be related to previous vascular disease, it is not considered a useful marker for future vascular disease in 80-year-old individuals.
When compared with ultrasonography, panoramic radiography does not reliably detect CCAA. This finding supported the results of a previous study indicating that ultrasonography screening should be recommended for patients with CCAA on panoramic radiographics.
In a literature review of 54 studies, Mupparapu and Kim concluded that, "data supporting the hypothesis that radiographically detectable CCAA is associated with an increased risk of stroke are incomplete and inconclusive. Further research is needed, as clinical guidelines for risk prediction using panoramic radiographs cannot be established on the basis of the current evidence."
Among dental patients, a history of obesity, smoking, and hypertension might provide more correlative information about the potential for an acute vascular event than CCAA observed on panoramic radiographs.[11-13]
Although first used clinically in 1982, CBCT technology did not become commercially available in the United States until 2001. CBCT technology allowed dental practitioners to visualize CCAA densities in the 3 orthogonal projections (coronal, axial, and sagittal) (Figure 2).
Figure 2. Composite view of selected cone beam CT images shows bilateral linear and curvilinear hyperdense masses at the level of the larynx. Note: These are positioned lateral to the lower pharyngeal airway and cervical spine. These findings are interpreted as being consistent with external carotid artery calcifications.
The dentist reviewing CBCT images should have an understanding of the anatomic positions in which CCAA lesions appear. Other anatomic and pathologic hyperdensities can be differentiated from CCAA in these views.
Anatomic and Pathologic Hyperdensities of Interest
Several studies describe the panoramic radiographic appearances and locations of the stylohyoid ligament complex,[15,16]calcified triticeous cartilage,[17,18] and ossified laryngeal cartilages. When these anatomic structures become calcified, they might be confused with CCAA. Additionally, pathologic calcifications of the palatine tonsillar region have been described. The 3 most common soft tissue calcifications observed on CBCT images have been identified as CCAA, calcification of the triticeous cartilage, and calcifications of the tonsil.[20,21]
Scarfe and Farman describe the relationships between CBCT images of CCAA and calcifications of the stylohyoid chain, superior cornu of the thyroid cartilage, triticeous cartilage, and tonsil. Figures 3 and 4 illustrate some of these associations observed in coronal, axial, and sagittal CBCT images and reconstructed models.
Figure 3. Reconstructed visual models showing configurations and locations of bilateral curvilinear hyperdense masses interpreted as being consistent with external carotid artery calcifications.
Figure 4. Comparative views of selected reconstructed axial, coronal, and sagittal visual models created from cone beam CT images. Note: Arrows in Figure 4 identify anatomic opacities that should be differentiated from calcified carotid artery atheroma (CCAA). The upper composite series of selected hyoid and thyroid images highlights the superiorly positioned hyoid bone and the partially calcified thyroid cartilage with its prominent posterior cornu (horns) projecting toward the hyoid bone. The lower axial carotid views show the presence of CCAA, which are curvilinear hyperdensities laterally positioned to the midline curvature of the hyoid bone and the lateral extensions of the cervical vertebrae.
Bilateral Carotid Artery Hyperdensities Observed on CBCT Radiographs: Case Reports
Patient 1, a 56-year-old man of European ancestry with a history of hepatitis B, hypertension, and coronary artery disease, presented to the general practice residency dental clinic saying, "I am missing several teeth and would like to replace them with dental implants." The patient was diagnosed with pericarditis in 2006 and had bilateral carotid stents placed in 2008. He was taking multiple medications for his systemic health conditions.
Intraoral examination revealed no mucosal soft tissue pathology. However, both dental arches exhibited numerous missing teeth bilaterally. As part of the diagnostic workup to assess the efficacy of dental implant placement in this patient, CBCT radiographs were obtained (Figures 5 and 6). These images revealed bilateral "meshlike," hyperdense areas consistent with carotid artery stents and surgical fixation clips. These CBCT radiographic findings are consistent with the patient's medical history of bilateral carotid artery stent placement in 2008.
Figure 5. A composite view of selected cone beam CT images of the patient in this case shows bilateral, somewhat symmetrical, hyperdense objects (arrows). Note: In the axial view, the objects have ring configurations, whereas in the coronal and right and left sagittal views, these objects appear as vertically aligned "meshlike" cylinders. Additionally, these cylinders are bordered by several small rectangular hyperdense objects. These findings are consistent with the presence of bilateral carotid artery stents and surgical fixation clips.
Figure 6. Selected reconstructed visual models of axial, coronal, and sagittal cone beam CT images from Figure 5 show improved visualization of the configurations and locations of the bilateral carotid artery stents (arrows).
The images in Figure 5 and 6 were compared with those from another patient (Patient 2) who exhibited bilateral hyperdense masses suggestive of CCAA on axial CBCT radiographs (Figure 7). The purpose of this comparison was to use the images of the stents observed in patient 1 to help pinpoint the location of the CCAA-like hyperdensities in patient 2 to the location of the carotid arteries. Measurements relating the positions of the CCAA densities to those of the carotid artery stents indicated similar lateral-horizontal distances of the calcifications from the sagittal midline. Similar distances along acute line-angles radiating from the posterior midpoint of the cervical vertebrae were also found for the CCAA densities and the stents. Thus, the anatomic locations of the carotid stents and those of the bilateral hyperdensities supported the interpretation of the latter as CCAA.
Figure 7. a. Axial cone beam CT images of patient 2 show bilateral hyperdense masses interpreted as being consistent with carotid artery calcifications. b. Bilateral carotid artery stents observed in patient 1. Comparison of the measurements obtained from these images indicates similar lateral-horizontal distances of the calcifications from the sagittal midline and similar distances along acute line-angles radiating from the posterior midpoint of the cervical vertebrae (arrows).
Summary: Next Steps
CBCT radiographic findings suggestive of CCAA may be associated with medical histories that include obesity, cardiovascular disease, hypertension, transient ischemic attack, stroke, hypercholesterolemia, type 2 diabetes, sleep apnea, and male gender. Although attempts to correlate CCAA with risk for a cardiovascular event have limitations, dental practitioners must be able to differentiate possible CCAA lesions from anatomic and pathologic structures that also appear as hyperdensities in the neck.
An understanding of the relationships and anatomic positions of hyperdensities that need to be distinguished from CCAA can be facilitated by CBCT because this radiologic technique offers visualization of suspected lesions in all 3 orthogonal projections. Despite the controversy concerning the prognostic value of these findings, dentists should inform patients about radiographic results suggestive of CCAA. Patients should be referred to their primary care physician, with copies of the radiographs, for appropriate medical evaluation and radiologic consultation. If the patient is not currently under a physician's care for known cardiovascular disease, the dentist should make every effort to ensure that the patient is referred to a physician for proper evaluation.
The authors wish to acknowledge the contributions of Dr. George McAlpine, Director of the General Practice Dental Residency Program at the University of Nevada Las Vegas-School of Dental Medicine in the preparation of this manuscript.
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