History
A 6-year-old 28.5-kg (62.7-lb) castrated male English Bulldog was referred to a veterinary teaching hospital for evaluation of a long-term history of regurgitation and stertorous breathing. The regurgitation began 2 to 3 months earlier and occurred at almost every meal, both during and after eating. The dog historically had increased upper respiratory sounds while breathing; however, the owners reported that these sounds had become much louder over the preceding 2 to 3 months. Results of neck and thoracic radiography and a barium study performed by the referring veterinarian indicated no abnormality in the trachea or esophagus.
On physical examination, no abnormalities were detected other than mild bilateral stenosis of the nares, moderate to severe stertor, and moderate generalized gingival hyperplasia. No clinically important abnormalities were detected on CBC or serum biochemical analyses. The dog was anesthetized, and a laryngeal examination revealed a severely elongated and moderately thickened soft palate, everted laryngeal saccules, and macroglossus, all typical findings of brachycephalic airway syndrome. For staphylectomy planning, CT of the dog's head and cranial neck region was performed with a 16-slice helical CT scanner. Images obtained before and after IV administration of contrast medium (iohexol [350 mg iodine/mL solution], 56 mL) revealed an unexpected unilateral mass in the cranial region of the dog's neck (Figure 1).
Transverse plane CT images of the cranial neck region of a 6-year-old 28.5-kg (62.7-lb) castrated male English Bulldog with a long-term history of regurgitation and stertorous breathing. Images obtained before (A) and after (B) administration of contrast medium are displayed in a soft tissue window (window width, 320 HU; window level, 30 HU), and the dog's right is to the left of the image.
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.467
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
On CT images, a soft tissue-attenuating, contrast-enhancing (45 HU before and 190 HU after administration of contrast medium) mass was identified adjacent to the right common carotid artery in the cranial region of the neck (Figure 2). The mass measured 4.2 × 4.0 cm in cross-section and mildly displaced the larynx and cranial portion of the esophagus to the left and displaced the right internal jugular vein, right common carotid artery, and right mandibular salivary gland to the right. On 3-D reconstruction, the mass was evident at the bifurcation of the right common carotid artery into the internal and external carotid arteries (Figure 3).
Same CT images as in Figure 1. There is a 4.2 × 4.0-cm, soft tissue-attenuating, contrast-enhancing mass (arrows; A and B) adjacent to the right common carotid artery (asterisk; B), and the mass mildly displaces the surrounding structures.
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.467
A 3-D reconstruction optimized for vasculature (red) shows the location of the highly vascular mass (arrows) lying medial to the right mandibular salivary gland (MSG) at the level of the common carotid artery bifurcation (asterisk).
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.467
Ultrasound-guided fine-needle aspiration of the mass was performed, and cytologic examination results were most consistent with a neuroendocrine tumor. When considered together, the anatomic location of the mass and the signalment and history of the dog were highly suggestive of a carotid body tumor.
Treatment and Outcome
A staphylectomy was performed without complications, and the dog's breathing remained normal throughout the next 24 hours. The dog was discharged the day following surgery. The owners declined an oncology consultation and elected palliative care and follow-up with their primary veterinarian. The patient was lost to follow-up.
Comments
The carotid bodies are groups of chemoreceptors at the main bifurcations of each common carotid artery (located bilaterally just caudal to the angle of each mandible). The carotid bodies are part of a larger network of peripheral neuroendocrine chemoreceptors that sense changes in blood gasses (primarily oxygen and carbon dioxide) and pH and help regulate respiration and circulation.1 Carotid body tumors tend to be unilateral, slow-growing, mostly benign but locally invasive, highly vascular, and nonfunctional.1 In animals, carotid body tumors are most common in dogs, particularly in brachycephalic breeds (eg, Bulldogs, Boston Terriers, and Boxers).1 The cause of carotid body neoplastic transformation is hypothesized to be exacerbation of genetic predisposition by prolonged stimulation of the chemoreceptors by chronic hypoxia and hypercapnia (alone or in combination) induced by upper respiratory anatomic abnormalities present in brachycephalic airway syndrome.1 Affected dogs may also have concurrent aortic body tumors,1 and although carotid and aortic body tumors are rare, their true prevalences are likely underreported.
Definitive diagnosis of carotid body tumors can be challenging. Patient signalment and history combined with results of physical and radiographic examinations can suggest a carotid body tumor; however, no definitive conclusions can be drawn, other than the presence of an abnormal mass in the neck of an affected dog. Further, a slow-growing mass just caudal to the angles of the mandibles in a dog may or may not be palpable externally. In human medicine, various advanced imaging modalities (eg, ultrasonography, angiography, MRI, CT, and positron emission tomography) are used in diagnosing carotid body tumors.2 In dogs, ultrasonography, CT, and MRI have been used for diagnosis of carotid body tumors,3–5 and clinically normal ultrasonographic appearances of necks and masses in necks of dogs have been reported.6,7 Images obtained with CT and MRI can provide excellent detail about tumor characteristics (eg, size, shape, exact location, degree of vascularity, and invasiveness), be used to make 3-D reconstruction images, and detect the presence of metastasis or concurrent aortic body tumor. Computed tomography and MRI in veterinary medicine are relatively expensive, require general anesthesia, and often require referral, whereas ultrasonography is relatively inexpensive, is more readily available, and can be used to guide fine-needle aspiration of such masses. Nonetheless, cytologic examination results for samples must be interpreted with caution, and the presence of a carotid body tumor must not be inferred solely on the basis of presence of a neuroendocrine pattern. Definitive diagnosis of a carotid body tumor is on the basis of histologic evaluation with special stains because other masses (eg, thyroid tumors) can have nearly identical imaging or cytologic characteristics.
The presumed carotid body tumor in the dog of the present report could have been partially responsible for the dog's regurgitation and upper respiratory compromise because, as a space-occupying lesion, it pressed on the esophagus and trachea and could have created obstructions for the passage of food and air, respectively. Other differential diagnoses for the dog's regurgitation included a sliding hiatal hernia and esophageal anatomic or motility disorders. With growth of the mass in the dog of the present report, signs of circulatory or neurologic complications could have developed.1
References
1. Rosol TJ, Gröne A. Endocrine glands. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's pathology of domestic animals. Vol 3. 6th ed. St Louis: Elsevier, 2016;269–357.
2. van den Berg R. Imaging and management of head and neck paragangliomas. Eur Radiol 2005;15:1310–1318.
3. Fife W, Mattoon J, Tod Drost W, et al. Imaging features of a presumed carotid body tumor in a dog. Vet Radiol Ultrasound 2003;44:322–325.
4. Kromhout K, Gielen I, De Cock HE, et al. Magnetic resonance and computed tomography imaging of a carotid body tumor in a dog. Acta Vet Scand 2012;54:24.
5. Mai W, Seiler GS, Lindl-Bylicki BJ, et al. CT and MRI features of carotid body paragangliomas in 16 dogs. Vet Radiol Ultrasound 2015;56:374–383.
6. Wisner ER, Mattoon JS, Nyland TG, et al. Normal ultrasonographic anatomy of the canine neck. Vet Radiol 1991;32:185–190.
7. Wisner ER, Nyland TG, Mattoon JS. Ultrasonographic examination of cervical masses in the dog and cat. Vet Radiol Ultrasound 1994;35:310–315.
