Magnetic resonance and computed tomography imaging of a carotid body tumor in a dog
© Kromhout et al; licensee BioMed Central Ltd. 2012
Received: 5 December 2011
Accepted: 16 April 2012
Published: 16 April 2012
A 5-year-old castrated male Labrador Retriever was presented to a referring veterinarian for a swelling in the neck region. Based on the results of histopathology, a carotid body tumor, was diagnosed. The dog was referred to a medical imaging unit for further staging and follow up. This report describes the magnetic resonance (MR) and computed tomographic (CT) appearance of a carotid body tumor.
KeywordsCT MRI Carotid body tumor Paraganglioma Chemodectoma
Chemodectomas or paragangliomas are tumors of chemoreceptor cells. In dogs they originate most commonly from the aortic or carotid bodies. Carotid body tumors appear less frequent  and are usually more malignant than aortic body tumors . These tumors are usually non-functional. Generally, they cause clinical symptoms late in the course of the disease, as they exert a space occupying mass effect on the surrounding structures. Carotid body tumors tend to splay the carotid bifurcation as they enlarge , and treatment is difficult. This report describes the magnetic resonance (MR) and computed tomographic (CT) appearance of a histological confirmed carotid body tumor.
A 5-year-old castrated male Labrador Retriever was presented to a referring veterinarian for a swelling in the neck region. On physical examination a hard, painless, not retractable spherical mass, the size of a golf ball (+/ 55cm), was palpated just caudally of the left mandibula, in the region of the mandibular lymph node. A fine needle aspiration was performed and the dog was placed on antibiotics pending the outcome. As cytology results were inconclusive, mainly consisting of necrotic cell debris, antibiotic therapy was stopped and it was decided to remove the mass for histopathological examination. During surgical exploration a second, more oval, 154cm mass, located caudally from the first one, was noticed. This caudal mass was left in place and no biopsy samples were taken from it.
To rule out additional metastasis survey thorax radiographs (lateral and ventrodorsal) were performed. No radiographic abnormalities were observed. Subsequently 3weeks after exploratory surgery the dog was send to the Department of Veterinary Medical Imaging and Small Animal Orthopaedics for a MR scan of the mandibular and cervical region and a CT scan of the thorax. The CT procedure was performed with a multi-slice helical CT scanner (GE Lightspeed QX/I; General Electric Co., Milwaukee, MI, USA) with the patient under general anaesthesia and in ventral recumbency. Images were obtained before and immediately after administration of 2ml/kg intravenous contrast medium (Ultravist 300; N.V. Shering S.A.). Both pre- and post contrast images revealed no abnormalities at the level of the thorax.
Treatment and follow up
To our knowledge this is the first report of the MRI and the CT appearance of a confirmed carotid body tumor in a dog. The most important differential diagnoses for cranial cervical masses are abcesses, thyroid hyperplastic or neoplastic nodules, enlarged retropharyngeal lymph nodes, salivary glands inflammation or neoplasias. Neuroendocrine tumors, although generally rare, should be considered as well.
A carotid body tumor is a type of chemodectoma or paraganglioma. These are tumors of the chemoreceptor organs which detect changes in arterial blood oxygen, carbon dioxide and pH. The carotid glomus and aortic body are the most common sides for development of chemodectomas in dogs . The site of origin can also involve the tympanic cavity and inferior vagal ganglion . The carotid body is located dorsal from the bifurcation of the common carotid artery. Carotid body tumors appear less frequent than aortic body tumors in dogs  and are more malignant . There is a predisposition for Boxers and other brachycephalic dogs . Clinical signs are usually caused by a mass effect of the growing neoplasia on the surrounding structures and by local invasion . They tend to interfere with swallowing, cause dyspnoea and circulatory disturbances. Diagnosis in dogs is possible via imaging techniques such as ultrasonography , computed tomography  and histological diagnosis. The diagnosis of a neuroendocrine tumor in this case is based on the immunohistochemical expression of chromogranin A and vimentin . Morphology of the neoplastic cells was suggestive for a carcinoma and more specific of neuroendocrine origin. However because of the high degree of pleiomorphism definitive diagnosis was only possible after immunohistochemical characterization.
In human medicine conventional ultrasound, color Doppler ultrasound, carotid conventional angiography (CA), axial tomography, magnetic resonance and magnetic resonance angiography, and computed tomographic angiography (CTA) are used to diagnose carotid body tumors . On MRI carotid body tumors are heterogeneous iso- to hyperintense on T1W SE-images and heterogeneous hyperintense on T2W SE-images [9–11]. Regions of low signal intensity (signal voids or flow voids) appear in the mass due to the presence of high flow of vessels. This gives a salt-and-pepper heterogenity on T2W SE images, which is characteristic for paragangliomas, [10–12] but can also appear in other hypervascular lesions such as thyroid carcinomas . The salt components are the high-signal regions which correspond with slow flow or hemorrhage and the pepper components are the multiple signal voids of vessels on both T1W- as T2W SE images. Post-contrast paragangliomas show typical homogeneous and intense enhancement because of their hypervascularity . These findings are consistent with the findings seen on the images of our patient. On CT images, a carotid body tumor manifests as a well-defined soft-tissue mass within the carotid space with a homogeneous intense contrast enhancement. Large tumors are frequently inhomogeneous with areas of necrosis and hemorrhages . These findings are also visible on our images and are similar to previous reports in dogs .
Metastases of carotid body tumors are present in approximately 30%  of the reported cases and tend to spread to regional lymph nodes, liver, lung, pancreas, kidneys and bones [2, 14–16]. There is reported in humans that these tumors, although slow growing, are capable of rapid enlargement and metastasis at any stage of their evolution. This is consistent with our findings, where metastasis in the lymph nodes and pancreas were detected.
MRI, CT and other imaging techniques, such as RX or echo, are very usefull to determine the extent of the disease. A full clinical workup is essential for further planning and prognosis of the disease. The preferred treatment for carotid body tumors is surgical removal. MR imaging is the method of choice for surgical planning of the tumors [8, 9]. In humans there is a surgical classification system to assess the resectability of carotid body tumors. Tumors are classified in three groups according to Shamblin et al.  and are based on the tumor size. Group I are small tumors which could easily be resected from the vessels, group II includes tumors that are intimately associated and compress carotid vessels, but that could be resected with careful subadventitial dissection and group III consists of tumors that are large and require total resection of the external and/or internal carotid artery. Cross-sectional imaging such as MR, because of the better soft tissue detail and higher contrast resolution than CT, can accurately predict the group and is essential for decrease of the perioperative mortality rate. Dogs with Shamblin group III tumors have a higher risk for perioperative death . Judging from our CT and MR images the tumor of this dog belongs to Shamblin group II. If surgery is not possible, radiotherapy is recommended. Radiation therapy as a primary treatment, has not been described in humans and in animals. Radiation therapy is used for local control of the tumor, to eradicate microscopic disease and eventually prevent further spreading. Radiotherapy is helpful in cases with unresectable lesions, in high-risk patients and as additional treatment for incompletely excised tumors or metastases .
Due to the specific localisation and high vascularity of the carotid body tumor, combined with the specific imaging characteristics, CT and especially MRI can be used as a primary diagnostic imaging technique and as a tool for presurgical planning and postsurgical assessment of dogs.
Written informed consent was obtained from the owner for publication of this report and any accompanying images.
Common Carotid Artery
External Carotid Artery
Internal Carotid Artery
Magnetic Resonance Imaging
Short T1 Inversion Recovery
- T1W SE:
T1-weighted Spin Echo
- T2W SE:
T2-weighted Spin Echo.
KK carried out the diagnostic imaging and is the main author of the paper. KVD did the clinical examination of the dog. HDC performed the histopathology and the post mortem examination of the dog. IG and HVB reviewed the draft and helped to write the final version. All authors read and approved the final manuscript.
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