Carotid Body Tumor Masquerading as Metastatic Cervical Lymph Node on Fluorodeoxyglucose Positron-emission Tomography-Computed Tomography

A 56-year-old male patient presented with swelling in the left side of the neck for the past 2 months. He had a previous history of squamous cell carcinoma of left pyriform sinus which was treated with chemoradiotherapy 5 years back. In view of the previous history of carcinoma left pyriform sinus, a provisional diagnosis of metastatic cervical lymphadenopathy has been made. Subsequently, the patient has been referred for fluorodeoxyglucose positron-emission tomography-computed tomography (FDG PET/CT) for further assessment. FDG PET/CT study revealed a hypermetabolic soft-tissue density nodule measuring approximately 2.2 cm × 2.5 cm in the bifurcation of the common carotid artery (maximum standardized uptake value 10.2) [Figure 1a, c, and e]. No other areas of focal tracer uptake noted in rest of the body [Figure 1g, MIP image]. However, on further careful evaluation of the contrast-enhanced CT part, it was noted that the lesion has similar enhancement such as a carotid artery with splaying of carotid bifurcation [Figure 1b, d, and f]. On the basis of typical location and characteristic imaging findings, a provisional diagnosis of carotid body tumor was made. Subsequent neck exploration was performed with careful dissection of the lesion. Histopathological evaluation was subsequently reported as paraganglioma.

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Figure 1 Fluorodeoxyglucose positron-emission tomography-computed tomography study revealed a hypermetabolic soft-tissue density nodule measuring approximately 2.2 cm × 2.5 cm in the bifurcation of the common carotid artery (maximum standardized uptake value 10.2) (a, c and e). No other areas of focal tracer uptake noted in rest of the body (g, MIP image). However, on further careful evaluation of the contrast-enhanced computed tomography part, it was noted that the lesion has similar enhancement such as carotid artery with splaying of carotid bifurcation (b, d, and f)

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Carotid body tumors (CBTs) are rare, benign neoplasms that originate from the neuroectodermal paraganglion. Originating from the afferent ganglion of the glossopharyngeal nerve, carotid body tumors are generally located at the carotid bifurcation.[1] Physiological activity is rare in these neoplasms, and these tumors generally exhibit a slow rate of growth, most often presenting asymptomatically as a space-occupying mass lesion noted clinically or radiographically.[12] They can occur sporadically or as inherited familial tumors. Patients with multiple endocrine neoplasia type 2, von Hippel–Lindau disease, or neurofibromatosis type 1 are prone to head and neck PG. Approximately 30% of apparently sporadic head and neck PGs are associated with germline mutations in the mitochondrial complex II genes. The described mutations in SDHB, SDHC, and SDHD genes cause one out of four paraganglioma syndromes with similar clinical features.[3] 18F-Fluorodeoxyglucose (¹⁸F-FDG) uptake in these tumors is strongly dependent on patient genotype. Increased ¹⁸F-FDG uptake in these tumors can be used clinically to help identify patients in whom SDH mutations should be suspected.[45] The differential diagnosis of carotid body tumor includes cervical lymphadenopathies, branchial cleft cysts, salivary gland tumors, schwannomas, and aneurysms of the carotid artery.[36] Since both CBTs and metastatic cervical lymph node can be FDG positive it was easier to overlook the possibility of a CBT in the present case for the preoccupation of neck metastasis from carcinoma of the left pyriform sinus. Considering the splaying of the carotid bifurcation and similar enhancement as carotid artery revealed by the contrast-enhancing CT scan, we, fortunately, suspected the possibility of left-side CBT. This unique case further signifies the importance of performing contrast-enhanced CT scan as an adjuvant tool with FDG PET imaging, especially in case of head and neck malignancies. Apart from accurate localization of the lesion, it can also help in differentiating different clinical entities mimicking as lymph nodal metastases in case of head and neck malignancies.