F FDG PET/CT Axial image
A 62-year-old female patient presented with abdominal lump. CT chest, abdomen and pelvis shows multiple abdominal nodal masses. Biopsy revealed B Cell lymphoma. Current investigation is a 18-F FDG PET/CT performed for response post-R-CHOP chemotherapy showing a 2cm hyper-metabolic right neck mass and multiple avid abdominal masses.
18F-FDG PET/CT : FDG avid, SUV-max 8, right neck lesion at the bifurcation of the common carotid artery measuring 2cm. Multiple hyper-metabolic left supraclavicular, mesenteric, para-aortic and iliac nodes with splenic deposits demonstrates different / higher activity compared to the neck mass, up to SUV-max 32 in the mesenteric nodal mass.
CT neck, chest, abdomen and pelvis: There is an enhancing ovoid shaped right neck mass which appears to be splaying the common carotid artery bifurcation.
Ultrasound neck performed to plan biopsy: Duplex ultrasound shows a highly vascularised solid hypoechoic mass in the area of the carotid bifurcation, with splaying of the bifurcation of the internal and external carotid arteries. Biopsy thus not performed.
MRI neck: The right neck mass shows low T1 signal and high T2 signal. Post contrast there is avid enhancement with low internal signal suggestive of flow voids.
Carotid body tumours, also known as paragangliomas or chemodectomas, are neuroendocrine neoplasms which arise near the carotid bifurcation within glomus cells derived from the embryonic neural crest . Paragangliomas usually are slow-growing and less than 10% are malignant . The carotid body is the most common site of occurrence . Predominantly cases are found in patients ranging from 50 to 70 years of age with a slightly higher prevalence in women . Approximately 40% are thought to be hereditary .
Carotid body tumour classically presents as a non-tender, insidiously enlarging neck mass in an asymptomatic patient  and incidentally found on imaging . Untreated, they will ultimately result in a progressive enlarging cervical mass involving and causing dysfunction of cranial nerves . There is an increased prevalence of head and neck paragangliomas with familial genetic syndromes such as von Hippel-Lindau disease (VHL), multiple endocrine neoplasia type 2 (MEN2), and type 1 neurofibromatosis (NF1) .
Paragangliomas are hyper-metabolic on FDG PET/CT [8,9] and potentially misinterpreted as false positive metastatic lymphadenopathy . On CT, they are highly vascular [3,10] and typically presents as a well-defined soft-tissue mass within the carotid space of the infrahyoid neck . On ultrasound, there is splaying of the bifurcation of the common carotid artery [3,5]. On MRI they have low signal intensity with standard spin-echo short repetition time (TR)/short echo time (TE) and long TR/short TE sequences and a high signal intensity with long TR/long TE sequences. There is intense enhancement post administration of intravenous contrast [3,5]. If suspected, nuclear medicine tests such as Octreotide and I-123 MIBG SPECT/CT may be performed.
There is good prognosis with surgical treatment . A multidisciplinary team treatment approach is essential. Accurate imaging assessment for the anatomy and preoperative embolisation of large, vascular tumors can facilitate surgical treatment [1,2,6].
Take Home Message / Teaching Points
1. Carotid body tumours are most commonly located at the bifurcation of the common carotid arteries and are characteristically hypervascular in nature.
2. Paraganglioma is an important differential for neck masses to avoid erroneous interpretation of cervical lymphadenopathy.
3. Meticulous evaluation of a hyper-metabolic lesion on FDG PET/CT is essential, remembering causes of false positive findings including synchronous tumours, benign tumours, inflammation, infection, brown fat and physiological uptake [12,13].
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