Laboratory Studies
Check urinary catecholamines in patients who have any symptoms of a functional carotid body tumor. Routine assessment in all patients is common practice in many centers.
Imaging Studies
Various imaging studies can be used to confirm the diagnosis of carotid body tumor (CBT), starting with simple ultrasonography with color Doppler, which can assess the vascularity of the neck mass and can sometimes reveal a possibility of a carotid body tumor, although it is not the best imaging modality to detect these tumors. [2]
Computed tomography (CT) scanning of the head and neck is also helpful and typically reveals a hypervascular tumor located between the external and internal carotid arteries.
Magnetic resonance imaging (MRI) is considered to be the criterion standard for carotid body tumors, and the tumor has a characteristic salt and pepper appearance on T1-weighted image.
Magnetic resonance angiography (MRA) provides better insight into the vascularity of the tumor and its feeder vessels. [2] However, accurate diagnosis is usually based on angiographic criteria, which show the typical lyre sign. Angiography is also helpful for better visualization of the feeder vessels and is of utmost importance for high-risk tumors (Shamblin II or III) that need either embolization or a preoperative balloon occlusion test.
In patients who are suspected to have multiple small tumors, such as those with familial carotid body tumors (CBTs), performing a physical examination and supplementing it with imaging studies (including a CT, MRI, or metaiodobenzylguanidine [MIBG] scintigraphy) is essential. MIBG scans are quicker to perform than MRI and are also used in patients who are claustrophobic. The only issue with this scan is that it can only be used in patients who have functional tumors. In cases in which the tumor is nonfunctional, a better test is a pentetreotide scan, which uses a radiolabeled somatostatin analogue.
A study by Straughan et al indicated that preoperative imaging results showing a distance from the tip of the C2 dens to the superior aspect of the carotid body tumor of under 3 cm suggests an increased likelihood of perioperative cranial nerve injury. The study included 19 patients (20 carotid body tumor resections). [26]
Diagnostic Procedures
Because of its classic radiographic and clinical picture of hypervascularity and location between the arteries, incisional biopsy of carotid body tumors (CBTs) is not indicated and should not be performed except in very unusual cases. [2] Inadvertent biopsy may lead to profuse bleeding and/or cranial nerve injuries. [27]
Fine-needle aspiration biopsy is helpful only if the diagnosis is unclear via imaging studies.
Histologic Findings
Carotid body tumors (CBTs) are highly vascular tumors composed of the following 2 cell types that are arranged in a pseudoalveolar pattern characteristic of paragangliomas known as "cell balls" (zellballen): [16]
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Type I cells, which are the chief cells that predominate in carotid body tumors (CBTs) and contain catecholamine-bound granules
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Type II cells, which are the sustentacular cells located at the periphery, are devoid of granules
Paragangliomas are classified into noninvasive, locally invasive, and metastatic types. Unfortunately, malignancy cannot be detected by routine histological findings and is only defined when the tumor metastasizes to regional lymph nodes or more distant sites.
Nuclear polymorphism, neurovascular invasion, high mitotic indices, and necrosis may be present in both benign and malignant carotid body tumors (CBTs). [16]
Staging
Shamblin describes 3 different types or stages of carotid body tumors. Type I consists of a small tumor that is easily dissected from the adjacent vessels in a periadventitial plane. Type II tumors are larger and more adherent and partially surround the vessel. Type III tumors are large and completely surround the carotid bifurcation. [28] As described, types II and III tumors are more likely to require carotid resection.
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Proximal and distal control of the carotids with vessel loops.
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Complete subadventitial removal of the tumor with intact carotids.
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Carotid body tumor after total excision.
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CT scan with IV contrast demonstrating a large left enhancing carotid body tumor extending into the parapharyngeal space to the oropharynx.
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Preauricular excision extended from the neck in patients who have large tumors.
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Proximal and distal control of the carotids is extremely important and can be difficult in larger tumors.
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Postoperative picture after removal of the tumor.
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Four-vessel angiography of a 57-year-old patient with bilateral carotid body tumors.
