Carotid body tumor

Changed by Dr Anuj Aggarwal, 30 Nov 2020
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Carotid body tumour, also known as a chemodectoma or carotid body paraganglioma, is a highly vascular glomus tumour that arises from the paraganglion cells of the carotid body. It is located at the carotid bifurcation with characteristic splaying of the ICA and ECA. 

Epidemiology

Typically, carotid body tumours are diagnosed in the 4th to 5th decades, and have a female predilection like the other paragangliomas of the head and neck 1,3. They are the most common type of paraganglioma of the head and neck (account for 60-70%). In approximately 10% of cases, they are bilateral 1,3.

A small number are familial (7-10%), and in such cases, they are frequently multicentric (35-50%) 1,3. When familial, they are usually autosomal dominant in inheritance, and associated with 3:

Clinical presentation

Clinical presentation is usually with a slow growing rounded neck mass. It is usually located anterior to the sternocleidomastoid near the angle of the mandible at the level of the hyoid bone. Characteristically, the tumour can be moved side to side but not up or down, due to its location within the carotid sheath 1. 

Cranial nerves that travel in the carotid sheath (glossopharyngeal, vagus, accessory and hypoglossal nerves) may be involved. Associated symptoms relate to their dysfunction 2. 

These tumour may synthesise and secrete catecholamines, although this is less common than with adrenal paragangliomas (pheochromocytomas) 1.

Pathology

The paraganglioma article includes a general discussion of the pathology of these tumours.

Radiographic features

Carotid body tumours are located at the carotid bifurcation with characteristic splaying of the ICA and ECA, described as the lyre sign. In all modalities, the dense vascularity of these tumours is manifested as prominent contrast enhancement.

CT

Contrast-enhanced CT is excellent at depicting these lesions. Typical appearances are:

  • soft tissue density on non-contrast CT (similar to muscle)
  • bright and rapid (faster than schwannoma) enhancement
  • splaying of the ICA and ECA
  • We can mention the circumferential angle of contact of tumor with ICA and mention the Shamblin group (Group I with <180 degree, Group II: 180-270 degree and group III with >270 degree encasement). This helps in deciding the risk of ICA adventitial involvement and possible need of ICA resection followed by grafting required in group III cases.4
MRI
  • T1
    • iso to hypointense compared to muscle
    • salt and pepper appearance when larger, representing a combination of punctate regions of haemorrhage or slow flow (salt) and flow voids (pepper) 3
    • intense enhancement following gadolinium
  • T2
    • hyperintense compared to muscle
    • salt and pepper appearance also seen on T2
DSA/angiography

The splaying of the carotid vessels (lyre sign) is again identified with an intense blush in tumour with and 'early vein' seen due to arteriovenous shunting 3.

The ascending pharyngeal artery is the main contributing supply.

Scintigraphy

Although not specific, shows uptake with metaiodobenzylguanidine (MIBG) and octreoscan scintigraphy and can be useful for assessing multiple lesions.

Treatment and prognosis

Surgical excision is the treatment of choice. The larger the tumour the higher the risk of operative complications 2. In patients for whom the risk of complications precludes surgery, radiotherapy may be considered 1-2.

Malignant transformation is encountered in 2-36% of cases with metastases most commonly to bone, lung and liver and regional lymph nodes 3.

Differential diagnosis

General imaging differential considerations include:

  • +<li>We can mention the circumferential angle of contact of tumor with ICA and mention the Shamblin group (Group I with &lt;180 degree, Group II: 180-270 degree and group III with &gt;270 degree encasement). This helps in deciding the risk of ICA adventitial involvement and possible need of ICA resection followed by grafting required in group III cases.<sup>4</sup>
  • +</li>

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