Carotid body tumour

A 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 4^th to 5^th 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:

• multiple endocrine neoplasia : MEN IIa and MEN IIb
• phakomatoses
  • tuberous sclerosis complex (TS)
  • neurofibromatosis type 1 (NF1)
  • von Hippel-Lindau disease (vHL)
• Carney triad

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 (vagus, glossopharyngeal, 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

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 :
  • hyper intense 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 preclude 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

• vagal schwannoma : tends to displace both vessels together rather than splaying them
• vagal neurofibroma : tends to displace both vessels together rather than splaying them
• lymph node mass : may look similar if hyper-vascular
• glomus vagale tumour : same pathology but located more rostrally
• carotid bulb ectasia