Carotid Body Tumors

What Is Carotid Artery Function?

Most paraganglia within the head and neck region are associated with the normal functions of the parasympathetic nervous system. The most common site of extra-adrenal paragangliomas usually arises within the bifurcation of the external and internal carotid arteries. Apart from being the major blood suppliers to the brain, neck, and face, these carotid arteries are also situated bilaterally in the neck region. Like most major arteries, the carotid artery comprises three tissue layers, namely,

1. The smooth inner layer (intima).

2. The muscular middle layer (media).

3. The outer layer (adventitia).

The carotid sinus is a significant branch point where this artery undergoes the most widening and is also referred to as the carotid bulb. The bulb or sinus has receptors or sensor regulators for blood pressure. It is the same pulse of this arterial supply that is felt in the neck region for physicians to check the pulse (with physicians' fingertips usually pressed against the trachea region of the neck).

The Von Hippel Lindau syndrome and neurofibromatosis type 1 are also identified to poise a genetic or hereditary inheritance in patients suffering from carotid body tumors (CBTs). Most paragangliomas apart from CBTs are usually traced to a congenital or hereditary form of tracing familially though more evidence is needed to prove it in literature.

What Is the Clinical Significance of Carotid Body Tumors?

A weak spot, area, or an inflamed or narrowed region in the carotid artery can lead to life-threatening medical conditions like carotid artery vasculitis, embolism, stenosis, stroke, and hypersensitivity. As the carotid bulb receptors function to regulate blood pressure which is the vital sign of human consciousness, the conditions arising in the carotid artery can be life-threatening and severe.

Also, CBTs can be due to a range of causative factors from autoimmune diseases to atherosclerosis, or blood pressure-related conditions. The vascular tumors arising within the carotid artery can be very challenging for both the physicians and the patient because of the significant and extensive vascularity of the artery. Although it is estimated that less than 10 % of carotid body tumors may be malignant, studies show the rate of cancerous potential or malignancy maybe upto 50 % in the affected patients. Most cases are evidence of negligence by the patient as the clinical symptoms of these tumors may be ignored for years together, given the slow growth and painless clinical presentation of the tumors.

On clinical examination by the physician, who mainly recognizes this tumor by the apparent "Fontaine" sign -wherein the tumor mass appears vertically fixed over the bifurcation of the common carotid artery. CBTs are commonly associated with vagal body tumors and cranial nerve palsy. 10% of patients suffering from CBTs may not realize they suffer from it till they are diagnosed with the paralysis of spinal accessory, hypoglossal, glossopharyngeal, or recurrent laryngeal nerves.

The clinical features of these tumors though they may be unnoticed for a long time, are mainly pain, hoarse voice, dysphagia (difficulty swallowing food), and shoulder drop. The compression of the artery as the tumor enlarges may create further clinical symptoms like the paresis of the tongue (impairment of tongue muscles or movements).

What Is the Differential Diagnosis of Carotid Body Tumors?

Before confirming CBTs, these other conditions should be cross-checked by the physician:

• Meningioma.

• Schwannoma.

• Thyroid gland trabecular adenoma.

• Neuroendocrine carcinoma.

• Middle ear adenoma.

• Thyroid carcinoma.

Though histologic differentiation of these lesions is challenging, immunohistochemistry and microscopic analysis by the pathologist will help in a precise diagnosis of these lesions, which show distinctive histologic patterns. The differential diagnosis for these lesions can be established by examining the lesion mainly based on the location or occurrence point in the neck. However, the gold standard for diagnosis remains the MRI (magnetic resonance imaging) scan of the carotid artery, thus reflecting the tumor upon radiographic imaging.

What Are the Histological and Radiographic Features of Carotid Body Tumors?

Radiologically on an MRI accompanied by contrast imaging (as contrast enhances the vascular component of these lesions), the tumors display a characteristic salt-and-pepper appearance with low signal and high signal foci of hemorrhage within the internal or external carotid artery. Some physicians also recommend nuclear imaging scans to clearly differentiate the tumor using the somatostatin analog called indium 111-octreotide, mainly for tumor detection of more than 1. 5 cms that are seen as hypervascular masses.

CT angiography and catheter angiography may also be recommended to determine the same. However, octreotide nuclear detection is proper even post-surgery in these individuals to check for remnant tumors and scar detection after surgery. Histologically, the appearance of the "Zellballen" cell nest pattern in these well-differentiated tumors, with basophilic cytoplasm and hyperchromatic nuclei with scattered chromatin, is diagnostic of CBTs. In the later stages of this tumor, pathologically, the cells undergo extensive necrosis, increased mitotic activity, and S-100 protein loss.

How Are Carotid Body Tumors Managed?

The first preventive measure by the affected individual in recognizing the clinical features of CNT like pain, pressure, and compression in the neck region along with shoulder drop or blood pressure changes often helps in early diagnosis and detection of carotid body tumors by the physician (who mainly checks for the painless often undetected mass in the carotid artery region even at an early stage).

Pre-operative adrenergic blockade and surgical resection of these paragangliomas are the primary gold standard treatments though it would prove a challenging surgery in severe malignant widespread tumors. Though CBTs have a five to ten-year survival rate after resection of the lesion, the post-operative prognosis usually depends on early detection, prevention of recurrence (which is common) by frequent follow-up, and radiographic imaging of the carotid region. These patients do not usually require chemotherapy or radiation therapy as they are not significantly impactful in preventing the recurrence of the lesions.

Conclusion:

To conclude, carotid body tumors should be detected early, and physician guidance with proper diagnostic imaging and histochemical studies will ensure long-term survival rates for patients suffering from this severe neoplasm.