Carotid body tumor overview

# Overview
Carotid body tumor, also known as carotid body paraganglioma, is a neuroendocrine neoplasm originating from carotid body. It is located at the carotid bifurcation with characteristic splaying of the internal carotid artery and external carotid artery.

# Historical Perspective
Carotid body was first described by Von Haller in 1743. From 1930, it has been accepted that monitoring of arterial blood oxygen is its main function. Carotid body tumor was first described by Bungeler in 1952. The familial form of the carotid body tumor was first described by Chase in 1993. In 1889, The first surgical excision of the tumor without complication was done by Dr. Albert.

# Classification
Carotid body tumor is classified into sporadic, familial and hyper-plastic form. According to Shamblin surgical classification, carotid body tumor divided into three subtypes which includes: class I that localized with minimal vascular attachment, class II that partially surrounds carotids and class III which encases carotids as well.

# Pathophysiology
The carotid body is an ellipsoid-like structure located in the adventitia or periadventitial tissue of the bifurcation of the common carotid artery. This organ is a chemo-receptor and its function is the monitoring of arterial blood oxygen and carbon dioxide levels. The exact pathogenesis of carotid body tumor is not fully understood. however, the overgrowth of chemoreceptor paraganglioma cells in the carotid body leads to the formation of carotid body tumor. Recent litreture has suggested the role of several germline mutations in the pathogenesis of this tumor. Also, the hyperplastic form of the tumor has been associated with conditions that causes chronic hypoxia.

# Causes
Carotid body tumor may be caused by familial syndromes, germline mutation of several genes, or chronic hypoxia.

# Differentiating Carotid body tumor from Other Diseases
Carotid body tumor must be differentiated from other diseases that cause neck mass including schwannomas and lymphadenopathy.

# Epidemiology and Demographics
The incidence of carotid body tumor is less than 3 in 100,000 individuals. It is the most common paraganaglioma of the head and neck and comprises approximately 65% of paragangliomas. The prevalence of head and neck paraganglioma is 3% of all paraganglioma. This tumor is more commonly observed in the adults and particularly in their fifth decade of life. It affects both gender equally.

# Risk Factors
Common risk factors in the development of carotid body tumor include genetic mutation and chronic hypoxia.

# Screening
There is insufficient evidence to recommend routine screening for the carotid body tumor. However, patients who manifested the symptoms before the age of 50 years old, those with a positive family history and those with multiple paragangliomas has been recommended to undergo additional testing.

# Natural History, Complications, and Prognosis
If left untreated, patients with carotid body tumor may progress to develop cranial nerve dysfunction, airway obstruction, and malignant transformation of the tumor. Prognosis is generally good, and the 10-year survival rate of patients is approximately 50%.

# Diagnosis

## Diagnostic Study of Choice
The carotid body tumor is diagnosed primarily by history and physical examination. However, imaging studies are necessary to make the final diagnosis. Color Doppler ultrasound has been recommended as a method of screening for the diagnosis of carotid body tumor. It is also suggested that CT angiography is more accurate than color Doppler ultrasound for the diagnosis of larger lesions. CT imaging combined with color Doppler ultrasound has been suggested as the optimal detection modality for the assessment and management of the tumor. It should be mentioned that, traditionally, digital subtraction angiography (DSA) has been the gold standard for the diagnosis of carotid body tumor.

## History and Symptoms
The most common symptoms of carotid body tumor include neck mass, neck pain or headache. Other symptoms may also be present depending on the invasion of tumor to the neighboring structures.

## Physical Examination
Patients with carotid body tumor usually appear normal. Physical examination of patients with carotid body tumor is usually remarkable for a palpable, painless, rubbery mass at the lateral side of the neck.

## Laboratory Findings
There are no diagnostic laboratory findings associated with carotid body tumor. However, since these tumors originate from extra-adrenal chromaffin tissue of the autonomic nervous system, they may be capable of catecholamine productions.

## Electrocardiogram
There are no ECG findings associated with carotid body tumor.

## X-ray
There are no x-ray findings associated with carotid body tumor.

## Echocardiography and Ultrasound
The combination of B mode ultrasound imaging and color-Doppler sonography has been observed to be diagnostic for carotid body tumor.

## CT scan
Cervical CT scan may be helpful in the diagnosis of the carotid body tumor. Findings on CT scan suggestive of/diagnostic of carotid body tumor include a well-defined, hypervascular mass which will show homogeneous and intense enhancement after intravenous administration of contrast dye.

## MRI
MRI may be helpful in the diagnosis of carotid body tumor. Findings on MRI suggestive of/diagnostic of carotid body tumor is salt and pepper appearance on the T2 weighted images. On T1 weighted images, the tumor has the same intensity as the muscle.

## Other Imaging Findings
Since paragangliomas including carotid body tumor are of neuroendocrine origin, they may have somatostatin surface receptor which can be detected as an area of intense radio-tracer uptake by the Indium-111 octreotide scan. This modality may be helpful in the diagnosis of multicentric or metastatic disease. It also may be used after the surgery to look for a residual tumor.

## Other Diagnostic Studies
There are no other diagnostic studies associated with carotid body tumor.

# Treatment

## Medical Therapy
There is no treatment for carotid body tumor; the mainstay of therapy is surgery.

## Surgery
Traditionally, surgery is considered the mainstay of treatment for the carotid body tumor. However, there is a growing amount of studies observing that radiotherapy can be used as an alternative treatment with equal efficacy and lower complications.

## Primary Prevention
There are no established measures for the primary prevention of carotid body tumor.

## Secondary Prevention
There is insufficient evidence to recommend routine screening for the carotid body tumor. However, patients who manifested the symptoms before the age of 50 years old, those with a positive family history and those with multiple paragangliomas has been recommended to undergo additional testing.