Carotid body aneurysms are chemoreceptor tumors. The chemoreceptors are mainly found in the carotid body and the aortic body. These tumors are relatively uncommon. Since it was first described by Vou Haller in 1743, nearly 1000 cases have been reported worldwide so far. About 150 cases have been found in China.
1.Symptoms and diagnosis
Most of the patients usually visit the clinic with a neck mass and usually have no uncomfortable symptoms. However, a few patients have syncope, tinnitus, blurred vision and other manifestations of impaired blood supply to brain tissue. If the ninth, tenth, eleventh and twelfth pairs of cerebral nerves are compressed, dysphagia, hoarseness, ipsilateral displacement of tongue tip when tongue is extended and Horner syndrome may occur. If the tumor grows towards the pharynx, pharyngeal bulge may be detected during oral examination. About 3% of patients with carotid body tumor may have carotid sinus syndrome, which is an allergic reaction of carotid sinus caused by tumor compression of carotid body. The main manifestation is the suppression of cardiac function. Patients may suddenly experience slow heartbeat and drop in blood pressure, leading to cerebral ischemia and hypoxia and fainting. On physical examination, the aneurysm is located in the carotid triangle and appears as an ovoid mass, which can be pushed from side to side but not from top to bottom, with a smooth surface and moderately soft texture. On auscultation, a vascular murmur can be heard. The diagnosis is generally not difficult. When a substantial mass at the bifurcation of the common carotid artery below the angle of the jaw is palpated, sometimes with pulsation, tremor and murmurs, and the mass is slightly reduced by compression of the proximal common carotid artery, it can usually be considered. Color ultrasonography can help detect this disease. In contrast, selective carotid angiography provides a definitive diagnosis.
The angiographic diagnosis of carotid body aneurysm has the following features.
(1) Cup-like enlargement of the bifurcation angle of the internal and external carotid arteries.
(2) Abundant fine vessels within the tumor.
(3) The blood supply of the tumor mainly comes from the bifurcation area of external carotid artery and common carotid artery.
2.Differential diagnosis
(1) Carotid sympathetic nerve sheath tumor
Carotid body tumor is most easily confused with carotid sympathetic nerve sheath tumor. A deep carotid body aneurysm can often compress the carotid sympathetic nerve and lead to Horner’s syndrome, while a high carotid sympathetic nerve sheath aneurysm can also grow toward the pharynx.
(2) Carotid artery bifurcation dilatation
This is a mild dilatation of the carotid bifurcation area, which is easily misdiagnosed as carotid body aneurysm or carotid artery aneurysm. It is most often seen in middle-aged and elderly people and can be differentiated by experienced vascular surgeons in general. When the proximal common carotid artery is compressed, the dilated area may immediately shrink or disappear. No special treatment is usually required.
(3) Carotid aneurysm
Both have pulsatile masses in the neck, so they are easier to confuse. However, when compressing the proximal carotid artery, the masses shrink significantly as carotid aneurysms, and those that do not shrink significantly as carotid body aneurysms. Carotid artery angiography can be used to make a clear diagnosis.
(4) Neck masses
Tumors of the neck, such as cervical nerve sheath tumor or neurofibroma, parotid gland tumor, malignant lymphoma, parotid laceration cyst, etc. can all appear as neck masses, the former being solid masses and the latter being cystic.
3.Etiology and pathology
The etiology is unclear. There is usually no family history of unilateral lesions, but most bilateral carotid body aneurysms can have a family history. It has been found that the incidence of carotid body aneurysm is relatively higher in the plateau area of 2000~4000 meters above sea level; this may be due to the chronic ischemic condition in the plateau area that stimulates the carotid body to cause tissue proliferation, thus gradually growing into tumor.
The tumor form can be divided into two types: one is the confined type, which is located in the outer sheath of the carotid bifurcation; the other is the encapsulated type, which is more common. The tumor is located at the bifurcation of the common carotid artery and grows around the encapsulated common, internal and external carotid arteries, and does not involve the middle layer and intima of the carotid artery. However, the tumor may enlarge and compress the carotid artery and cause cerebral ischemia. Sometimes the tumor may involve the surrounding tissues such as the internal jugular vein and the ninth, tenth, eleventh and twelfth pairs of cerebral nerves, resulting in corresponding symptoms.
The tumor has no obvious envelope and is an oval or irregular shaped tiny pink tissue with medium texture and rich trophoblastic vessels. The blood supply mainly comes from the external carotid artery and returns through the pharyngeal and lingual veins, which are innervated by the glossopharyngeal nerve. Microscopically, the cells were nest-shaped and arranged around the vascular fibrous septum. Histological examination does not allow differentiation between malignant and benign. Lymphatic or distant metastases and local recurrence after resection are the main features of malignancy. Malignancy accounts for approximately 10% of cases.
4.Treatment
The main treatment is surgery, and there are two main types of surgery.
(1) Carotid aneurysm dissection: Although this surgical method does not block the carotid artery, it should be operated carefully to avoid damaging the carotid artery or other tissues.
(2) Tumor resection and carotid artery reconstruction: This procedure requires blocking the carotid artery, so care should be taken to prevent cerebral ischemia.