Carotid body aneurysms originate from the carotid body and are a rare chemoreceptor tumor. The carotid body is located under the outer membrane of the posterior wall of the carotid bifurcation. It regulates the body’s respiratory and circulatory systems by sensing blood components such as partial pressure of oxygen, partial pressure of carbon dioxide, and changes in acidity and alkalinity. Carotid body aneurysms are derived from carotid body hyperplasia and are chemoreceptor aneurysms. Carotid body aneurysms are mostly benign, and malignant carotid body aneurysms are rare, accounting for about 5% to 12%. Malignant carotid body aneurysms are usually diagnosed on the basis of metastasis, which is mainly local lymph node metastasis, but may also metastasize to lung, bone, liver and other sites via blood flow. Most carotid body aneurysms are disseminated and may be familial. In the literature, it has been reported that 30% to 50% of carotid body aneurysms are familial, and females account for the majority of non-hereditary patients, while there is no significant gender difference in hereditary patients. Because of the insidious onset of the tumor and the lack of typical clinical features, early detection is not easy and diagnosis is difficult. Because of the rich local vascularity of carotid body tumor and the special growth site, which is located at the bifurcation of carotid artery, adjacent to and adherent to arteries, veins and cranial nerves, surgical resection of this type of tumor is very difficult. This disease is often misdiagnosed as cervical lymph node enlargement and operated on, which is called the “trap of vascular surgery”, and improper treatment often has serious consequences and even endangers patients’ lives. Diagnosis of carotid body aneurysm Carotid body aneurysm usually appears as a slow-growing upper neck mass, located below the angle of the jaw, round or oval in shape, with a moderately hard texture, smooth surface, and clear borders. The tumor often wraps around the carotid artery and grows outward, or it may grow inward to compress the trachea. The mass can be pushed from side to side, but not from top to bottom. On palpation, there is a sense of arterial pulsation, and some of them can be heard as vascular murmur. When the mass compresses the vagus nerve, it may cause reflex coughing: a few cases of sublingual nerve compression may result in atrophy of the affected lingual muscle and motor impairment. Due to the lack of typical clinical manifestations, it is easy to misdiagnose and should be clinically differentiated from nerve sheath tumors, neurofibromas, metastases, gill slit cysts, and lymph node tuberculosis. For painless masses located in the anterior cervical triangle with pulsation, the possibility of carotid body aneurysm should be considered and further imaging should be performed to clarify the diagnosis. Blind puncture biopsy should not be performed to avoid serious complications. Imaging is very important for the diagnosis of carotid body aneurysm. Color Doppler ultrasonography has a high specificity and sensitivity for the diagnosis of carotid body aneurysm, and is the most simple and non-invasive method to confirm the diagnosis of carotid body aneurysm. The typical ultrasound features of carotid body aneurysm are: a hypoechoic mass at the bifurcation of carotid artery, a heterogeneous internal echogenicity with still clear borders, an abundant color flow signal in the mass, a pulsatile arterial spectrum, and an increased displacement of the spacing between the internal and external carotid arteries; CT examination can determine the adjacent relationship between the tumor and the surrounding tissues and the depth of the encircling carotid artery, which is important for the development of surgical plan. The MRI/MRA examination is a high-density signal image within the tumor, which can show the relationship between the tumor and blood vessels and the invasion of the tumor to the skull base through multi-axial imaging and three-dimensional angiography, with higher accuracy and no radiological damage. It can also reduce bleeding during surgery by embolizing the trophoblastic vessels of the aneurysm. Treatment of carotid body aneurysm The best treatment for carotid body aneurysm is surgical resection, which should be actively performed once the diagnosis is clear. The earlier the surgery, the smaller the tumor, the easier it is to handle, and the lower the chance of surgical complications, especially cranial nerve and artery damage. The larger the tumor, the tighter the adhesion with the artery, the more difficult it is to remove it surgically. Shamblin classified carotid body aneurysms into three clinical types according to the extent of tumor involvement in the carotid artery: Type I is the limited type, in which the tumor is located in the outer sheath of the bifurcation of the common carotid artery, and the envelope is relatively intact, with close adhesion only to the bifurcation of the common carotid artery. The tumor is located in the bifurcation of the common carotid artery and grows around the common, internal and external carotid arteries, but does not involve the middle layer and intima of the vessel wall; Type III is a giant type, in which the tumor grows beyond the bifurcation of the carotid artery and causes the internal and external carotid arteries to be displaced or compressed outward, even compressing the trachea and esophagus, causing difficulty in breathing and swallowing. Type I and II account for about 45% of the total incidence of carotid body aneurysms,11 and type I accounts for about 55%. Preoperative evaluation of the cerebral collateral circulation, especially the traffic in the williss loop, should be performed. The specific surgical approach should be determined by the type of carotid body aneurysm. For type I and some type II patients, carotid body aneurysm dissection is recommended, while for type 11I and some type II patients, the tumor should be resected together with the internal and external carotid arteries and the internal carotid artery should be reconstructed with the autologous saphenous vein to minimize the dissection of the carotid artery. Intraoperative blood pressure is kept stable to ensure the perfusion of the brain. The injury of cranial nerve is sometimes unavoidable, mainly due to the involvement of cranial nerve by tumor, sometimes it can also be caused by excessive stretching during surgery, postoperative edema and scar adhesion, mainly occurring in the sublingual nerve and vagus nerve, but also in the mandibular rim branch of facial nerve and sympathetic nerve, the incidence of which is 19%-78%. Familiarity with the anatomical relationship between the tumor and the adjacent cranial nerves, mastering the details of surgical operation, and maintaining clear exposure of the operative field are important means to avoid or reduce cranial nerve injury. Intraoperative bleeding is an important cause of life-threatening patients during carotid body aneurysm surgery. Blood transfusion should be prepared, and equipment such as autologous blood transfusion and bipolar electrocoagulation should be prepared. In recent years, some scholars have devoted themselves to the study of radiation therapy for carotid body aneurysm. In the past, it was thought that chemoreceptor aneurysms were insensitive to radiation therapy, but with the progress of radiation technology and optimization of radiation protocols, the local control rate of radiation therapy for head and neck chemoreceptor aneurysms has been significantly improved. In conclusion, carotid body aneurysm is an effective means of treatment. In conclusion, carotid body aneurysm is a rare clinical tumor, and early diagnosis and treatment are extremely important to reduce surgical complications and improve the cure rate. The key to early diagnosis is to think of the possibility of carotid body aneurysm for tumors in the anterior carotid area, and imaging should be done for patients suspected of carotid body aneurysm to clarify the diagnosis. Surgery for carotid body aneurysm should be performed by a surgeon with specialized vascular surgery skills.