Prevalence, characteristics, evaluation, and management of carotid body tumors: Systematic analysis based on available evidence.

OBJECTIVE: Although carotid body tumors (CBTs) are rare, they attract particular attention because of their propensity for malignant transformation and the high surgical risk. Because data are scarce and as it is difficult to achieve a large sample size, no study has yet comprehensively analyzed the characteristics, management, or operative complications of CBTs. Therefore, we collected and analyzed all currently available information on CBTs and used the pooled data to derive quantitative information on disease characteristics and management. METHODS: We systematically searched PubMed, Embase, the Cochrane Library, and the Web of Science up to December 1, 2022, for studies that investigated the characteristics and management of CBTs. The primary objective was to identify the prevalence of the various characteristics and the incidence of complications. The secondary objective was to compare patients who underwent preoperative embolization (PE) and those who did not (non-PE), as well as to compare patients with different Shamblin grades and those with and without succinate dehydrogenase (SDH) mutations in terms of CBT characteristics and complications. Two reviewers selected studies for inclusion and independently extracted data. All statistical analyses were performed using the standard statistical procedures of Review Manager 5.2 and Stata 12.0. RESULTS: A total of 155 studies with 9291 patients and 9862 tumors were identified. The pooled results indicated that the median age of patients with CBT was 45.72 years, and 65% were female. The proportion of patients with bilateral lesions was 13%. In addition, 16% of patients had relevant family histories, and the proportion of those with SDH gene mutations was 36%. Sixteen percent of patients experienced multiple paragangliomas, and 12% of CBTs had catecholamine function. The incidence of cranial nerve injury (CNI) was 27%, and 14% of patients suffered from permanent CNI. The incidence rates of operative mortality and stroke were both 1%, and 4% of patients developed transient ischemic attacks. Of all CBTs, 6% were malignant or associated with metastases or recurrences. The most common metastatic locations were the lymph nodes (3%) and bone (3%), followed by the lungs (2%). Compared with non-PE, PE reduced the estimated blood loss (standardized mean difference, -0.95; 95% confidence interval [CI], -1.70 to -0.20) and the operation time (standardized mean difference, -0.56; 95% CI, -1.03 to -0.09), but it increased the incidence of stroke (odds ratio, 2.44; 95% CI, 1.04-5.73). Higher Shamblin grade tumors were associated with more operative complications. Patients who were SDH gene mutation-positive were more likely to have a relevant family history and had more symptoms. CONCLUSIONS: CBT was most common in middle-aged females, and early surgical resection was feasible; there was a low incidence of serious operative complications. Routine PE is not recommended because this may increase the incidence of stroke, although PE somewhat reduced the estimated blood loss and operation time. Higher Shamblin grade tumors increased the incidence of operative complications. Patients who were SDH gene mutation-positive had the most relevant family histories and symptoms.

Non-Functional Carotid Body Tumors in Patients Without Somatic Mutations May Be Considered for Non-Operative Management.

BACKGROUND: Carotid Body Tumors (CBT) are rare neuroendocrine paragangliomas which are typically asymptomatic and benign, with a low rate of biochemical functionality. Historically, early surgical excision was recommended to prevent development of CBT-related complications. Yet, CBT resection can result in significant cranial nerve and vascular injuries. Recent work has shown successful primary observation without resection of non-carotid body, cranial paragangliomas with slow growth and low rate of neuropathies. We hypothesize that primary observation of CBT is safe and may be considered for majority of CBT. METHODS: Retrospective cohort study of patients at a multi-hospital healthcare system with radiologic identification and/or diagnostic or procedural billing codes for CBT (2000-2019). Tumor size (greatest diameter), associated symptoms, and interventions were recorded at the initial evaluation and throughout follow-up. Multivariable logistic regression investigated the risk of initial surgical resection. RESULTS: A total of 108 patients (mean age, 59 ± 19 years; 67% female), with 123 CBT (mean diameter 23 ± 12 mm; 52% right) were initially evaluated by otolaryngologists (51%), vascular surgeons (25%), neurosurgeons (8%), or other (16%) medical providers. Fity-five CBT were initially resected, 63 observed, and 5 irradiated. Initial resection was associated with younger age (adjusted odd ratios aOR, 0.95 [95% confidence intervals CI, 0.92-0.97]), male sex (aOR, 4.82 [95% CI, 1.47-15.75]), and evaluation by a vascular surgeon (aOR, 6.17 [95% CI, 2.04-18.63]). Overall median follow-up was 4.7 (IQR, 2.6-9.1) years. Initially observed CBT were on an average stable in size (mean 1 ± 5 mm/year), none became biochemically active, and 2 patients became symptomatic. At the final follow-up, 63 (51%) underwent surgical resection, 54 (44%) observation, and 6 (5%) radiation therapy. Of the 63 surgically resected CBT, 5 (8%) patients had malignant CBT of which 3 (60%) had known somatic mutations (polymerase epsilon [n = 1], succinate dehydrogenase-D gene [n = 2]). Thirty percent of CBT resections had in-hospital postoperative complications, notably including 1 stroke which occurred in an initially observed patient and 16 cranial nerve complications which all occurred in immediately resected patients. Three resected CBT locally recurred, only 1 of which had malignant pathology. CONCLUSIONS: Patients with newly diagnosed CBT require biochemical functionality and somatic mutation testing. In the absence of these findings, initial observation of CBTs with annual imaging and symptom monitoring may be considered an alternative to immediate resection which demonstrates a high risk of clinically meaningful postoperative complications.

Improving Outcomes in Carotid Body Tumors Treatment: The Impact of a Multidisciplinary Team Approach.

BACKGROUND: The purpose of this study was to evaluate how a multidisciplinary approach, including patients and familiar genetic counseling, preoperative succinate-dehydrogenase (SDH) gene mutation analysis, preoperative adjunctive endovascular procedures (PAEPs) and postoperative rehabilitative team may affect the outcomes in patients who underwent surgery for carotid body tumors (CBTs). METHODS: Fifty-seven consecutive CBT resections were performed from January 1995 to December 2019 in a single center institution. Two groups of patients were compared: group A (1995-2003; n = 10) and group B (2004-2019; n = 47), treated before and after the establishment of a multidisciplinary approach to CBTs. Group A and group B were evaluated retrospectively and prospectively for SDH mutations, respectively. PAEPs (external carotid artery stenting, percutaneous transfemoral embolization or direct percutaneous puncture of the tumor with simultaneous embolization) were performed only in patients of group B, when the size of the tumor exceeded the 45 mm. Primary endpoints were blood loss (BL) and cranial nerve injuries. Secondary endpoint was the number of new silent masses (NSMs) discovered after genetic evaluation. RESULTS: SDH mutations were found in 2 patients of group A and in 11 patients of group B. There were no significant differences in mass diameter between the groups. A significant difference regarding the surgical procedure time was observed in the 2 groups, with a higher time in the group A (Group A: 180 ± 77.3; Group B: 138 ± 54.5, P= 0.04). BL was significantly lower in group B (203 ± 69.5 mL vs. 356 ± 102 mL; P = 0.0001), as well as for patients underwent PAEPs vs. those underwent direct surgery (n = 15, 149 ± 53 mL vs. n = 42, 273 ± 88 mL; P = 0.0001). No differences between transient and persistent cranial nerve injuries were observed between the 2 groups. Carotid reconstruction was necessary for 2 patients of group A (n = 2 vs. n = 0; P = 0.02). Unilateral tumor recurrence was detected in 7 patients, with a significantly higher rate (P ≤ 0.002) in patients carrying SDH mutations compared to those without SDH mutation (wild-type). SDH mutations detected in the groups lead to discover 7 NSMs (group A n = 1 vs. group B n = 6; P = 1.00). CONCLUSION: The impact of the multidisciplinary team suggests that surgical resection still remains the gold standard for the treatment of CBTs, but the use of PAEPs in selected cases may reduce surgical procedure time, BL and the need for reconstructive carotid surgery. Genetic counseling and SDH gene analysis allow to diagnose NSMs in asymptomatic patients. Larger studies should be considered to evaluate the effectiveness of postoperative rehabilitative program.

Immunohistochemistry and Mutation Analysis of SDHx Genes in Carotid Paragangliomas.

Carotid paragangliomas (CPGLs) are rare neuroendocrine tumors often associated with mutations in SDHx genes. The immunohistochemistry of succinate dehydrogenase (SDH) subunits has been considered a useful instrument for the prediction of SDHx mutations in paragangliomas/pheochromocytomas. We compared the mutation status of SDHx genes with the immunohistochemical (IHC) staining of SDH subunits in CPGLs. To identify pathogenic/likely pathogenic variants in SDHx genes, exome sequencing data analysis among 42 CPGL patients was performed. IHC staining of SDH subunits was carried out for all CPGLs studied. We encountered SDHx variants in 38% (16/42) of the cases in SDHx genes. IHC showed negative (5/15) or weak diffuse (10/15) SDHB staining in most tumors with variants in any of SDHx (94%, 15/16). In SDHA-mutated CPGL, SDHA expression was completely absent and weak diffuse SDHB staining was detected. Positive immunoreactivity for all SDH subunits was found in one case with a variant in SDHD. Notably, CPGL samples without variants in SDHx also demonstrated negative (2/11) or weak diffuse (9/11) SDHB staining (42%, 11/26). Obtained results indicate that SDH immunohistochemistry does not fully reflect the presence of mutations in the genes; diagnostic effectiveness of this method was 71%. However, given the high sensitivity of SDHB immunohistochemistry, it could be used for initial identifications of patients potentially carrying SDHx mutations for recommendation of genetic testing.

Current surgical management of carotid body tumors.

BACKGROUND: Carotid body tumors (CBTs) are rare. Management guidelines may include genetic testing for succinate dehydrogenase (SDH) mutations. We performed an institutional review of the surgical management of CBT. METHODS: A retrospective analysis (1994-2015) of CBT excisions at our institution was performed. Data obtained included demographics, genetic testing (if performed), intraoperative details, postoperative morbidity, and long-term outcomes. Data from the first CBT excision were included in patients with bilateral tumors. Genetic testing was routinely offered in patients with a family history of CBT or multiple paragangliomas. RESULTS: A total of 183 CBTs (124 female [67.7%]) were excised. A neck mass was present in 106 patients (57.9%), 24 patients (12.1%) presented with tenderness or neck pain, and 3 (1.6%) presented with cranial nerve dysfunction. Computed tomography (57.9%) or magnetic resonance imaging (51.3%) were the most commonly used imaging modalities. Preoperative angiography was performed in 73 patients (39.8%), and 62 of them (84.5%) underwent embolization or internal carotid balloon occlusion testing, or both. Mean tumor diameter was 3.2 cm (range, 0.6-7.2 cm). There were 71 (38.8%), 75 (41%), and 37 (20.2%) Shamblin type 1, 2, and 3 tumors, respectively. Average operating time was 224 minutes (range, 52-696 minutes). Average blood loss was 143.9 mL (range, 10-2000 mL). Arterial reconstruction with an interposition graft was required in 10, and patch angioplasty was performed in four. Cranial nerve injury was permanent in 10 (5.5%), and the rate of stroke was 1% (n = 2). A total of 382 lymph nodes were excised, and all were benign. There were no deaths ≤30 days. Only one patient presented with malignant disease 2 years after CBT excision, and this patient did not undergo genetic testing. Thirty-four (18.6%) had a family history of CBT. SDH testing was performed in 18 patients, and 17 tested positive. Positive genetic testing had a correlation with earlier age at operation (P < .0001). Mean age at diagnosis of patients with SDH mutations was 38.0 years, and patients without known SDH mutations presented at a mean age of 50.3 years. In patients with SDH mutations, tumor diameter, operating time, blood loss, and distribution of Shamblin type 1, 2, and 3 lesions were not significantly different compared with the control group. CONCLUSIONS: CBT can be treated with minimal morbidity and mortality; however, the subgroup of patients with positive SDH mutations may represent a variant group of younger patients. Vascular surgeons should be aware of genetic testing to identify patients and family members who should undergo additional preoperative testing and monitoring for other paragangliomas. Concomitant lymph node dissection does not appear to add value in absence of clinic suspicion for malignancy.

The presence of SDHB mutations should modify surgical indications for carotid body paragangliomas.

OBJECTIVE: The aim of this study was to determine whether the genetic background of the disease should be incorporated into treatment decision making. BACKGROUND: Carotid body paragangliomas are rare tumors that often affect patients with genetic mutations of the succinate dehydrogenase complex (SDHx). Despite growing evidence that germ line genetic mutations alter the aggressiveness of paragangliomas, treatment decisions are currently based only on clinical symptoms and tumor size in patients with carotid body paragangliomas. METHODS: Retrospective analysis of 34 patients with carotid body paragangliomas who underwent genetic testing and surgical treatment. Recurrence was defined by the return of locoregional disease and/or development of distant metastases. Clinical characteristics and genetic testing results were analyzed as predictors of patient outcomes. RESULTS: Thirty-four patients underwent 41 primary carotid body paraganglioma resections (median follow-up time of 42 months, range: 1-293). Overall survival was 91.2%. Twelve patients had germ line mutations in SDHB, 17 in SDHD, and 5 carried no known mutation. Surgical resection of larger tumors was associated with higher operative complications (odds ratio: 5.4, P = 0.05). Tumor size at resection was significantly smaller in patients with SDHB mutations than in patients with non-SDHB mutations (2.1 vs 3.3 cm, P = 0.02). Patients with a mutation in the SDHB gene also had significantly worse disease-free survival compared with patients without an SDHB gene mutation (P = 0.03). CONCLUSIONS: Mutations in the SDHB gene are associated with worse disease-free survival after resection in patients with carotid body paragangliomas despite earlier intervention. This suggests that a more aggressive surgical approach is warranted in patients with SDHB mutations.

SDHB gene mutation in a carotid body paraganglioma: case report and review of the paraganglioma syndromes.

Carotid body tumors represent the most common of head and neck tumors. They account for <0.03% of all human tumors. The underlying physiology and pathogenesis of this tumor type are not well understood. Several different genetic abnormalities have been associated with the development of carotid body paragangliomas. We present a case report with an unusual genetic mutation in the SDHB gene and a review of the paraganglioma syndromes.

Malignant carotid body tumors: What we know, what we do, and what we need to achieve. A systematic review of the literature.

Malignant carotid body tumors (MCBT) are rare and diagnosed after detection of nodal or distant metastases. This systematic review (SR) focuses on MCBT initially approached by surgery. Preferred Reporting Items for SR and Meta-Analysis (MA) guided the articles search from 2000 to 2023 on PubMed, Scopus, and Web of Science. Among 3548 papers, 132 (337 patients) were considered for SR; of these, 20 (158 patients) for MA. Malignancy rate was 7.3%, succinate dehydrogenase (SDH) mutation 17%, age at diagnosis between 4th and 6th decades, with a higher prevalence of females. MCBTs were mostly Shamblin III, with nodal and distant metastasis in 79.7% and 44.7%, respectively. Malignancy should be suspected if CBT >4 cm, Shamblin III, painful or otherwise symptomatic, at the extremes of age, bilateral, with multifocal disease, and SDHx mutations. Levels II-III clearance should be performed to exclude nodal metastases and adjuvant treatments considered on a case-by-case basis.

Current management of carotid body tumors.

Carotid body tumors (CBTs) are neoplasms that occur at the bifurcation of the carotid artery and are pathologically classified as paragangliomas. In the 4th edition of the WHO classification, paragangliomas are categorized as neoplasms with malignant potential. Clinically, about 5% of CBTs present with malignant features such as metastasis. Currently, it is challenging to distinguish between tumors with benign courses and those that present malignantly. Recent advances in genetic testing have elucidated the genetic characteristics of paragangliomas, including carotid body tumors. Over 20 genes have been identified as being involved in tumor development. Particularly in head and neck paragangliomas, abnormalities in genes related to succinate dehydrogenase are frequently observed. Research is ongoing to understand the mechanisms by which these genes contribute to tumor development. The definitive treatment for CBTs is surgical resection. These tumors are prone to bleeding and often adhere firmly to the carotid artery, making intraoperative bleeding control challenging. The risk of lower cranial nerve paralysis is relatively high, and there is a risk of stroke because of manipulation of the carotid artery. Preoperative evaluation with angiography is essential, and a multi-disciplinary surgical team approach is necessary. In cases where the tumor is difficult to resect or has metastasized, radiation therapy or chemotherapy are employed. Clinical trials involving targeted molecular therapies and radiopharmaceuticals have recently been conducted, with some applied clinically. The development of various new treatments is anticipated, providing hope for therapeutic options in refractory cases.

[Endothelial cells and fibroblasts mediate the microenvironmental regulatory network of carotid body paraganglioma].

Objective:To explore the gene expression characteristics of endothelial cells and fibroblasts in the microenvironment of SDHD-mutated carotid body tumors（SDHD-CBT）, to fine the functional enrichment of each subcluster, and to further explore the network of cell-cell interactions in the microenvironment of SDHD-CBT. Methods:The bioinformatics analysis was used to download and reanalyze the single-nuclear RNA sequencing data of SDHD-CBT, SDHB mutated thoracic and abdominal paraganglioma（SDHB-ATPGL）, SDHB-CBT, and normal adrenal medulla（NAM）, to clarify the information of cell populations of the samples. We focused on exploring the gene expression profiles of endothelial cells and fibroblasts subclusters, and performed functional enrichment analysis based on Gene Ontology（GO） resources. CellChat was used to compare the cell-cell interactions networks of different clinical samples and predict significant signaling pathways in SDHD-CBT. Results:A total of 7 cell populations were profiled. The main subtypes of endothelial cells in SDHD-CBT are arterial and venous endothelial cells, and the main subtypes of fibroblasts are myofibroblasts and pericytes. Compared to NAM, SDHB-CBT and SDHB-ATPGL, cell communication involving endothelial cells and fibroblasts in SDHD-CBT is more abundant, with significant enrichment in pathways such as FGF, PTN, WNT, PROS, PERIOSTIN, and TGFb. Conclusion:Endothelial cells and fibroblasts in SDHD-CBT are heterogeneous and involved in important cellular interactionprocesses, in which the discovery of FGF，PTN，WNT，PROS，PERIOSTIN and TGFb signals may play an important role in the regulation of microenvironment of SDHD-CBT.

Paraganglioma of the carotid body: treatment strategy and SDH-gene mutations.

OBJECTIVES: The aim of the present study was to review treatment results in patients with paraganglioma (PGL) of the neck presenting as carotid body tumour, long-term follow-up and relevance of genetic testing for succinate dehydrogenase (SDH)-gene mutations. DESIGN: Retrospective analysis of prospectively collected data and prospective genetic analysis. MATERIALS AND METHODS: Over a 25-year period (1987-2011) 50 patients were operated for 63 PGLs of the neck. Pre-, intra- and postoperative findings were analysed. Sanger sequencing was performed for genetic testing of SDH-gene mutations (SDH B, SDHC and SDHD). RESULTS: Fifty patients underwent resection of 63 PGLs (62 benign, one malignant) without mortality. Eight patients underwent preoperative embolisation. Vascular surgical procedures were required in 15 operations (15/63 = 23.8%). Nerve lesions occurred after 13 operations (13/63 = 20.6%) and were associated with large tumours. A total of 44 patients are alive after a mean follow-up of 9.8 years. In 40 patients 17 SDH-gene mutations were detected (17/40 = 42.5%): 14 SDHD mutations, two SDHB mutations and one rare SDHC mutation. CONCLUSION: Surgery for PGL is recommended. All PGL patients should be screened for SDH mutations because it impacts the individual follow-up strategy. Whereas all PGL patients require annual ultrasound control, mutation carriers and family members with proven mutations should in addition be regularly examined by magnetic resonance imaging (MRI) of head, neck, thorax, abdomen and pelvis.

SDH deficiency is very common in carotid body paragangliomas: Genetic counseling and testing should be offered to all patients.

BACKGROUND: Collectively, germline pathogenic variants in succinate dehydrogenase (SDH) genes are the most common cause of hereditary paragangliomas. Loss of immunohistochemical expression of SDHB protein (termed SDH deficiency) occurs whenever there is biallelic inactivation of any SDH gene. We sought to estimate the prevalence of SDH deficiency in patients with carotid body paragangliomas. METHODS: We identified all carotid body paragangliomas that had undergone surgical excision at our institution over the last 30 years. If SDHB immunohistochemistry was not performed at the time of excision, it was performed on archived material. RESULTS: There were 64 carotid body paragangliomas identified in the 62 patients. Two-thirds of the patients were female, and 43 (67%) were SDH-deficient. CONCLUSION: Up to two-thirds of all carotid body paragangliomas are associated with SDH deficiency. Therefore, genetic testing and counseling should be offered to all patients with carotid body paragangliomas, regardless of age or family history.

Contiguous bilateral head and neck paragangliomas in a carrier of the SDHB germline mutation.

Paragangliomas are extremely rare neoplasms with multicentric presentation usually linked to familial tumor syndromes. This patient presented with the uncommon combination of concurrent bilateral carotid body tumors and a unilateral glomus jugulare mass that demonstrated vascular continuity. During treatment, the patient was found to be heterozygous for the SDHB germline mutation, an autosomal dominant genotype of the familial paraganglioma syndromes associated with increased malignancy. The unique profile of the SDHB patient as regards primary evaluation, surgical considerations, and extended surveillance was explored and has led to a proposed treatment algorithm for these patients.

Case of spontaneous regression of carotid body tumor in a SDHD mutant: a discussion on potential mechanisms based on a review of the literature.

BACKGROUND: Head and neck paragangliomas are tumors associated with the parasympathetic nerve system and typically show an indolent growth pattern. Therefore a conservative management strategy is considered in selected cases. METHODS AND RESULTS: We present a case of a female patient who presented in 2003 with bilateral carotid body tumors and a tympanic tumor, associated with a mutation in the succinate dehydrogenase -sub-unit-D (SDHD). She was operated on the right carotid body tumor and the tympanic tumor. Thereafter the follow-up was performed with MR examinations at 2-year intervals. After an initial stable phase, over the last 3 years a spontaneous near-total regression of the contralateral carotid body tumor was observed, with only subtle rest-abnormalities visible in 2011. CONCLUSIONS: The present case underlines the indolent growth pattern of head and neck paragangliomas and for the first time describes a rare manifestation of spontaneous regression of a carotid body tumor. The literature was reviewed to discuss this phenomenon.

Bilateral Giant Familial Carotid Body Tumors With Concomitant Skull-Base Paraganglioma and Facial Nerve Palsy.

Carotid body tumors, rare neck paragangliomas arising from the common carotid artery bifurcation, can be classified as sporadic, hyperplastic, or familial. The familial type is often bilateral and associated with germline mutation of the mitochondrial enzyme succinate dehydrogenase. We report the rare case of a 42-year-old man who presented with bilateral giant familial carotid body tumors associated with a concomitant skull-base paraganglioma, left-sided facial nerve palsy, and an incomplete circle of Willis. We describe the excision of the tumors in 2 stages (the left mass and associated paraganglioma first and the right mass second), 6 months apart, with use of general anesthesia, and we discuss other operative considerations.

Synchronous carotid body and thoracic paraganglioma associated with a germline SDHC mutation.

Paraganglionic tumors are rare. A germline mutation responsible for a familial pattern of paragangliomas (PGLs) has been identified on the genes encoding for the subunits of succinate dehydrogenase (SDH). Manifestations of those with a succinate dehydrogenase subunit C (SDHC) germline mutation have been almost exclusively reported as single head and neck paragangliomas (HNPGLs). We present a 32-year-old man with a familial SDHC mutation who manifests synchronous PGLs of the carotid body and the thoracic aortopulmonary window. To our knowledge, this is the first report of such a presentation for this mutation.

A case of carotid body paraganglioma and haemangioblastoma of the spinal cord in a patient with the N131K missense mutation in the VHL gene.

The article describes paraganglioma case in woman with von Hippel-Lindau disease. She was found to be a carrier of a rare germline mutation in the VHL gene (393C>A; N131K). The patient developed large, untypical for von Hippel-Lindau disease, carotid body paraganglioma at the common carotid artery bifurcation. The carotid body paraganglioma coexisted with the haemangioblastoma situated intramedullary in region C5/C6. The haemangioblastoma reached the right-sided dorsal part of the spinal cord in section C5/C6. It produced radicular symptoms within C5/C6, followed by the later paresis of the right limbs. The haemangioblastoma was resected completely. Twelve months after the operation, the spinal symptoms receded and the carotid body paraganglioma still was asymptomatic. The current case of carotid body paraganglioma in patient with the 393C>A (N131K) missense mutation in the VHL gene, supports association of this specific mutation and VHL disease type 2, and suggests its correlation with susceptibility to paragangliomas.

Identification of Isocitrate Dehydrogenase 2 (IDH2) Mutation in Carotid Body Paraganglioma.

Carotid body paragangliomas (PGLs) are rare neuroendocrine tumors that develop within the adventitia of the medial aspect of the carotid bifurcation. Carotid body PGLs comprise about 65% of head and neck paragangliomas, however, their genetic background remains elusive. In the present study, we report one case of carotid body PGL with a somatic mutation in the gene encoding isocitrate dehydrogenase 2 (IDH2). The missense mutation in IDH2 resulted in R172G amino acid substitution, which exhibits neomorphic activity and production of D-2-hydroxyglutarate.