The carotid body (CB), described for the first time by Albrecht Von Haller in 1743 [1] is a small structure 12 mg in weight [2] located in the adventitia of carotid bifurcation serving as a chemoreceptor [2] . It has both ectodermic and mesoderm tissue elements and consists of 2 types of glomus cells: type I (chief or paraganglion cells) and type II (sustantecular cells). The CB receives its blood supply mainly from the external carotid artery (ECA) and has afferent innervations via the glossopharyngeal nerve [2] . A rare highly vascular mostly benign tumour may arise from the CB paraganglia previously known as chemodectoma or CB paraganglioma [3] . As the paraganglia are widely distributed in the body (in association with the sympathetic and parasympathetic chains from the skull base to pelvic floor); paragangliomas may arise in different locations such as the abdomen, retroperitoneum, mediastinum, head and neck and best named by their location [4] . Carotid body tumour is the commonest head and neck paraganglioma [1] . The exact etiology of CBT is unknown, although its higher incidence among people living at high altitudes or those with chronic obstructive pulmonary disease suggests a role of chronic hypoxia. The tumour mostly occurs in sporadic form while minority of patients had a familial type which is thought to be related to genetic factors. The tumour is usually non-functional but occasionally tumours capable of catecholamine secretion are diagnosed with symptoms similar to pheochromocytoma such as hypertension and tachycardia [1] [3] . Carotid arteriography used to be the gold standard for diagnosis [5] , although Duplex US scanning and magnetic resonance arteriography (MRA) are favored by many authors nowadays [6] . Carotid BT has a characteristic histopathological appearance [1] -[3] . It represents a surgical challenge due to its location, high vascularity and potential morbidity and mortality [1] [4] [5] . Surgery is the standard therapy as it provides an immediate and complete removal of the tumour [1] [7] -[9] . However, the morbidity of cranial nerve injuries and stroke associated with surgery is significant [10] . On the other hand, the indolent and very slow growth rate of CBT and the fact that most of them are benign and rarely cause death by themselves encourage some authors to adapt the conservative or the so-called (wait and scan) policy [9] . A third group of workers recommend radiotherapy as a primary mode of management of CBTs to achieve a tumour growth control while avoiding the potential morbidity of surgical intervention [9] .

In Iraq, little has been published about this uncommon disease; one paper [7] , one PhD thesis [11] and 2 videos [12] [13] posted on the net demonstrating surgical removal of 2 such tumours. In 2008, Hussen, W. M. [7] described 8 patients in 12-year period (1994-2005) and this is his second case series from the same institute. We aim to present our current management of this uncommon yet serious disease in view of the relevant literature.

Patients with CBTs that were operated upon in the Department of Thoracic and Vascular Surgery, Baghdad Medical City Teaching Hospital over a 4-year period (2010-2014) were enrolled in this prospective study. Detailed history taking and thorough physical examination particularly of the region of the neck were performed. Any cranial nerve involvement was recorded when present. Relevant investigations were ordered such as Duplex US scanning, MRI, MRA, and carotid arteriography (conventional or CT angiography). Preoperative preparation included a thorough medical checkup, fitness for general anaesthesia, blood preparation and written high risk consent was signed by each patient after explaining the possible morbidity and mortality. Due to the non- availability of indwelling Javid carotid shunt, an alternative shunt (Scribner’s shunt of hemodialysis) was pre- pared.

“The patient is positioned supine with the neck rotated to the opposite side. Since the need for carotid resection cannot always be predicted, one leg is prepared in case the saphenous vein should be required. The carotid artery is exposed through a standard anterolateral cervical incision along the anterior border of the sternocleidomastoid muscle. Control of the common, internal and external carotid arteries is obtained and hypoglossal and vagus nerves are identified. Using the bipolar diathermy, a capsular-adventitial or sub-adventitial (white line) dissection plane is established at the inferior margin of the tumour at bifurcation and extended cephalad onto the internal and external carotid arteries. Branches of external carotid artery may require division to facilitate the dissection (Figure 1). This technique is usually adequate for excision of Shamblin Class I and II tumours” [1] (Figures 2(a)-(c)). “Shamblin Class III tumours are often managed by resection of the involved portion of the

artery and replacement with a saphenous interposition vein graft” [1] . Postoperatively, the patients were evaluated with regard to any evidences of cranial nerve injury. If the postoperative period was uneventful, the patients were discharged home once the condition of the patient was stable. Late outcome was assessed through frequent follow-up visits to the consultation clinic. Statistical analysis was performed using z-test for 2 population proportions and T-test for 2 dependent means.

Seven patients (5 males and 2 females). The male to female ratio was 2.5:1. The youngest was a girl of 17 and the oldest was a man of 46. The mean age was 32.9 ± 9.8 year.

Table 1 showed the age and sex distribution. The peak was in the 4^th decade (n = 4, 57.1%).

The patients lived in the middle and south of Iraq except one patient from Kirkuk in the north. The 2 ladies were a housewife and a student whereas men were (workers n = 3, soldier n = 1 and a civil servant n = 1). The demographic and clinical features are shown in Table 2.

There were 5 males and 2 females. All patients had slowly growing painless pulsatile swelling below the angle of the mandible present for long durations (1 to 25 years) and a positive Fontaine̓ s sign. All tumours were unilateral (4 on the right side and 3 on the left side). There was one patient with hypertension, one with palpable cervical lymph nodes and one with prior history of incisional biopsy (Figure 3) but none had a family history of CBT. Ultrasound neck examination with Doppler of carotid arteries was done in all patients. Carotid angiography was done in 5 patients (Conventional carotid angiography n = 2 and CT angiography n = 3). Contrast-en- hanced CT scan of the neck was done twice. All tumours were benign ranging in size from 3 × 3 cm to 6.4 × 3.2 cm. According to Shamblin classification, the majority was in class II (n = 4) followed by class I (n = 2) and one in class III. In all cases, the tumours were successfully resected with preservation of ICA. However, the ECA was ligated twice without bad sequels (in both cases, the ECA was severely involved by the tumour; therefore it was ligated and the tumours were completely excised. The tumours were class II and III and the largest in the series). Lymph nodes were removed in 2 cases and were not malignant. Malignancy was excluded on the basis of absence of regional lymph node involvement and distant metastases. The only postoperative neurological deficit was an ipsilateral tongue deviation that persisted for 1 year in a lady of 35 with Shamblin class II right- sided tumour. No patient died and none has developed a postoperative stroke or recurrence of the tumour during the follow-up period. Table 3 clearly shows that Shamblin class III significantly influenced the occurrence of early neurological deficits (p ˂ 0.05).

^*Slowly growing painless pulsatile swelling below the angle of the mandible for some duration; ^#A swelling moveable horizontally but not vertically; ^@Cervical lymphadenopathy; ^!Hypertension; ^{^}Postoperative neurological deficits; ^$Ipsilateral tongue deviation.

Details of workup are shown in Table 4. The characteristic finding of CBT on US examination is a hypervascular mass at carotid bifurcation with splaying of carotid arteries whereas the conventional and CT angiography usually revealed a tumour blush, splaying of carotid arteries and the feeding vessels of the tumours.

Head and neck paragangliomas are rare neoplasms comprising about 0.03% of all human tumors. The annual incidence is around 0.001% [4] . This study involved 7 patients over a 4-year period (1.75 patients per year). Our first series [7] involved 8 patients in 12 years (0.66 patients per year). (There is a significant rise in hospital- based incidence of CBTs in Iraq since 2008 p ˂ 0.05). Comparing our incidence to others (Table 5); we’ll see that the Mayo Clinic has reported the largest series to-date, describing 153 cases over a period of 50 years (around 3 patients per year) [14] . Most other studies (apart from the Iranian study) reported lower hospital-based inci- dences of CBT (0.7 - 1.3 patient per year). Thus the number of CBTs described in our study is good. The high incidence reported by Salehian et al. from Iran is firstly due to inclusion of pathological lesions other than carotid paragangliomas such as schwannoma and mesenchymoma (when excluded, the incidence would fall to 5.3 patients per year) and secondly due to the high altitude of Tehran (1200 meter above the sea level) which may be an etiological factor for CBTs [7] [8] .

The peak age of the patients was in the 4^th decade. This finding is similar to other reports “Most patients become symptomatic between their 30^th and 60^th birthday” [4] [5] .

In this study, male to female ratio was 2.5:1. However, other studies state that females are more frequently involved [1] [8] [16] . Rodriguez-Cuevas et al. and Luna-Ortiz et al. [cited in 6] declare that male and female distribution is equal except at high altitude where females appear to predominate [6] .

Our study revealed a noticeable increase in the hospital-based incidence of CBT in Iraq since 2008. The diagnosis of CBT can be made easily if a high index of suspicion is coupled with the necessary investigations. Our results of surgery for CBT compare very well with the international standards.

We would like to thank Dr. Sabah N Jaber FIBMS (CTVS) for his permission to report his patient (the 4^th in this series).

None is declared.

A: Study design, B: Data collection, C: Statistical analysis, D: Data interpretation, E: Manuscript preparation, F: Literature search. Waleed M. Hussen: A, B/Abdulsalam Y. Taha: A, B, C, D, E, F/Diar S. Hama-Kareem: A, B.