Carotid body tumours arise from the chemoreceptor cells found at the carotid bifurcation. These are part of a widespread system of such cells which may give rise to tumours known as paragangliomas. Other examples of these are tumours of the vagal body or the glomus jugular and phaeochromocytomas. Patients can present at any age with a carotid body tumour but do so most commonly in the 5th and 6th decades. Although men were originally found to be more often affected, the sex ratio has recently reversed in favour of women.

Carotid body tumours consist of epithelioid ‘chief’ cells arranged in clusters separated by trabeculae of well vascularized fibrous tissue. They have well-defined margins but lack a true capsule. Chemoreceptor cells are, in general, capable of secreting adrenaline and noradrenaline but carotid body tumours are virtually always non-secretory and therefore not associated with symptoms of hypertension. A histological diagnosis of malignancy is based on cellular atypia, mitosis, or local invasion but tends to be unreliable in predicting tumour behaviour. Most behave in a benign fashion; local invasion and lymph node metastases or haematogenous spread, especially to bone, are reported in less than 20 per cent of cases.

There appears to be a genetic susceptibility to these tumours and paragangliomas that arise in families are more likely to be bilateral or multiple. Carotid body tumours appear to be inherited on an autosomal dominant basis. Prolonged residence at high altitude is also associated with an increased incidence of carotid body tumours.

Paragangliomas are rare. Carotid body tumours occur most frequently but even they are uncommon, an incidence of 0.012 per cent of surgical specimens being reported at one hospital. Approximately 10 per cent of these patients have either bilateral or multifocal tumours of the chemoreceptor system. Ten per cent of patients have a genetic basis to their disease and in these the incidence of bilateral/multifocal tumours is approximately 30 per cent.

The most common complaint is of a lump in the neck; this may have been present for a considerable time: one patient was reported to have presented after 47 years! The carotid bifurcation lies close to many important and sensitive structures (Fig. 1) 309 and so expansion of the tumour may lead to cranial nerve paresis (VII, IX, X, XI, and XII) resulting in such symptoms as dysphagia, choking, or hoarseness. Symptoms are reported by approximately 10 per cent of patients.

It is vitally important to appreciate the possibility of a carotid body tumour in a patient who presents with a neck lump in the region of the carotid bifurcation. A misdiagnosis of lymph node enlargement followed by an attempt at excision biopsy can result in excessive blood loss and much embarrassment. Fine needle aspiration in the outpatient department may provide the answer, although this depends on the expertise of the local cytology department. Gray scale ultrasound imaging will confirm the relationship with the carotid bifurcation and should demonstrate splaying of the two branches by the tumour. Duplex scanning is probably more appropriate; it gives more precise identification of the vessels and the extent of their involvement. Angiography is usually performed if duplex or ultrasound examination suggests a carotid body tumour; it demonstrates splaying of the carotid bifurcation, a tumour blush, and often allows tumour feeding vessels to be identified (Fig. 2) 310. In the future colour coded duplex scanning may be able to replace angiography by demonstrating not only the distortion of the carotid bifurcation but also the tumour vascularity. However, confident identification of major feeding vessels for embolization of large tumours (see below) will still require angiography. Enhanced CT images are also helpful in determining the upper level of a large tumour.

If tumours are benign, their natural course is of slow enlargement with eventual compression of local structures resulting in symptoms such as nerve palsies. In the elderly patient without symptoms it may be appropriate to do nothing. However, it is much easier and safer to remove the tumour before extensive local invasion and so in most patients a surgical approach when the tumour is small is advocated. Untreated, 75 per cent asymptomatic patients eventually develop symptoms and 30 per cent will die from invasion of local structures or metastatic disease.

Most patients in whom a diagnosis of carotid body tumour is made should undergo surgical excision.

These tumours are very vascular and if large, excision can result in excessive blood loss. In dealing with tumours greater than 3 cm in diameter it may be an advantage to shrink them preoperatively by embolization. It is essential that an experienced radiologist performs this manoeuvre. There are communications between the main feeding vessels of the tumour from the external carotid artery and the vertebral artery; embolization via the external carotid artery may result in brain embolization. Once the tumour has been successfully devascularized it is important that surgery is performed within the next 2 or 3 days or neovascularization occurs and the advantage is lost.

This is most important to assess cranial nerve involvement but is also useful to look for invasion of the pharynx by upward extension of the tumour, a rare occurrence.

Either investigation is used to assess the extent of upward extension of the tumour and to determine any invasion of the skull base. Magnetic resonance imaging, especially with gadolinium enhancement, may provide some advantages over CT scanning: soft tissue contrast is probably better, an advantage when assessing the extent of invasion by a large tumour, and greater sensitivity allows detection of tumours down to 5 mm in diameter.

There may be extensive blood loss during the surgery because of the vascular nature of the tumour and it is important that at least 4 units of blood are cross matched.

General anaesthesia should be used and nasal rather than oral intubation may be helpful to improve access to a tumour extending up under the mandible towards the base of the skull. Central venous pressure monitoring is mandatory and an arterial line is useful in view of the possibility of excessive blood loss.

Experience with carotid artery surgery is important. It may be necessary to clamp the internal carotid artery, insert a shunt, and even to replace the artery with a length of saphenous vein. If the tumour is known to extend high in the neck the assistance of a craniofacial surgeon is often helpful.

The side of the neck and lower jaw are prepared and draped. The groin should also be prepared in case a length of saphenous vein is required. An incision is made on the anterior border of sternomastoid and dissection extended deeply until the carotid arteries are exposed in their sheath. The common, internal, and external carotid arteries are each exposed and controlled beyond the tumour. Some surgeons advocate dividing the external carotid artery near its origin as soon as possible to reduce vascularity of the tumour and improve access (Fig. 3) 311. Most would advocate at least clamping the artery at this point, although it is not often readily accessible. Heparin is not required prior to this manoeuvre.

The Connell technique in which a straight shunt is inserted via the common carotid artery into the internal carotid artery is another useful approach in that it excludes the external carotid artery from the circulation, thus effectively devascularizing the tumour. A straight Pruitt shunt is ideal for this purpose.

The tumour is dissected out along the white line which demarcates it from the adventitial tissue of the vessels. This dissection should start in the bifurcation and the tumour should be rolled upwards to get a clear view of the cranial nerves which run across the deep aspect of the upper part of the tumour. Good visualization is essential and haemostasis must be performed meticulously so that cranial nerves can be identified and preserved. However greatly they are involved it is usually possible to ‘shell’ the tumour off them. The only exception is the tumour diagnosed as a carotid body tumour which proves to be a vagal body tumour. This arises very close to the carotid bifurcation and can be easily mistaken for the former. The vagus nerve itself is involved and therefore has to be sacrificed. If a carotid body tumour extends well up in the neck, fracture of the styloid process will improve access. It may be necessary to dislocate forward the temporomandibular joint to gain access to its upper border. This is where preoperative CT scanning or MRI and peroperative assistance of a craniofacial surgeon become invaluable.

The Shamblin classification of carotid body tumours groups them according to the degree of invasion of the arterial wall. Those in Group 1 are easy to remove from the vessels, those in Group 2 require dissection in a subadventitial plane to remove them from the vessel, and in those in Group 3, the tumour encircles and invades the vessel to such an extent that it usually requires complete arterial excision and replacement, with a length of saphenous vein. A shunt may be used but it is often useful to have some means of cerebral monitoring such as ECG or transcranial Doppler to monitor distal flow during the procedure. Approximately 50 per cent of carotid body tumours are in Shamblin Group 2 and 25 per cent in each of the other two groups.

Once the tumour is removed and adequate haemostasis achieved the wound should be closed over a vacuum drain which is left in for about 24 h or until significant discharge has ceased.

The patient should be closely monitored postoperatively for central and peripheral neurological deficits (especially of cranial nerves IX, X, and XII, cervical sympathetic nerves, and the marginal mandibular branch of VII) and blood pressure well controlled, particularly if the internal carotid artery has been reconstructed. The incidence of cranial nerve defects associated with surgery has not declined over the years despite improvement in surgical technique (e.g. preoperative embolization to reduce bleeding preoperatively). Such problems are found particularly after removal of large tumours and are reported in 10 to 20 per cent of cases although most recover within a few weeks. Bilateral carotid body tumours should not be removed in the same operation. The incidence of nerve damage following surgery is sufficiently high to make bilateral recurrent laryngeal and hypoglossal nerve palsies a significant risk factor leading to respiratory and swallowing problems postoperatively. In patients who have had surgery to a previous carotid body tumour, resulting in cranial nerve palsy or carotid occlusion, the risks of operation on a contralateral tumour are considerable and radiotherapy (see below) may be preferable. Cerebrovascular accidents occur in less than 3 per cent of cases in most series.

Although the mortality of carotid body tumour removal used to be high (in 1950 it was reported at about 30 per cent) it now should be virtually zero because of innovations such as preoperative embolization, external carotid artery clamping, and well planned strategies for access high in the neck.

Radiotherapy has been promoted by some groups as a primary treatment. Few studies have compared this with surgery and none of these has been a randomized study. Most centres still recommend surgery, with radiotherapy used only for tumours too extensive to excise or as a backup treatment of those with recurrence. Radiotherapy as a primary treatment appears to slow progression of the disease but this is difficult to prove in a disease which naturally has a slow progression rate.

Most patients are cured by surgery and any cranial nerve palsies associated with the procedure are usually temporary although those caused by prolonged compression from the tumour itself are sometimes permanent. A few patients prove to have a malignant tumour, which may be diagnosed histologically, but this usually only comes to light when metastatic disease develops. If the tumour is known to be malignant because of local invasion or metastatic disease, local radiotherapy can be used to prevent local recurrence or to treat metastatic disease as it occurs. Most tumours are slow growing and survival for many years is possible even with established metastatic disease.

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