33.1  Commentary

Paragangliomas are usually benign tumors from a collection of anatomically dispersed neuroendocrine organs associated with the autonomic nervous system and characterized by morphologically and cytochemically similar neurosecretory cells derived from the neural crest.1 The paraganglia play an important role in homeostasis, either by acting directly as chemical sensors or indirectly by secreting catecholamines in response to stress. The paragangliomas are generally divided into two groups, those occurring in the head and neck region and those occurring elsewhere, with the adrenal medulla being the most frequent site. The most common locations of paraganglia in the head and neck region are the carotid bifurcation, the vagal nerve, the jugular foramen, and the tympanic space of the middle ear. The carotid body tumors (glomus caroticum), tumors in the carotid bifurcation, are the most common type of head and neck paraganglioma.

The carotid body is a small highly vascularized, ellipsoid structure located in the adventitia of the bifurcation of the common carotid artery.2 The carotid body functions as an oxygen sensor and stimulates the cardiopulmonary system in hypoxia through afferent input by way of the glossopharyngeal nerve to the medullary reticular formation.3 Carotid body tumors can develop spontaneously and can be induced by chronic hypoxia. The latter includes living at high altitudes and certain medical conditions (patients with chronic obstructive pulmonary disease, cyanotic heart diseases).4–6 Familial cases are frequently bilateral or multifocal and have an earlier age of detection.7 The inheritance pattern of paraganglioma is autosomal dominant modified by maternal genomic imprinting.8 Five geneticlocihavebeenidentified.8–12 Themajorityofthetumorsarebenignbutlocalexpansion can cause cranial nerve deficits and invasion of local structures such as the skull base and the parapharyngeal space. Malignancy is observed in about 5% of cases.13 Malignancy cannot be defined on the basis of unique histological criteria of the tumor itself, but only by the presence of metastases, mostly in regional lymph nodes.14

33.2 

Clinical Presentation

Carotid body tumors can be distinguished from other diseases, such as enlarged lymph nodes, aneurysms of the carotid artery, goitre of the right thyroid lobe, and cystic neck lesions by a detailed history and physical examination. Although carotid body tumors can occur at any age, they typically present themselves between the third and sixth decades of life.15 The presence of an asymptomatic palpable mass, slowly growing in the anterior triangle of the neck, must raise suspicion for this diagnosis. In addition to this mass, the patient may present with cranial nerve deficit like hoarseness, tongue paresis, and dysphagia. Hormone production, like catecholamine secretion by the tumor, is generally present in only 5% of patients13 and can cause hypertension.

On physical examination, the pulsatile mass can be moved laterally, but not vertically because of adherence to the carotid artery. A bruit may be heard over the mass, but this is a rare condition. Special attention should be made to the two most damaged cranial nerves in the case of a carotid body tumor: Paresis of the hypoglossal nerve causes tongue dysfunction and paresis of the vagal nerve causes hoarseness. [Q1: B]

A duplex ultrasound is usually performed to differentiate between a carotid body tumor and other possible diseases (Fig. 33.1). For further investigation magnetic resonance imaging(MRI)isthepreferredmethodtovisualizethecircumscriptmassatorabovethecarotid bifurcation (Fig. 33.2). Also, other locations of paraganglioma in the head and neck region can be identified with this imaging technique. [Q2; B, D] Use of contrast material usually showsa“saltandpepper”appearancecausedbyvesselswithsignal-voidswithinthetumor tissue. This shows the marked vascularization of the tumor which may help to differentiate them from other tumors with less vessels. If a paraganglioma is present, at least at one occasion the plasma and urine levels of catecholamines should be checked.

A somatostatine receptor scintigraphy (Fig. 33.4) is a nuclear scan that uses an injected radiolabeled somatostatin analogue octreotide. Somatostatin receptor scintigraphy can be used to detect paragangliomas as they contain somatostatin receptor carrying tissue. The patient receives an intravenous injection of this substance and imaging takes place after 24 and 48 h. Somatostatin receptor scintigraphy has a much higher sensitivity for paraganglioma than a MIBG scan16 [Q2: B, D] If a carotid body tumor is suspected, fine needle aspiration should not be performed and certainly an incision biopsy should be avoided in all cases. The diagnosis of a carotid body tumor is difficult to make on fine needle aspiration and both procedures can give rise to unnecessary complications such as massive bleeding.

33.3  Treatment

Thepreferredtreatmentforcarotidbodytumorsiseitherconservativeorsurgical.Excision is the preferred definitive treatment, although the postoperative morbidity rate as quoted in the literature is rather high. Morbidity includes cranial nerve dysfunction, mostly of nerves X and XII, but also other nerves can be damaged like the glossopharyngeal nerve, the facial nerve or the sympathetic nervous system. [Q3: E] Tumor size is important as larger tumors have a higher incidence of complications.17 Postoperative mortality should not exceed2–5%andoccursonlyinlargetumors,whilemortalityisnegligibleinsmalltumors. Damage to the wall of the carotid artery, especially in the bifurcation, which is difficult to repair because the vessel wall is very thin as a result of dissection in the subadventitial space, may force the surgeon to clamp the internal carotid artery, sometimes leading to ischaemic stroke and death.

In 1972, Shamblin proposed a surgical classification for carotid body tumors based on their tendency to encase the carotid arteries. Shamblin group I are small tumors with minimal attachments to the carotid vessels. Surgical excision can be performed without difficultyandthepercentageofcranialnervedamageisverylow.ShamblingroupIItumorsare

larger and partially encase the carotid arteries, while Shamblin group III tumors are very large tumors that completely encase the carotid arteries. The percentage of cranial nerve damage in Shamblin II tumors is around 7%.17 In Shamblin III tumors, it is sometimes even necessary to sacrifice the carotid bifurcation to be replaced by a venous or synthetic interposition graft in order to reconstruct the carotid artery.18 [Q4: C]

Embolization of the feeding branches of the external carotid artery or other main arteries can be performed a fewdays prior to surgerywith the intention to decreasebloodloss during operation.Although,thisisanareaofcontinuingcontroversy,somegroupsclaimthatembolization decreases blood loss during the operation.19–21 Others have not found the embolization procedure helpful and they warn of the increased risk of stroke caused by emboli to the brainthroughcollateralpathways.22,23 Embolizationhasalsobeenusedinthepastasanalternative treatment option in very high-risk patients who probably would not tolerate surgical excision.24 In our patient, 1 year after the embolization procedure the tumor was still shrinkinginsizeandwestillhavenotoperatedthispatientandresectedthecarotidbodytumor.The risk of waiting even longer is the ability of these tumors to recruit new vessels so that perfusion and size will increase after a while. We are very hesitant to believe that embolization alone will be a definitive solution for these kind of tumors. [Q5: 5]

Radiation therapy is infrequently used as a treatment option for carotid body tumors. Radiotherapy is, however, a good alternative to surgery, especially for large, fast growing tumors, which are not eligible for surgery. Radiotherapy is effective in arresting growth, but it normally does not result in complete eradication of the tumor.25 There is no evidence showing that chemotherapy might be effective against carotid body tumors.

33.4  Summary

Paragangliomas are slowly growing, benign tumors. The carotid body tumor is the most common type in the head and neck region. The diagnosis is suspected from the patient’s history and physical examination. Ultrasound and MRI can usually confirm the diagnosis, while a somatostatin receptor scintigraphy is a reliable method for detecting multiple tumors and tumors at others locations. If the carotid body tumor is small and there is no documented growth, a wait-and-see policy is justified. A fast growing or large tumor should be treated surgically, cranial nerve dysfunction being the most common postoperative complication.

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