giovedì 5 aprile 2007

Carotid body (paraganglioma) tumor


Figure 1: Axial contrast enhanced CT image of the upper neck shows a large enhancing mass in relation to the carotid space and is displacing and compressing the vessels.
Figure 2: MRI image of the upper neck shows a large enhancing mass in relation to the carotid space and is displacing and compressing the vessels. Note the multiple small flow voids within the lesion on MRI giving the "salt & pepper" appearance.

Diagnosis: Carotid body (paraganglioma) tumor

Carotid body tumor is a rare type of head and neck tumor composed of paraganglionic cells. Paraganglionic tissue can be found in the adrenal medulla and in multiple extra-adrenal sites, including at the carotid bifurcation, the aortic arch, adjacent to the jugular vein, the tympanic nerve, the facial nerve, the vagus nerve, and others. This tissue develops embryologically from neural crest tissue. These tumors are called extra-adrenal paragangliomas and sometimes as glomus tumors or chemodectomas. The function of paraganglionic tissue in the carotid body is to function as a chemoreceptor, sensing oxygen levels as well as carbon dioxide and pH levels. In head and neck, the glomus tumors are seen at the carotid bifurcation (carotid body tumor) as seen in this case, at the jugular fossa (glomus jugulare), in the middle ear (glomus tympanicum) or along the vagus nerve (glomus vagale).

Carotid body tumors are well encapsulated and highly vascular benign tumors and can occur in a wide range of ages, from childhood to the elderly, but the average age at diagnosis is around 45. There is a slight female predominance, and people who live at high altitudes are more likely to develop carotid body tumors (thought to be due to lower oxygen levels).Most cases are sporadic but familial inheritance is also described. In addition, familial syndromes such as multiple endocrine neoplasia (MEN) can contribute to the development of multiple carotid body tumors as well as tumors at multiple other paraganglionic sites in the head and neck and in the rest of the body as well. Carotid bifurcation is the second most common site for glomus tumors in head and neck, after the middle ear(glomus tymapnicum).

Carotid body tumors like all other paragangliomas are slow-growing and may be locally invasive. They can present as a lateral cervical mass which may or may not be pulsatile. These tumors can sometimes cause cranial nerve palsies, most commonly vagal nerve palsy, and if large can even erode through the skull base or other bony structures. They are rarely malignant in that they rarely metastasize, although local recurrence is not uncommon. 10% of head and neck paragangliomas are multicentric and bilaterality is most common with carotid body tumors. Synchronous and/or metachronous tumors can develop at the contralateral carotid bifurcation as well as in other paraganglionic sites, especially if a familial syndrome is present. These types of recurrences are not usually considered metastases by most sources. Carotid body tumors and other paragangliomas can actively secrete metanephrines, most commonly norepinephrine, although this is rare (3-5% of head and neck paragangliomas). Symptoms of an actively secreting carotid body tumor would include headaches, flushing, hypertension, and palpitations.

CT of the neck is helpful for diagnosis and can identify any local lymph node enlargement or bony erosions. Additionally, MR can help determine the relationship of the tumor with respect to the carotid vessels and other neck structures and if there are multiple paragangliomas present. A classic finding of the carotid body tumor is splaying of the internal and external carotid arteries. On both enhanced CT and MR, the carotid body tumors and other paragangliomas are intensely enhancing due to their extensive vascularity. Sometimes small flow voids can be seen on nonenhanced MR, causing a “speckled” or “salt and pepper” appearance of the tumor. On dynamic enhanced CT or MR, there will be a rapid enhancement, a high peak, and rapid washout due to early arteriovenous shunting of the tumor. Conventional catheter angiography reveals similar findings. In addition, embolization of the tumor can be undertaken during the angiographic exam to reduce blood loss from this highly vascular tumor during surgery. Another study that can be performed to evaluate the carotid body tumor is an Indium-111 octreotide isotope scan which is preferentially taken up by neuroendocrine tissues and can help detect presence of multiple paragangliomas.

Surgical excision is the preferred treatment of head and neck paragangliomas in most cases although it is not without risk. The main risks of excision are injury to local cranial nerves or to the carotid artery and blood loss from these highly vascular tumors. If the tumor is found to encase the carotid extensively, then temporary balloon occlusion of the common carotid artery with EEG monitoring can help determine the adequacy of collateral circulation. If the patient is not a surgical candidate, due to extensive tumor involvement or coexisting morbidities, radiation therapy is an option, although it is considered second-line therapy.

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