Imaging of Head and Neck Glomus Tumors 

Preferred examination

Imaging is the primary investigative modality for glomus tumors of the head and neck. A combination of contrast-enhanced computed tomography (CT) scanning, magnetic resonance imaging (MRI), and angiography is ideal for proper diagnosis and localization of the tumors. Lesions show a characteristic signature on the images, which is based on its location.

Glomus tumors are displayed in the images below.

Currently, MRI is frequently the imaging study of choice for primary diagnosis, followed by contrast-enhanced CT imaging. Angiography remains of paramount importance if the diagnosis is obscure or if embolization is contemplated.^{[18, 19, 20]}

Glomus tumors represent 0.6% of neoplasms of the head and neck and 0.03% of all neoplasms; they are the most common tumors of the inner ear and the second most common tumors of the temporal bone after schwannomas.

Haller introduced glomus tumors of the head and neck into the medical record in 1762 when he described a mass at the carotid bifurcation that had a glomus body–like structure. In 1950, Mulligan renamed this type of neoplasm as a chemodectoma to reflect its origins from chemoreceptor cells. In 1974, Glenner and Grimley renamed the tumor paraganglioma on the basis of its anatomic and physiologic characteristics. They also created a classification method based on the location, innervation, and microscopic appearance of the tumors.^[1]

Anatomy

Glomus tumors of the head and neck are associated with 4 primary locations, the jugular bulb, middle ear cavity, vagus nerve, and carotid body.

Tumors in the jugular bulb region are commonly called glomus jugulare tumors^{[2, 3, 4, 5, 6, 7]} ; they arise in the adventitia of the dome of the jugular bulb. This is the most common type of glomus tumor of the head and neck.^{[2, 3]}

Tumors in the area of the middle ear cavity are commonly called glomus tympanicum tumors(see the image below)^{[7, 8, 9, 10, 11]} ; they arise from the glomus bodies that run with the tympanic branch of the glossopharyngeal nerve. Although glomus tympanicum tumors are the most common primary neoplasms of the middle ear, these tumors are the rarest of head and neck glomus tumors.^{[8, 12]}

Tumors in region of the vagus nerve are commonly called glomus vagale tumors because of their usual close association with the vagus nerve (see the image below).^{[13, 14, 15]} Specifically, they arise infratemporally along the course of the cervical vagus nerve.

Carotid body glomus tumors, also called carotid body tumors, occur at the bifurcation of the common carotid artery and arise from the tissue of the normal carotid body (see the image below).^{[12, 15, 16, 17]}

Although glomus tumors usually appear as solitary lesions at 1 site, multiple lesions at multiple sites are not uncommon (see the image below). Because they are parts of the neuroendocrine system, these tumors are highly vascularized. Clusters of tumor cells (type I cells interspersed with type II cells), called zellballen, are surrounded by a dense network of capillary caliber blood vessels.

Limitations of techniques

CT imaging is excellent at demonstrating cervical masses along the course of the carotid artery, but findings of skull-base soft-tissue details can be limited. However, CT imaging is superb for demonstrating characteristic bony destructive skull-base changes. CT scanning is also best in the diagnosis of glomus tumors when a satisfactory bolus of contrast material is administered. If peak tumor opacification is missed at CT scanning, the mass can be misconstrued for a nonenhancing schwannoma or nodal lesion.^{[18, 19, 20]}

MRI can demonstrate soft-tissue masses and their relationships to adjacent structures well in multiple imaging planes. This capability is particularly helpful in skull-base imaging, in which both extracranial and intracranial components can be evaluated. MRIs can fail to depict enhancement if the contrast agent bolus is inadequate. MRI is inherently limited in its ability to show subtle areas of bony destruction, which may be important for proper diagnosis.^[20]

Angiography is typically reserved for patients who are undergoing preoperative evaluation or for cases in which the presence of neovascularity can help in focusing the differential diagnosis. Angiography is a minimally invasive test and, therefore, not the imaging study of choice. Rarely, diagnostic angiography can show soft-tissue neovascularity in other types of abnormalities, such as those encountered with hypervascular lymphadenopathy or nodular fasciitis. These tumors can have profound neovascularity that mimics that of glomus tumors.^[19]

Radiologic intervention

Embolization is a common technique used as the lone treatment option or as a precursor to surgical excision. As a result of the highly vascular nature of these neoplasms, embolization is an effective technique that is aimed at starving the lesion of its blood supply and inducing necrosis. This is the primary and, at times, the only treatment option for glomus jugulare tumors because of the difficulty in excising many of the tumors. In combination with surgical excision, embolization is often used to reduce blood loss, and it has been proven to be highly effective.

In bilateral lesions, especially of the vagale type, embolization is often required as the sole course of treatment for 1 of the lesions, in tandem with surgical excision of the other. This approach is used because of the proximity of the lesion to the vagus nerve and the occasionally inevitable perioperative damage to the nerve during excision.

As a result of their inherent neovascularity, catheter-directed embolization is appropriate in the treatment of chemodectomas, particularly if surgical removal is contemplated. The use of microcatheters allows precise delivery of embolic agents into masses and embolization of multiple, small, feeding trunks. Although glomus tumors may arise from multiple arterial territories, embolization is typically limited to the feeders of the external carotid branch artery.

In the author's practice, glomus tumor embolization is performed in a preoperative setting. Nevertheless, some authors suggest that embolization alone may be beneficial in the treatment of these tumors.

Special concerns

Whenever external carotid embolization is performed, care must be taken to avoid inadvertent extracranial-intracranial embolization and the subsequent risk of stroke. Occult occipital-vertebral connections may be present or open, or they may become apparent on angiograms, only after partial embolization is performed.

Because pterygopalatine–internal carotid collaterals, as well as middle meningeal–middle cerebral communications, may exist, these should be recognized before embolization. In addition, the ophthalmic artery should be identified before external carotid embolization, and care should be taken to identify any existing ethmoidal-ophthalmic arterial communications.

Contrast-enhanced CT scans demonstrate enhancing soft-tissue masses at characteristic locations key to the diagnosis. Nonenhanced CT imaging can demonstrate glomus tumors, but the demonstration of a strongly enhancing mass is typical in the diagnosis of a glomus tumor.^{[11, 18]}

CT scanning demonstrates carotid body tumors at the level of the carotid bifurcation, respectively splaying the internal and external carotid arteries medially and laterally. These tumors can vary in size, but their location within the bifurcation is critical for diagnosis (see the image below).

Glomus vagale tumors are masses with similarly strong enhancement. These tumors are seen along the course of the jugular vein and internal carotid artery above the level of the carotid bifurcation but below the skull base. These tumors can vary in size, and they can displace adjacent vascular structures (see the image below).

Glomus jugulare tumors are enhancing soft-tissue masses at the skull base, but skull-base artifact can mask their presence. These tumors are seen within the jugular foramen; the demonstration of bone erosion of the jugular foramen and petrous apex is often a key finding in the diagnosis (see the image below). Careful review of bone windows is necessary.

Glomus tympanicum tumors are demonstrated in the images below.

Degree of confidence

The degree of confidence is high. The presence of strongly enhancing neck masses in typical perivascular locations leads to a high degree of confidence regarding the diagnosis.

False positives/negatives

Hypervascular lymphadenopathy may result in false-positive findings, which can be seen in a variety of disorders such as metastatic papillary carcinoma of the thyroid gland. In these instances, the location is a key finding.

The lack of sufficient contrast enhancement can be troublesome and may result in false-negative findings. In this case, glomus tumors can mimic schwannomas, neurofibromas, or nonenhancing lymphadenopathies. Potentially, small vascular tumors can be missed if they are not easily distinguishable from the adjacent vascular structures.

Similar to CT imaging, contrast-enhanced MRI demonstrates enhancing soft-tissue masses at characteristic locations; these findings are important for diagnosis. Nonenhanced MRI can demonstrate glomus tumors, but the demonstration of a strongly enhancing mass is typical in the diagnosis of a glomus tumor.^{[18, 19, 20]}

As with most soft-tissue tumors, glomus tumors are isointense on T1-weighted MRIs and hyperintense on T2-weighted MRIs, relative to skeletal muscle (see the images below).

Contrast-enhanced imaging can show intense tumor enhancement, which again is a key finding in the diagnosis. In addition, a salt-and-pepper fine vascular pattern can be seen in the tumors; this finding is suggestive of intrinsic tumor neovascularity and is particularly well demonstrated on T2-weighted images (see the image below).

MRIs can show densely enhancing carotid body tumors at the level of the carotid bifurcation, which respectively splay the internal and external carotid arteries medially and laterally (see the images below).

Glomus jugulare tumors are particularly well demonstrated by using MRI, which can show that enhancing soft-tissue masses protrude both intracranially and extracranially at the skull base. Direct coronal imaging can show tumoral relationships to adjacent structures such as the brainstem and skull base, and deep cervical soft-tissue structures are extraordinarily well depicted.

Degree of confidence

The degree of confidence is high. Tumor allocation and intense tumor enhancement are of paramount importance in diagnosis.

False positives/negatives

Hypervascular lymphadenopathy may result in false-positive findings, which can be seen in a variety of disorders such as metastatic papillary carcinoma of the thyroid gland. In particular, MRI findings can be confusing if T2-weighted images show a salt-and-pepper pattern. In such instances, the location is a key finding.

As with CT imaging, the lack of sufficient contrast enhancement can be troublesome and may result in false-negative findings. In this case, glomus tumors can mimic schwannomas, neurofibromas, or nonenhancing lymphadenopathies if an insufficient amount of contrast material is administered. Potentially, small vascular tumors can be missed if they are not clearly distinguishable from the adjacent vascular structures.

Doppler ultrasonography can demonstrate cervical masses when they are imaged below the angle of the mandible, above the sternum, or in a superficial location not hidden by bone. Ultrasonography can demonstrate the extent of the masses and show their locations. In glomus tumors, the diagnosis of carotid body tumors is possible with ultrasonographic cervical imaging, but this modality does not suitably reveal the location of glomus vagale, jugulare, and tympanicum tumors.

Because of tumor neovascularity, Doppler ultrasonographic sampling of cervical masses, such as carotid body tumors, can be helpful in the diagnosis. In addition, if recognized, increased flow velocities in the external carotid artery or in the jugular vein can provide an indirect clue to the diagnosis of a vascular mass that is above the ultrasonographic imaging field.

The degree of confidence is high if these tumors are found by using ultrasonography. Hypervascular lymphadenopathy can mimic a glomus tumor and cause a false-positive result. Many glomus tumors are seen in the neck above the level of the mandibular angle, rendering the diagnosis impossible with the use of ultrasonography alone; a false-negative finding can result.

Glomus tumors of the head and neck are typically highly vascular, as shown on angiograms. This finding differentiates them from other types of neck neoplasia (see the images below).

Typical carotid body tumors are situated in the carotid bifurcation and derive their arterial supply from regional external carotid branch arteries. These include the ascending pharyngeal and occipital arteries.

Glomus vagale and jugulare tumors are encountered higher in the neck and at the skull base; therefore, these masses concomitantly involve higher external carotid branch vessels (see the images below).

The ascending pharyngeal, tympanic, and occipital arteries dominate the arterial blood supply. The neovascularity may be extremely intense, and arteriovenous fistulae may be present. Rarely, the internal carotid and vertebral arteries may contribute feeders to the neoplasms. Typically, these tumors are evaluated, with attention paid to all potential feeding arteries. Care is taken to evaluate occult contralateral or ipsilateral masses, which can be occasionally overlooked during cross-sectional imaging.

The degree of confidence is high. The hallmark of a glomus tumor is its intrinsic neovascularity. At times, lymph node neovascularity can be difficult to differentiate from glomus tumors. In these situations, the location is a key feature.