Imaging has a role in the diagnosis, evaluation of the extent of disease, follow-up and surgical planning. The anatomic location, displacement of surrounding vessels and skull base involvement allow accurate diagnosis of the type of paraganglioma.

Ultrasound is commonly employed in the early stages of diagnosis of a neck mass, and in these cases a heterogeneously hypoechoic mass is typically observed (Figure 1), accompanied by pronounced internal vascularity on color Doppler.

Fig 1: Heterogeneous hypoechoic mass at the level of the right common carotid artery bifurcation, with internal vascularity on color Doppler.

Magnetic resonance (MR) imaging is the most sensitive modality to characterize these lesions, which due to their vascular nature will typically demonstrate a “salt and pepper” appearance, relating to the presence of intratumoral hemorrhage and flow voids (Figure 2).  This appearance is, however, most apparent in tumors larger than 1 cm. After administration of intravenous (IV) gadolinium contrast agent, most frequently they present avid and homogeneous enhancement (Figure 2C).

Fig 2: Axial T2WI (A) and T1WI (B) in the same patient from figure 1. Well defined mass (blue arrows) at the right carotid artery bifurcation, between the internal (red arrows) and external (green arrows) carotid arteries. The mass is slightly heterogeneous, with multiple punctiform flow voids, as well as mild hyperintense areas in the T1WI. After IV gadolinium, homogeneous enhancement of the mass is seen (C). The splaying of internal and external carotid arteries results in the characteristic “lyre sign” (D). These findings are compatible with a carotid body paraganglioma.

Computed tomography (CT) is useful in the case of paragangliomas involving the skull base, as it helps to evaluate the involvement of key bony structures, and to guide management. On CT, they most commonly present as a homogeneous soft tissue mass that avidly enhances after administration of IV contrast [1,3].

CT/MR angiography or digital subtraction angiography may be useful in the preoperative setting, to identify feeding vessels for planning of subsequent embolization or surgery, as well as to demonstrate the presence of multicentric disease [3].

PET/CT is recommended in patients with known metastatic disease, or when at high risk for metastasis and/or multifocal disease, as it shows superior lesion detectability when compared to CT and MR.

Accurate diagnosis of the type of head and neck paraganglioma is possible taking into consideration the anatomic location, pattern of vessel displacement, and skull base involvement.

The most common location for paragangliomas in the head and neck is in the carotid body, at the carotid bifurcation, with splaying of the internal and external carotid arteries (Figure 2). The splaying of these vessels is referred to as the “lyre sign” (Figure 2D). When large enough, it can compress the adjacent nerves, resulting in dysphagia, hoarseness, or Horner’s syndrome. They are most often unilateral, but bilateral lesions can be seen in approximately 18% of patients (Figure 3). The relationship with the carotid arteries, according to the Shamblin classification, predicts resectability and risk of blood loss during surgical resection [1,3].

Fig 3: Same patient as in figure 2. Axial CT (A) and T1 WI before (B) and post-gadolinium (C) at a higher plane in relation to figure 2, where besides the known paraganglioma on the right (*), another paraganglioma (blue arrows) splaying the left internal (red arrows) and external (green arrows) carotid arteries can now also be seen. This patient had a SHDH mutation, which is associated with a higher risk of multifocal primary disease.

The main differential diagnosis to consider in cases where a mass is seen in this location is a peripheral nerve sheath tumor (schwannoma or neurofibroma) (Figures 4, 5). These tumors are generally less vascular and are not expected to show a “salt and pepper” appearance. The vascular behavior of the lesion can be better ascertained in a dynamic contrast-enhanced MR, where a paraganglioma will usually show a high peak enhancement with a short time-to-peak, while a schwannoma will demonstrate a low peak enhancement with a long time-to-peak. The pattern of vessel displacement also differs as, for example, a vagal schwannoma will generally splay the internal jugular vein and internal carotid artery, the latter being displaced anteromedially [3-5].

Fig 4: Axial (A) and sagittal (B) CT, axial T2WI (C), and T1WI before (D) and after (E) IV contrast agent, demonstrating a slightly heterogeneous mass (blue arrows) in the left carotid space, with no “salt and pepper” appearance. It flattens and displaces the internal jugular vein (yellow arrow) anteriorly, displaces the carotid vessels (red arrows) medially, and no “lyre sign” is seen in the sagittal plane. T1W fat-saturated images of a dynamic study in arterial phase (F) and venous phase (G), demonstrating gradual enhancement of the mass, which is more pronounced in a latter phase. This is not what we expect to see in the case of a paraganglioma, but instead in what was later confirmed to be a schwannoma.

Fig 5: Parapharyngeal schwannoma. Axial CT (A), T2WI (B), T1WI before (C) and post-contrast agent administration (D – axial and E – coronal), demonstrating a large heterogeneous and enhancing mass (blue arrows) in the parapharyngeal space, which displaces and narrows the oropharynx (brown arrows), and displaces the internal carotid artery anterolaterally (red arrow). The mass was separated from the deep parotid lobe (not shown). No intralesional flow voids.

Another differential consideration is a hypervascular metastasis, where a “salt and pepper” appearance can also be seen. This should especially be considered in patients with known malignancy, such as thyroid or renal cell carcinoma (Figure 6) [3].

Fig 6: Axial CT (A), coronal T2WI (B) and T1WI before (C) and after gadolinium contrast agent (D, in axial plane), showing an enhancing mass in the right carotid space (blue arrows), with a “salt and pepper” appearance, splaying the internal and external carotid arteries (red arrows, most evidently seen on D), however, the mass is located slightly more posterior than what we would expect to see in a typical carotid body tumor. This was a patient with known renal cell carcinoma, and the lesion was later confirmed as a metastasis.

Vagal paragangliomas are less common than carotid body or jugular paragangliomas. While presenting most commonly as a slow growing painless mass, they may cause hoarseness due to vocal cord paralysis. The typical location is below the skull base and above the carotid bifurcation, although they can occur anywhere along the course of the vagus nerve. The tissue characteristics are similar to the carotid body paraganglioma, but the mass effect on the vessels differs from it, as the posterolateral position of the vagus nerve in relation to the internal and external carotid arteries results in displacement of those vessels together anteromedially, and the jugular vein posterolaterally (Figure 7). CT is of particular importance in cases of high vagal paragangliomas, to evaluate for bone involvement of the cranial base. The main differential diagnosis is a vagal schwannoma or neurofibroma [1,3].

Fig 7: Axial T2WI (A) and T1WI before (B) and after (C) gadolinium contrast agent, showing a T2 and T1 hypointense and enhancing lesion (blue arrow) with “salt and pepper” appearance in the right carotid space, above the level of the common carotid artery bifurcation. The internal carotid artery is slightly displaced anteromedially (red arrow), and the internal jugular vein posterolaterally (yellow arrow), compatible with a vagal paraganglioma. Axial image from a 18F-FDG PET/CT (D) showing lung metastases (white arrows). This was a patient with SDHD mutation, with bilateral vagal paragangliomas (the left not shown), a right carotid paraganglioma (not shown), and diffuse metastatic disease.

Jugular paragangliomas are the most common tumor found in the jugular foramen, and the second most common head and neck paraganglioma. Clinically, they most often present with hearing loss or unilateral tinnitus. They expand aggressively into the temporal bone, in later stages presenting with bony erosion and a “moth-eaten” appearance of the temporal bone. Extension into the middle ear may occur, as its presence indicates a jugulotympanic paraganglioma (Figure 8).  In such cases, usually it is not clear whether the tumor originates from the jugular fossa or the middle ear, and they most commonly present as pulsatile tinnitus, and in some cases IX and X cranial nerves deficits. When evaluating for jugular or jugulotympanic paragangliomas, both CT and MR are indicated, as the former allows for assessment of the osseous involvement for preoperative planning, and the latter is more sensitive for intracranial extension.

Fig 8: Patient presented with a pulsatile reddish nodule behind the tympanic membrane. On CT (A and B), an irregular erosive mass (blue arrows in A) was seen in the left jugular foramen, extending into the middle ear, where a nodular component was visible (blue arrow in B), corresponding to the nodule seen in the physical exam. On MR (T1WI before – C – and after IV contrast – D and E), this corresponded to a T1 hypointense enhancing mass (blue arrows), with no intracranial extension. This was a jugulotympanic paraganglioma.

The differential diagnosis of jugular paragangliomas includes other tumors originating or extending through the jugular fossa, most often schwannomas, neurofibromas, or meningiomas [1,3,6]. Peripheral neural sheath tumors are usually well-delineated enhancing lesions (Figure 9), unlike jugular paragangliomas which expand aggressively and have irregular margins. Another distinguishing feature is that neural sheath tumors usually compress the jugular vein, while jugular paragangliomas may invade it. Flow voids are not a clearly distinguishing feature, as they can be seen in certain vascular schwannomas.

Fig 9: Schwannoma. T2WI (A), T1W1 before (B) and after (C and D) IV contrast showing a well-delineated and enhancing lesion (blue arrows) in the left jugular fossa, and extending inferiorly to it along the carotid space, with a central cystic component. Notice the compression of the internal jugular vein (yellow arrow).

As for meningiomas, the presence of hyperostosis (which is typical for meningiomas that abut the cranial base) and the pattern of spread are some of the findings that help in the differential diagnosis (Figure 10). While jugular paragangliomas typically extend into the hypotympanum, with only limited involvement of the carotid space inferiorly, meningiomas may extend inferiorly into the nasopharynx and the carotid space (Figure 11) [3,6].

Fig 10: Meningioma. T1WI before (A) and after (B and C) IV contrast, demonstrating a broadly-based lesion in the left cerebellopontine angle (blue arrows), homogeneously enhancing, and extending through the jugular foramen. Limited extension into the porus acousticus internus (light blue arrow). Associated signal changes of the bone marrow of the left occipital condyle and clivus (orange arrow).

Fig 11: Meningioma. T1WI after IV contrast (A and B) demonstrating a bulky homogeneously enhancing lesion (blue arrows) that extends through the right jugular foramen (light blue arrow) until just cranially to the common carotid artery bifurcation (surrounding the internal and external carotid arteries – red arrows), and into the posterior cervical space. Associated deviation and narrowing of the oro/hypopharynx (brown arrow). In the CT (C), hyperostosis of the right temporal bone (orange arrows) is seen.

Tympanic paragangliomas are the most common tumor of the middle ear, and 80-90% of patients are women. Clinically, they most often present with pulsatile tinnitus or unilateral hearing loss, and commonly a red pulsatile mass is seen within the middle ear on otoscopic examination. On imaging, a soft tissue mass in the cochlear promontory is seen, with no dehiscence or osseous erosion around the jugular bulb. Imaging allows to differentiate from an aberrant course of the internal carotid artery, which clinically may be undistinguishable from a tympanic paraganglioma, as its injury during surgery can result in significant morbidity [1,3].

CT is the modality of choice for its evaluation, but MR may be useful to differentiate it from mimics such as inspissated secretions, cholesteatomas, or other tumors of the middle ear. Tympanic paragangliomas markedly enhance after contrast (Figure 12) due to their highly vascular nature, which helps to differentiate them from inspissated secretions or cholesteatomas, which don’t enhance.

Fig 12: Tympanic paraganglioma. On the CT images (A - coronal plane and B – axial plane), a soft tissue nodule (blue arrows) in the middle ear, with a broad base against the cochlear promontory (orange arrows) is seen. No bony erosion or dehiscence of the jugular bulb (not shown). On MR (C – T1WI before IV contrast; D – T1WI after IV contrast), enhancement after IV contrast administration is seen (blue arrows). The localization is typical for a tympanic paraganglioma.

The typical location of the tympanic paraganglioma at the cochlear promontory, as well as its pulsatile nature, which is not seen in other middle ear tumors such as a schwannoma or an adenoma, also help in the differential diagnosis (Figure 13) [3,7,8].

Fig 13: Patient presented with a non-pulsatile swelling in the middle ear. On CT (A), a polypoid opacification of the middle ear was seen (blue arrow), as well as opacification of the mastoid air cells (light blue arrow). It contacts the ossicle chain (orange arrow), but with no associated bony erosion. On MR (T1WI before and after IV contrast, respectively B and C), an enhancing soft tissue lesion (blue arrow) in the middle ear was seen, obstructing the aditus ad antrum, with secondary retro-obstructive fluid in the mastoid air cells (light blue arrow). The enhancement is slightly less marked than what would be expected to see in a tympanic paraganglioma. This was later confirmed to be a middle ear adenoma.