Keywords carotid body tumor - carotid space paraganglioma - CT angiography - neck masses
Introduction
Carotid body is one of the sites of a group of paraganglia and receives its blood
supply mostly from the carotid bifurcation and the external carotid artery (ECA).[1 ]
Carotid body tumor (CBT), the most common paraganglioma of the neck, is a rare benign
tumor arising from the carotid body.[2 ]
[3 ]
[4 ] Radiological evaluation of CBTs ranges from ultrasonography, computed tomography
(CT) scan, magnetic resonance imaging, to mildly invasive evaluations like diagnostic
angiography.
On CT scans, these present as soft tissue lesions at the carotid bifurcation in the
carotid space, causing the internal (ICA) and ECAs to splay apart with intense and
homogenous enhancement on postcontrast scans.[3 ] While most studies have reported their findings based on the parenchymal phase,
none of the studies have commented on its enhancement pattern on CT angiography.
We present a case series of three cases of CBT who underwent CT angiography showing
a newly described enhancement pattern on CT angiography that might help in diagnosis
of CBTs.
Cases
Case 1
A 44-year-old female patient presented with complaints of painless swelling on the
left side of the neck for 1 year. On examination, the swelling was firm in consistency
with thrill on palpation.
Ultrasonography showed a well-defined lesion adjacent to the carotid artery with significantly
increased vascularity on color Doppler.
The patient was subjected to CT angiography. The angiogram phase was taken as soon
as the tracker region of interest, placed at the arch reached 120 Hounsfield Unit
threshold. Delayed phase was taken after 1 minute of the angiogram phase. CT showed
a well-defined hypodense soft tissue lesion in left carotid space ([Fig. 1 ]). The lesion showed peripheral thick rind of enhancement with central area encasing
the ICA showing no significant enhancement giving a central nonenhancement sign. The
patient was taken up for surgery and tumor was removed with graft replacement of the
involved ICA. Histopathology of the tumor showed features of CBT.
Fig. 1 Left carotid body tumor. A well-defined peripherally enhancing lesion at the carotid
bifurcation encasing the left internal carotid artery (straight arrow) and displacing
left external carotid artery anteromedially (curved arrow) showing central nonenhancement
sign.
Case 2
A 21-year-old male patient presented with a painless swelling on the left side of
his neck, below the angle of mandible, which had been present for past 8 months. On
examination, a firm, pulsatile, and nontender swelling was detected just below the
angle of mandible on the left side.
CT angiography revealed a well-defined enhancing lesion located at the left carotid
bifurcation characterized by central nonenhancement and peripheral rind of enhancement
([Fig. 2 ]) The ICA was encased by the lesion with ECA at the periphery of the tumor. The tumor
was surgically removed and subsequently diagnosed as CBT on histopathology.
Fig. 2 Left carotid body tumor. A well-defined peripherally enhancing tumor in left carotid
bifurcation showing central nonenhancement sign (arrow). Note the encased internal
carotid artery and displaced external carotid artery.
Case 3
A 65-year-old male patient presented with complaints of swelling on the right side
of the neck. CT angiography ([Fig. 3 ]) showed bilateral enhancing tumors at the carotid bifurcation. The larger CBT on
the right side encased the right ICA and ECA and exhibited a more heterogenous enhancement
pattern. The smaller tumor on the left side showed peripheral enhancement with central
nonenhancing area on CT angiography.
Fig. 3 (A ) Bilateral carotid body tumor showing peripheral enhancement on computed tomography
angiography; note the smaller tumor at left carotid bifurcation (arrow in B ) showing peripheral enhancement in arterial phase with central nonenhancement sign.
Discussion
Typically described findings for CBTs on postcontrast scans include a well-defined
lesion at carotid bifurcation, leading to the splaying of the carotid arteries and
showing intense, homogenous enhancement. However, enhancement pattern of CBTs on CT
angiography does not usually exhibit the intense, homogenous pattern, as seen in our
case series. We describe a new enhancement pattern of CBTs on CT angiography that
features a central area of nonenhancement. Possible explanation for this unique enhancement
pattern of CBTs can be as follows:
The predominant blood supply to the carotid body, and consequently the tumor, originates
from the carotid bifurcation and ECA. However, as the ICA is often the one that is
completely encased, the branches of ECA supplying the highly vascular tumor may enter
from the periphery, resulting in peripheral enhancement ([Fig. 1 ]).
Furthermore, with the advancement of CT machines, newer and faster scanner can scan
the lesion more rapidly, allowing less time for the entire tumor to enhance. As a
result, the peripheral part receives the initial bulk of the contrast, displaying
enhancement and creating a central nonenhancement sign.
These reasons can be further strengthened by the fact that when delayed images (acquired
1 minute after the angiography phase) of the cases mentioned above were analyzed,
the lesion showed uniform enhancement, thus ruling out the possibility of nonenhancing
necrotic areas ([Fig. 4 ]).
Fig. 4 (A ) The peripherally enhancing carotid body tumor on left side that on delayed phase
(B ) showing uniform enhancement with no central nonenhancing necrotic areas. (C ) Left small carotid body tumor (arrow) showing peripheral enhancement and uniform
enhancement on delayed phase (arrow in D ) ruling out the possibility of central nonenhancement sign only in large tumors.
Shamblin[5 ] in 1971 came up with a classification system that divides tumor based on their relationship
with the surrounding vessels, correlating this with surgical difficulty encountered
during tumor resection. While they did mention the encasement of the carotid arteries
by the tumor, they did not comment on the involvement of ECA in comparison to the
ICA.
To our knowledge, no study to date has reported the incidence of the involvement of
the ECA compared to the ICA in CBTs. It is conceivable that tumors encasing the distal
ICA with arterial supply from ECA may predominantly show this characteristic sign.
However, a more extensive study with a larger cohort of CBT patients is necessary
to analyze the incidence of involvement of each vessel. Furthermore, it is important
to examine the presence of this sign in patients with different combinations of carotid
artery involvement (i.e., other than the predominant encasement of ICA as compared
to ECA observed in the reported cases). A larger series of CBT cases should be investigated
to assess the diagnostic capabilities of the “central nonenhancement” sign on CT angiography
for identifying the CBTs and differentiating them from other lesions in the carotid
space.
Conclusion
CT angiography in three cases of CBTs shows this newly described sign of central nonenhancement
that may be useful in identifying CBTs.
