Doppler ultrasound appearance of neck tumors

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Polish Ultrasound Society (Polskie Towarzystwo Ultrasonograficzne)

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VOLUME 18 , ISSUE 73 (August 2018) > List of articles

Doppler ultrasound appearance of neck tumors

Anna Szymańska * / Marcin Szymański / Wiesław Gołąbek / Anna Drelich-Zbroja / Tomasz Jargiełło

Keywords : vascular malformation, paraganglioma, aneurysm, lipoma, Doppler ultrasound

Citation Information : Journal of Ultrasonography. Volume 18, Issue 73, Pages 96-102, DOI: https://doi.org/10.15557/JoU.2018.0014

License : (CC-BY-NC-ND-4.0)

Received Date : 24-January-2018 / Accepted: 16-April-2018 / Published Online: 31-August-2018

ARTICLE

ABSTRACT

Aim: The purpose of this study was the evaluation of the sonographic appearance of neck tumors and determining the features useful in differential diagnosis. Material and method: The studied group consisted of 57 patients: 16 patients with carotid body tumors, 9 patients with neurogenic tumors, 8 patients with venous anomalies, 12 patients with neck cysts, 6 patients with lipomas, 5 patients with extracranial carotid artery aneurysms and 1 with a laryngocele. Results: All carotid paragangliomas were located within the carotid bifurcation and demonstrated rich low-resistance vascular flow, with higher maximum velocity and lower flow resistance parameters registered in the ipsilateral external carotid artery. In 7 out of 9 cases, neurogenic tumors were homogeneous, and in the remaining 2 cases – heterogeneous. Four schwannomas were hypervascular or showed moderate vascularity, and the rest of neurogenic tumors were hypovascular or avascular, with symmetrical maximum velocity and resistance values of carotid blood flow. Apart from one branchial cleft cyst with multiple fine internal acoustic reflexes, all other neck cysts were anechoic and avascular, and presented with posterior acoustic enhancement. The laryngocele presented as a well-demarcated, hypoechoic, homogeneous lesion located in the immediate proximity of the larynx, without signs of internal vascular flow. Lipomas were well-demarcated, homogeneous, hypoechoic tumors with regular margins, without signs of internal vascular flow. Venous malformations presented as irregular, hypoechoic spaces with venous blood flow, easily compressed by the probe. Extracranial carotid artery aneurysms were hypoechoic, well-defined spaces, which presented with slow internal, turbulent flow on Doppler study, and showed continuity with the carotid artery. Conclusions: Doppler ultrasound allows to visualize features characteristic for certain neck tumors. Solid or cystic structure, echogenicity, localization, as well as internal flow signals and vascularity pattern create a combination of ultrasound findings helpful in the differential diagnosis of lesions such as paragangliomas, venous malformations, neurogenic tumors, aneurysms, cysts and laryngoceles.

Graphical ABSTRACT

Introduction

Ultrasound (US) is widely used for the evaluation of neck structures. Their relatively superficial localization makes them easily accessible for US evaluation, whose additional advantages include high diagnostic accuracy, common use in clinical practice, a lack of ionizing radiation exposure for the patient, relatively low cost compared with other imaging modalities and the possibility for real-time biopsy monitoring.

In patients with neck lesions, a detailed clinical history and physical examination usually facilitate a preliminary diagnosis. The role of imaging studies is to narrow down and finalize the diagnosis, and determine the extent of the lesion. US examination is the modality of choice for the evaluation of cervical structures.

The aim of this study was to analyze the US appearance of neck lesions with the use of Doppler technique, and to identify the characteristic findings allowing for an effective differential diagnosis.

Material and Method

A total of 57 patients with neck lesions were evaluated, comprising 16 patients with carotid paragangliomas (PGLs), 9 with neurogenic tumors (including 3 neurofibromas, 5 shwannomas and 1 sarcoma neurogenes), 8 patients with venous malformations, 12 with neck cysts, 6 with lipomas, 5 with extracranial carotid artery aneurysms and 1 with laryngocele.

All patients were examined with LOGIQ 7 GE Healthcare Medical System device, with a 7.5–11 MHz linear transducer. In selected patients with extensive lesions, further examination was performed with a 3.5–4.0 MHz convex transducer. In all patients, the evaluated parameters included the location and contour of the lesion, its echogenicity, echostructure and compressibility. Also, 51 patients were examined with Doppler ultrasound (DUS) for the presence of vascular flow within the lesion and its position to cervical vessels. In vascular solid masses, flow velocity and resistance index values were identified in the tumor’s vessels and carotid arteries.

All patients with solid tumors and neck cysts underwent surgery and the diagnosis was confirmed on the basis of histopathological exam. In patients with a venous malformation, magnetic resonance imaging (MRI) was performed to confirm a signal intensity pattern typical for this type of lesion. All extracranial carotid artery aneurysms were confirmed on CT or angiography.

Results

In all PGL patients, US scan showed the presence of a solid mass with regular margins and slightly inhomogeneous echogenicity, hypo- or isoechoic. All lesions were found in the carotid artery bifurcation, resulting with splaying of the internal and external carotid arteries of a varying degree, with the internal carotid artery dislocated posterolaterally. The maximal tumor diameter ranged from 2–5 cm. In color Doppler ultrasound (CDUS), all tumors presented with multiple flow signals characteristic for vascular pathologies (Fig. 1). In all patients investigated with color duplex DUS, the vascular flow within tumor vessels was characterized by low resistance, with mean resistivity index (RI) and pulsatility index (PI) being 0.5 and 0.7 respectively (Fig. 2). In 12 (approx. 75%) patients, the comparison of vascular flow parameters in both external carotid arteries showed higher velocity (mean Vmax = 1.5 m/s) and lower resistance (mean RI = 0.6 and PI = 0.8) in the carotid artery on the side where the tumor was located compared with the contralateral artery (mean Vmax = 1.0 m/s, mean RI = 0.8 and PI = 1.75) (Fig. 3).

Fig. 1.

PDUS of a richly vascular carotid PGL

10.15557_JoU.2018.0014-f001.jpg
Fig. 2.

Low-resistance pattern of vascular flow within a PGL

10.15557_JoU.2018.0014-f002.jpg
Fig. 3.

Low-resistance pattern of vascular flow within the ipsilateral external carotid artery compared to ipsilateral internal carotid artery

10.15557_JoU.2018.0014-f003.jpg

All neurogenic tumors presented as a well-defined, ovoid, solid, hypoechoic mass, with moderate posterior enhancement. In 7 patients, the tumors had homogeneous structure, and 2 showed inhomogeneous echogenicity and irregular contour. The maximal tumor diameter ranged from 1.5–6 cm. Three tumors were located in the posterior neck triangle, and 6 medially to neck vessels. Color Doppler investigation revealed rich or moderate vascularity in 4 schwannoma patients. In the remaining tumors, vascular flow signals were scarce (Fig. 4). In spectral Doppler, vascular flow values and resistance index values were similar (mean Vmax = 0.95 m/s, mean PI = 1.6 and RI = 0.65) in the ipsilateral vs. contralateral external carotid artery (Vmax = 0.9 ms, PI = 1.65 and RI = 0.7).

Fig. 4.

CDUS of a poorly vascular neurofibroma

10.15557_JoU.2018.0014-f004.jpg

Neck cysts in 2 patients presented as thyroglossal duct cysts and in 10 patients as branchial cleft cysts. All lesions were well-defined, thin-walled, with posterior acoustic enhancement and no vascular flow in a Doppler scan, with a diameter of 3–5 cm. Apart from one branchial cleft cyst, containing multiple fine, diffuse, internal reflexes, all the remaining lesions were anechoic (Fig. 5). All branchial cleft cysts were ovoid, had regular margins and were located alongside the sternocleidomastoid muscle. Thyroglossal duct cysts were found in the paramedian position, in the proximity of the hyoid bone, and had more irregular contours.

Fig. 5.

A well-defined, superficial, anechoic space with acoustic enhancement – typical branchial cleft cyst appearance

10.15557_JoU.2018.0014-f005.jpg

The laryngocele presented as a well-demarcated, hypoechoic, homogeneous lesion sized 2.5 × 3.5 cm, located in the anterolateral aspect of the neck, medially to the sternocleidomastoid muscle and neck vessels, next to the larynx. In a Doppler study, no vascular flow was visualized.

Lipomas were well-circumscribed, homogeneous, hypoechoic masses with regular contours and no vascular flow in Doppler evaluation. They were all located superficially, with a maximal diameter of 4 cm and 5 cm, respectively (Fig. 6).

Fig. 6.

A well-defined, solid, homogeneous tumor with slight posterior enhancement – consistent with lipoma

10.15557_JoU.2018.0014-f006.jpg

Venous malformations presented as longitudinal and circular anechoic spaces of irregular shape and well-defined contours (Fig. 7). One lesion presented as tortuous hypoechoic vascular channels. All malformations were situated superficially, displayed acoustic enhancement and were readily compressible. In a Doppler study, they showed turbulent venous flow (Fig. 8).

Fig. 7.

B-mode US of a venous malformation: superficial, well-defined, hypoechoic spaces of an irregular shape

10.15557_JoU.2018.0014-f007.jpg
Fig. 8.

DUS of venous vascular flow in a venous malformation

10.15557_JoU.2018.0014-f008.jpg

Extracranial carotid artery aneurysms were well-demarcated, hypoechoic spaces with a maximal diameter of 3–5 cm, communicating with the internal (3/5) or external carotid artery (2/5) (Fig. 9). All lesions showed peripheral thrombi. In Doppler examination, their lumen displayed turbulent, slowed vascular flow.

Fig. 9.

An extracranial carotid artery aneurysm presenting as a well-demarcated, hypoechoic space with peripheral thrombi, connected to the external carotid artery

10.15557_JoU.2018.0014-f009.jpg

Discussion

Neck tumors are commonly encountered in clinical practice, and are a very diverse group of lesions. Imaging studies play a very important role in noninvasive diagnostic workup, with US used as first-line modality. Multiplanar imaging with CT and MR can be used for further investigation, especially in the case of deep-situated and locally invasive masses, to confirm the diagnosis and accurately determine their extent prior to surgery(1). Even though US appearance of many lesions is nonspecific, a comprehensive analysis of their characteristics in many cases facilitates a correct diagnosis, or at least allows to narrow down the differential workup.

The lesion’s morphology is an important factor in its preliminary evaluation, allowing to differentiate solid masses from cystic lesions. The most common cystic formations are branchial cleft cysts, most of which arise from the remnants of the second branchial arch. They typically occur in children and young adults aged 20–40 years old(2). On US, the cyst presents as a well-defined, round or ovoid, thin-walled lesion, most typically anechoic, with pronounced posterior enhancement(2,3). Thyroglossal duct cysts are less common and occur at a younger age (16–25 years old)(4). Their US appearance is influenced by previous inflammatory or hemorrhagic episodes which may lead to the presence of internal reflexes, mimicking a solid mass, as was the case in one of the patients in this study. Additionally, thyroglossal duct cysts may present with internal septa, thickened walls and a blurred margin(4,5).

The sonographic appearance of laryngocele resembles that of a non-complicated cyst, which may lead to a misdiagnosis(2). In such circumstances, the localization of the lesion provides valuable insight. Branchial cleft cysts are situated superficially to neck vessels, along the medial and anterior border of the sternocleidomastoid muscle, whilst laryngoceles are clearly adjacent to the larynx (Fig. 10).

Fig. 10.

A well-defined, hypoechoic space with acoustic enhancement, adhering to the thyroid cartilage – an ultrasound appearance of a laryngocele

10.15557_JoU.2018.0014-f010.jpg

In the studied group, anechoic masses with acoustic enhancement included also extracranial carotid artery aneurysms and venous malformations. Doppler investigation plays a key role in distinguishing these vascular anomalies from neck cysts, facilitating adequate further diagnostics and treatment(1). Neck cysts do not show any vascular flow on a Doppler scan, whilst aneurysms present with multidirectional, tortuous flow, with turbulent spectral analysis (Fig. 11). Peripheral thrombi may also be noted. Additionally, in multiplanar evaluation it is usually possible to trace the course of the artery running through the lesion.

Fig. 11.

An external carotid artery aneurysm with visible turbulent vascular flow seen on CDUS (A) and PDUS (B)

10.15557_JoU.2018.0014-f011.jpg

Venous malformations, as opposed to isolated, well pronounced anechoic foci, tend to present as hypoechoic, confluent areas of irregular shape. They may also present as tortuous, poorly demarcated vascular channels(6), as observed in one of our patients. Spectral Doppler reveals venous flow. They are also characterized by their compressibility, as the venous vessels without thrombi are obliterated with light pressure from the probe. Approximately 15% of venous malformations are found in the head and neck region. Fine, strong reflexes with a posterior shadow represent phleboliths and confirm the diagnosis, although they are not always present (approx. 20% of cases)(6).

The echostructure of solid neck tumors varies. Our results are supported by literature data showing that carotid PGLs and neurogenic tumors typically present as well-circumscribed, mostly homogeneous lesions, with or without posterior acoustic enhancement(79). Also the lipomas investigated in our study had an US appearance of a homogeneous tumor. They are benign capsular lesions, usually located subcutaneously and to some extent compressible with moderate transducer pressure(10). The most common neurogenic neck and head tumors include schwannomas and neurofibromas. Some authors state that schwannomas may undergo cystic degenerative changes, and both types of the tumors may show a lobular structure, without marked acoustic enhancement(7,8,11,12). Such appearance was seen in two patients with neurofibromas in our group. Markedly inhomogeneous echogenicity is more commonly found in large tumors, as a result of degenerative changes(9). A pathognomic, although not always present, feature of neurogenic tumors is their direct connection to the thickened nerve(7).

Doppler evaluation of the vascularity of solid neck masses is an important part of the differential workup, as it allows to identify highly vascular lesions, providing the surgeon with very important preoperative information. The presence of numerous, tortuous vessels with turbulent, low-resistance flow is highly indicative of a PGL(13,14). Jin et al.(15) showed a statistically significant difference between the vascularity of nerve sheath tumors and carotid PGLs to the advantage of the latter, as well as low RI values for these masses. A comparative analysis of the vascular flow in both external carotid arteries additionally aids the diagnosis, as the majority of PGL patients show a decreased RI in the ipsilateral external carotid artery, due to the presence of arteriovenous fistulas within the lesion(13,16). The vascularity of neurogenic tumors seen on Doppler examination may range from minimal to abundant(7,8). King et al.(8) and Kami et al.(7) state that schwannomas are highly vascular, and tumor vessels can be easily obliterated with light pressure from the probe. In our study, 5 schwannomas were moderately or richly vascular, without a decreased RI in the ipsilateral external carotid arteries.

In the case of a highly vascular neck tumor, analysis of its location may be helpful for differential diagnosis. A large majority of authors consider tumor location as an important predictor in the diagnostic workup(1,9,17,18). The location in the carotid artery bifurcation, with the lesion splaying the proximal aspects of the internal and external carotid arteries (Fig. 12), and the internal carotid artery dislocated posterolaterally (wineglass bifurcation/lyre sign), is pathognomic for a PGL(12,19,20). Characteristic findings include a solitary nodule in this location, or in the case of multiple paragangliomas, bilateral solitary nodules situated symmetrically in the carotid bifurcations. In our study, all PGLs were found in their typical location. Neurogenic tumors located in the proximity of carotid vessels were situated medially to the vascular bundle, dislocating it laterally (Fig. 13), whereas all branchial cleft cysts were situated superficially to carotid vessels (Fig. 14).

Fig. 12.

A hypoechoic PGL situated in the carotid bifurcation, splaying the proximal aspects of its branches

10.15557_JoU.2018.0014-f012.jpg
Fig. 13.

Sarcoma neurogenes: visible absence of vascular flow and the tumor’s medial location to carotid arteries

10.15557_JoU.2018.0014-f013.jpg
Fig. 14.

CDUS of a well-defined, avascular cyst, located superficially to neck vessels, with visible fine internal reflexes and acoustic enhancement

10.15557_JoU.2018.0014-f014.jpg

Conclusions

Ultrasound evaluation using colour and spectral Doppler modality visualizes certain characteristic features of given neck tumor types. Findings such as solid vs cystic content, characteristic echostructure and location, the presence of vascular flow and the pattern of vasculature make up various combinations forming ultrasound appearances helpful in the differential diagnosis of paragangliomas, venous malformations, neurogenic tumors, aneurysms, cysts and laryngoceles.

Conflict of interest

The authors do not declare any financial or personal links to other persons and organizations that could adversely affect the content of this publication and/or claim rights thereto.

References


  1. Griauzde J, Srinivasan A: Imaging of vascular lesions of the head and neck. Radiol Clin North Am 2015; 53: 197–213.
    [CROSSREF]
  2. Nowak K: Przydatność badania ultrasonograficznego w diagnostyce wrodzonych torbieli bocznych i środkowych szyi. Otolaryngol Pol 2000; 54: 751–761.
    [PUBMED]
  3. Ahuja AT, King AD, Metreweli C: Second branchial cleft cysts: Variability of sonographic appearances in adult cases. AJNR Am J Neuroradiol 2000; 21: 315–319.
    [PUBMED]
  4. Zajkowski P, Piórkowska K, Postolski M: Ocena wyników badania ultrasonograficznego u chorych z torbielami bocznymi i środkowymi szyi. Ultrason Pol 1996; 6: 81–86.
  5. Flanagen P, Roland N, Jones A: Cervical node metastases presenting with features of branchial cysts. J Laryngol Otol 1994; 108: 1068–1071.
    [PUBMED] [CROSSREF]
  6. Ahuja AT, Richards P, Wong KT, Yuen EH, King AD: Accuracy of high-resolution sonography compared with magnetic resonance imaging in the diagnosis of head and neck venous vascular malformations. Clin Radiol 2003; 58: 869–875.
    [CROSSREF]
  7. Kami YN, Chikui T, Okamura K, Kubota Y, Oobu K, Yabuuchi H et al.: Imaging findings of neurogenic tumors in the head and neck. Dentomaxillofac Radiol 2012; 41: 18–23.
    [CROSSREF]
  8. King AD, Ahuja AT, King W, Metreweli C: Sonography of peripheral nerve tumors of the neck. AJR Am J Roentgenol 1997; 169: 1695–1698.
    [CROSSREF]
  9. Demattè S, Di Sarra D, Schiavi F, Casadei A, Opocher G: Role of ultrasound and color Doppler imaging in the detection of carotid paragangliomas. J Ultrasound 2012; 15: 158–163.
    [CROSSREF]
  10. Ahuja AT, King AD, Kew J, King W, Metreweli C: Head and neck lipomas: Sonographic appearance. AJNR Am J Neuroradiol 1998; 19: 505–508.
    [PUBMED]
  11. Fornage BD: Sonography of peripheral nerves of the extremities. Radiol Med 1993; 85 (Suppl. 1): 162–167.
    [PUBMED]
  12. Knulst R, Bosman WM, Ritchie ED, da Costa A: Cystic schwannoma of the recurrent laryngeal nerve: A rare finding posing diagnostic difficulties. BMJ Case Rep 2014; 2014: bcr2014203873.
  13. Szymańska A, Jargiełło T, Drelich-Zbroja A, Szczerbo-Trojanowska M: Ultrasonografia duplex Doppler w ocenie przyzwojaków podziału tętnicy szyjnej wspólnej. Ultrasonografia 2001; 7: 26–31.
  14. Derchi LE, Serafini G, Rabbia C, De Albertis P, Solbiati L, Candiani F et al.: Carotid body tumors: US evaluation. Radiology 1992; 182: 457–459.
    [CROSSREF]
  15. Jin ZQ, He W, Wu DF, Lin MY, Jiang HT: Color Doppler ultrasound in diagnosis and assessment of carotid body tumors: Comparison with computed tomography angiography. Ultrasound Med Biol 2016; 42: 2106–2113.
    [CROSSREF]
  16. Barry P, Pienaar A, Pienaar C, Browning NG, Nel CJ: Duplex Doppler investigation of suspected vascular lesion at the carotid bifurcation. Ann Vasc Surg 1993; 7: 140–144.
    [CROSSREF]
  17. Najeeb T, Khan MJ: Sympathetic chain schwannoma resembling carotid body tumour. J Coll Physicians Surg Pak 2016; 26 (Suppl.): S68–S70.
    [PUBMED]
  18. Lee RM, Ong CP, Jacobsen AS, Chan MY, Hwang WS: Malignant peripheral nerve sheath tumor mimicking carotid body tumor – case report and review. J Pediatr Surg 2011; 46: 554–558.
    [CROSSREF]
  19. Myers EN, Johnson JT, Neoplasms. In: Cummings CW, Fredricson JM, Harker LA, Krause CJ, Richardson MA, Schuller DE (eds.): Otolaryngology – Head and Neck Surgery. Mosby Year Book, St Louis 1993: 1590–1604.
  20. Steinke W, Hennerici M, Aulich A: Doppler color flow imaging of carotid body tumors. Stroke 1989; 20: 1574–1577.
    [CROSSREF]
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FIGURES & TABLES

Fig. 1.

PDUS of a richly vascular carotid PGL

Full Size   |   Slide (.pptx)

Fig. 2.

Low-resistance pattern of vascular flow within a PGL

Full Size   |   Slide (.pptx)

Fig. 3.

Low-resistance pattern of vascular flow within the ipsilateral external carotid artery compared to ipsilateral internal carotid artery

Full Size   |   Slide (.pptx)

Fig. 4.

CDUS of a poorly vascular neurofibroma

Full Size   |   Slide (.pptx)

Fig. 5.

A well-defined, superficial, anechoic space with acoustic enhancement – typical branchial cleft cyst appearance

Full Size   |   Slide (.pptx)

Fig. 6.

A well-defined, solid, homogeneous tumor with slight posterior enhancement – consistent with lipoma

Full Size   |   Slide (.pptx)

Fig. 7.

B-mode US of a venous malformation: superficial, well-defined, hypoechoic spaces of an irregular shape

Full Size   |   Slide (.pptx)

Fig. 8.

DUS of venous vascular flow in a venous malformation

Full Size   |   Slide (.pptx)

Fig. 9.

An extracranial carotid artery aneurysm presenting as a well-demarcated, hypoechoic space with peripheral thrombi, connected to the external carotid artery

Full Size   |   Slide (.pptx)

Fig. 10.

A well-defined, hypoechoic space with acoustic enhancement, adhering to the thyroid cartilage – an ultrasound appearance of a laryngocele

Full Size   |   Slide (.pptx)

Fig. 11.

An external carotid artery aneurysm with visible turbulent vascular flow seen on CDUS (A) and PDUS (B)

Full Size   |   Slide (.pptx)

Fig. 12.

A hypoechoic PGL situated in the carotid bifurcation, splaying the proximal aspects of its branches

Full Size   |   Slide (.pptx)

Fig. 13.

Sarcoma neurogenes: visible absence of vascular flow and the tumor’s medial location to carotid arteries

Full Size   |   Slide (.pptx)

Fig. 14.

CDUS of a well-defined, avascular cyst, located superficially to neck vessels, with visible fine internal reflexes and acoustic enhancement

Full Size   |   Slide (.pptx)

REFERENCES

  1. Griauzde J, Srinivasan A: Imaging of vascular lesions of the head and neck. Radiol Clin North Am 2015; 53: 197–213.
    [CROSSREF]
  2. Nowak K: Przydatność badania ultrasonograficznego w diagnostyce wrodzonych torbieli bocznych i środkowych szyi. Otolaryngol Pol 2000; 54: 751–761.
    [PUBMED]
  3. Ahuja AT, King AD, Metreweli C: Second branchial cleft cysts: Variability of sonographic appearances in adult cases. AJNR Am J Neuroradiol 2000; 21: 315–319.
    [PUBMED]
  4. Zajkowski P, Piórkowska K, Postolski M: Ocena wyników badania ultrasonograficznego u chorych z torbielami bocznymi i środkowymi szyi. Ultrason Pol 1996; 6: 81–86.
  5. Flanagen P, Roland N, Jones A: Cervical node metastases presenting with features of branchial cysts. J Laryngol Otol 1994; 108: 1068–1071.
    [PUBMED] [CROSSREF]
  6. Ahuja AT, Richards P, Wong KT, Yuen EH, King AD: Accuracy of high-resolution sonography compared with magnetic resonance imaging in the diagnosis of head and neck venous vascular malformations. Clin Radiol 2003; 58: 869–875.
    [CROSSREF]
  7. Kami YN, Chikui T, Okamura K, Kubota Y, Oobu K, Yabuuchi H et al.: Imaging findings of neurogenic tumors in the head and neck. Dentomaxillofac Radiol 2012; 41: 18–23.
    [CROSSREF]
  8. King AD, Ahuja AT, King W, Metreweli C: Sonography of peripheral nerve tumors of the neck. AJR Am J Roentgenol 1997; 169: 1695–1698.
    [CROSSREF]
  9. Demattè S, Di Sarra D, Schiavi F, Casadei A, Opocher G: Role of ultrasound and color Doppler imaging in the detection of carotid paragangliomas. J Ultrasound 2012; 15: 158–163.
    [CROSSREF]
  10. Ahuja AT, King AD, Kew J, King W, Metreweli C: Head and neck lipomas: Sonographic appearance. AJNR Am J Neuroradiol 1998; 19: 505–508.
    [PUBMED]
  11. Fornage BD: Sonography of peripheral nerves of the extremities. Radiol Med 1993; 85 (Suppl. 1): 162–167.
    [PUBMED]
  12. Knulst R, Bosman WM, Ritchie ED, da Costa A: Cystic schwannoma of the recurrent laryngeal nerve: A rare finding posing diagnostic difficulties. BMJ Case Rep 2014; 2014: bcr2014203873.
  13. Szymańska A, Jargiełło T, Drelich-Zbroja A, Szczerbo-Trojanowska M: Ultrasonografia duplex Doppler w ocenie przyzwojaków podziału tętnicy szyjnej wspólnej. Ultrasonografia 2001; 7: 26–31.
  14. Derchi LE, Serafini G, Rabbia C, De Albertis P, Solbiati L, Candiani F et al.: Carotid body tumors: US evaluation. Radiology 1992; 182: 457–459.
    [CROSSREF]
  15. Jin ZQ, He W, Wu DF, Lin MY, Jiang HT: Color Doppler ultrasound in diagnosis and assessment of carotid body tumors: Comparison with computed tomography angiography. Ultrasound Med Biol 2016; 42: 2106–2113.
    [CROSSREF]
  16. Barry P, Pienaar A, Pienaar C, Browning NG, Nel CJ: Duplex Doppler investigation of suspected vascular lesion at the carotid bifurcation. Ann Vasc Surg 1993; 7: 140–144.
    [CROSSREF]
  17. Najeeb T, Khan MJ: Sympathetic chain schwannoma resembling carotid body tumour. J Coll Physicians Surg Pak 2016; 26 (Suppl.): S68–S70.
    [PUBMED]
  18. Lee RM, Ong CP, Jacobsen AS, Chan MY, Hwang WS: Malignant peripheral nerve sheath tumor mimicking carotid body tumor – case report and review. J Pediatr Surg 2011; 46: 554–558.
    [CROSSREF]
  19. Myers EN, Johnson JT, Neoplasms. In: Cummings CW, Fredricson JM, Harker LA, Krause CJ, Richardson MA, Schuller DE (eds.): Otolaryngology – Head and Neck Surgery. Mosby Year Book, St Louis 1993: 1590–1604.
  20. Steinke W, Hennerici M, Aulich A: Doppler color flow imaging of carotid body tumors. Stroke 1989; 20: 1574–1577.
    [CROSSREF]

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