TOS is a compression syndrome that could be classified as the VTOS which is considered less frequent than the NTOS; VTOS had been further subdivided anatomically into three compartments where the compression could take place, and those are the scalene triangle, the costo-clavicular space, and the retro-pectoral space [1,2,3].
The present study was concerned with the description of the ultrasound findings in cases of VTOS by dynamic duplex examination and detection of the complication of long-standing compression.
By dynamic duplex examination, venous compression was the predominating type of VTOS in this study being found in (84.4%) of the patients; bilateral affection was also a predominating feature being observed in (94.4%) of the patients; nevertheless, most of the compressions took place at the costo-clavicular space (91.3%); this greatly matched the studies done by Ersoy et al. and Raptis et al. [9, 19].
Multi-level compression in the same extremity was seen in one patient (1.7%), and it was of the venous type, the compression was at the costo-clavicular space in addition to the retro-pectoral space as detected by dynamic duplex scanning, and this was considered as an uncommon finding.
Combined arterial and venous compression was the second type of compression being seen in 8 patients (13.7%) and occurred at the costo-clavicular space (Figs. 3, 4, and 5) and this also went with the Demondion et al. and Ersoy et al. studies [4, 9].
Pure arterial compression without venous compression was seen only in one patient in this study (1.7%) and occurred in the scalene triangle where the artery and the vein are anatomically separated from each other, and only the arteries are located in the scalene triangle alongside the brachial plexus; this could explain why the arterial TOS was being observed in conjugation with NTOS in some cases; thus, pure arterial compression is considered as a rare type of TOS and usually associated with an underlying osseous abnormality; thus, its presence necessitates an X-ray examination; nevertheless, the distal arterial embolism is considered as a feature complication of the condition [20,21,22], and this was also manifested in the present study, where the only case of pure arterial compression was at the scalene triangle and was associated with a bony cervical rib and distal subclavian artery aneurysm; moreover, a distal arterial embolism to the ipsilateral radial artery was present as well (Fig. 7).
Complicated venous compression occurred in two forms, the first one was the ASVT and this was detectable in (5.1%) of patients (Fig. 8), and this could be attributed to the repeated strenuous and overhead activities with frequent vein crushing between the osseous structures, namely the first rib and the clavicle-inducing endothelial injuries promoting venous thrombosis, and this condition could be termed Paget-Schroetter syndrome or effort-induced thrombosis [2, 21]. Actually, the affected patients with thrombosis in our study gave histories of occupational and sport-related overhead activities. The second form was a persistent venous stenosis at the site of compression and this was seen in one patient (1.7%); this greatly matched Ersoy et al.  and could be due to either endothelial injury from repeated trauma by extrinsic compression or perivenular fibrosis and adhesions .
Actually, we need to clarify that the present study was a description of US findings among patients referred with a clinical presentation of VTOS, but the spectrum of radiological observations overestimated the prevalence of disease, since most had only positional compression as a radiological finding, but the vascular injury that might support the clinical diagnosis had been described as a complication of long standing compression but at the same time, it should be clear that, whatever the imaging modality used for assessment of positional compression, this overestimation can occur as the imaging modalities mainly assess the degree of diameter or cross area reduction of the vessel lumen on the provocative maneuvers [4, 10, 11, 19, 22].
However, it is important to know that the cornerstones of the VTOS diagnosis are the clinical aspects through the meticulous history taking and the physical examination, and the role of imaging is to confirm the clinical diagnosis, detection of the site, and the cause of vascular impingement; delineate the abnormal anatomical structures; and to help in the classification of the VTOS into an arterial, venous, or both types and finally in detection of the superadded complications .
Imaging of VTOS had been implemented by multiple diagnostic modalities including plain radiography, conventional angiography (arteriography and venography), CT, MRI, and sonography; plain radiography of the cervical spine and the chest was obtained symmetrically and usually used to exclude an osseous abnormality of the thoracic outlet region that might impinge the neurovascular structures; those could be an osseous cervical rib (Fig. 1), elongated transverse process of C7, exostosis, callus of old clavicular, or first rib fractures [4, 21].
Conventional angiography including the arteriography and venography was considered as an invasive modality that could display the extrinsic vascular compression at certain anatomical location and may give an idea about the collateral vessels that circumvent the obstruction level but definitely missing the depiction of the impinging structure; thus, it may be better replaced by the less invasive imaging modalities . Conventional angiography has an important role in the management of VTOS in cases of the ASVT through the catheter-directed thrombolysis therapy as a prior procedure for surgical decompression of the VTOS; moreover, the arteriography may be employed for angioplasty and/or stent deployment in cases of residual stenosis after surgical decompression of arterial TOS .
CT angiography (CTA)
CTA examination with the arms beside the body (neutral position) and then with arm elevation (abduction position), then a comparison of the images obtained with the neutral arm position to those obtained with the abduction arm position were done to detect the degree of vascular narrowing by the postural changes . CTA gives valuable vascular anatomical details in the assessment of VTOS; however, there are many limitations including technical aspects regarding the arm elevation that could be hindered by the CT tunnel (especially if more than 120°) , the supine position of the CT examination which may be associated with high false-negative results , and the CTA examination is done is associated with exposure to ionizing radiation as well as the side effects of contrast media.
MR imaging (MRI)
MRI and especially the magnetic resonance angiography (MRA) examinations are noninvasive, cross-sectional imaging modalities that have multiplanar capabilities with no exposure to ionizing radiation; they exhibit a better spatial and temporal resolution of the anatomical details; again, multiple positions are required for evaluation of the vascular narrowing with the postural changes. Certain planes are considered especially important like the sagittal planes in T1-weighted sequences as well as the coronal planes, and then the degree of the vascular compression is assessed by comparing the diameter reductions of the vessels in the arm abduction with that in the neutral position [4, 11, 19, 22].
Like CTA, the MRI has some limitations regarding the arm abduction as well as the supine position which is associated with high false-negative results as previously mentioned.
Raptis et al. described the use of contrast-enhanced MRI in VTOS with a special recommendation to the use of blood pool contrast agent (gadofosveset trisodium) in order to do a single injection for the two arm positions . Again, the use of the contrast agents is contraindicated in cases with renal impairment.
The relatively high cost of the MRI compared to the other modalities in addition to its contraindications like claustrophobia and metallic implants (like pacemakers) may limit its use in certain circumstances.
Thanks to its availability, simplicity, noninvasive nature as well as being inexpensive modality, the ultrasound had gained a wide popularity; moreover, there is no hazardous exposure to ionizing radiations or use of contrast material.
In contrast to CT and MRI, the duplex ultrasound can be done in the upright position, thus avoiding the high false-negative results associated with the supine position.
The dynamic duplex ultrasound gives the chance for a direct correlation between the dynamically provoked symptoms and the associated vascular compression at the same time. Additionally, the determination of the degree of arm abductions associated with symptoms could be easily done.
The postural induced hemodynamic changes like blunting of the arterial waveform, flow cessation, and high-velocity jets of stenosis could be easily performed by the dynamic duplex ultrasound.
The arteries and the veins of both upper extremities could be examined at the same session by dynamic duplex ultrasound.
Butros et al. had special consideration for the use of duplex ultrasound in the venous TOS which is to be limited for diagnosis of the associated venous thrombosis with a limited value in the detection of thrombosis that extended to the central veins in the thorax; in addition, they considered that its use in cases of venous TOS—in the absence of thrombosis—is still equivocal when compared to CT or MRI .
Raptis et al. preferred the use of the duplex ultrasound in the clinical setting to prove the patency of the vessels and to detect abnormalities like thrombosis, aneurysms, or pseudo-aneurysms but not to use it in exclusion of the venous TOS when there is a clinical suspicion; they justified this by the limited visualization of the central subclavian vein due to the acoustic shadow of the clavicle . We disagree with this point because the assessment of the compression of the veins took place at the axillary-subclavian vein junction which is present in the outlet of the costo-clavicular tunnel (distal to the lower edge of the clavicle); then, by the postural maneuvers, the compressed vein displayed a peak-like configuration with a tapering end toward the costo-clavicular tunnel outlet, and the associated color Doppler and spectral Doppler changes would be apparent just distal to this level, thus giving the chance for the assessment of the degree of vascular compression (Figs. 3, 4, and 5); moreover, the indirect signs like vein distension, flow cessation, and lack of the respiratory phasicity of the flow in the venous segment downstream, this compression level would be helpful.
Demondion et al. went for the use of ultrasound as a supplementary technique for the CT and the MRI in diagnosis of VTOS especially in cases that had positive clinical findings but the CT and the MRI findings were negative, they also explained this by the limitation of the ultrasound in detecting other pathologies that could affect the lung apex (like tumors) and might give a clinical picture mimicking the TOS .
As a general rule, it should always be kept in mind that the diagnosis of VTOS is clinically based, and the diagnosis could not be established based only on the vascular compression by any imaging modality; thus, the interpretation of the images should be done in parallelism with the clinical diagnosis [1, 3, 4, 19].
Longley et al. suggested the use of color Doppler ultrasound in the workup of cases with venous TOS as a promising technique through evaluation of the subclavian vein, but its use in cases of arterial TOS was still questionable in their limited study .
Literally, the imaging findings of vascular compression with postural changes may be detectable even in asymptomatic subjects; thus, the clinician and the radiologist should be aware of such bias so as not to do unnecessary surgical interventions .
We had an explanation for the absence of the symptoms in some individuals who might have imaging evidence of vascular compression; in fact, these individuals had a narrow space for passage of the neurovascular structures but actually the overuse and the repeated micro-trauma to the vessels may precipitate the symptoms especially on the long-run scales; this could be noticed in persons who had certain occupations and even gymnastics with overhead activities; moreover, some individuals might have unilateral symptoms in spite of the presence of bilateral vascular compression by the imaging but usually the symptoms were seen in the dominant side, then by a meticulous history taking some patients reported the presence of occasional symptoms in the asymptotic side but to a much lesser degree than the symptomatic side.
As we discussed, some authors suggested the use of the dynamic duplex for evaluation of the presence of the VTOS and put the criteria for the diagnosis [3, 4, 12, 24], and some limited its use for the clinical setting and for detection of complications or even as a supplementary modality when there are positive clinical findings and negative imaging findings by CT or MRI; in addition, it had proved usefulness in the follow-up assessment of the post-surgical decompression cases [1, 4, 19]. In our experience, the dynamic duplex examination is a good diagnostic modality for assessment of the vascular compression in VTOS and for detection of any superadded complications of vascular compression, unlike plain radiography and CT, it may be of limited use in the demonstration of the osseous abnormalities. Both dynamic duplex and the other noninvasive imaging modalities (CT or MRI) can reveal vascular compression in VTOS but the image interpretation and the planning for surgical interventions should be first done in the light of the clinical diagnosis for all modalities.
Considering the availability, cost-effectiveness, and noninvasive nature of the duplex ultrasound as well as the wide range of the postural changes given by dynamic duplex examination, this modality is warranted for assessment VTOS and might be complemented by other modalities like plain radiography, CT, or MRI if there is a clinical indication.
A novel ultrasound finding called wedge-sickle sign has been recently described in the identification of the fibromuscular bands that may exert a compression on the brachial plexus in the interscalene triangle, thus helping for establishing an early diagnosis before a neurologic deficit could supervene ; this sign had greatly helped for ultrasound diagnosis of cases with NTOS; however, this was not our main concern in the present study where we targeted the cases of VTOS.
Some limitations were met in this work; the first one was regarding the technique of examination, being deficient in demonstrating the osseous abnormalities like cervical ribs as well as the pulmonary apex region; however, it was further complemented by other modalities if there was a clinical indication; the second one, also, there was no reference imaging standard for the diagnosis (like catheter angiography, CTA, or MRA), apart from the clinical examination, and all the cases were diagnosed clinically, and the main imaging study was the dynamic duplex examination; thus, all other imaging studies were done upon the clinical need.