Endovascular stenting has been used for seventeen years for the treatment of NCS due to its minimally invasive nature. A survey of the published English literature revealed 124 cases treated in this manner including our largest stenting experiences to date [2]–[9]. Although, the current literature suggests that stenting is a safe and effective procedure, stent migration notes in 7.3 % of all cases [2]–[5]. The reason of endovascular stent migration may be the effect of cardiac motion, early activity, mismatch between renal vein diameter or stent diameter, or inaccurate positioning of the stent within the lesion.

The clinical implications of migration are significant and can lead to thrombosis, vessel trauma, embolization, and its most disastrous consequence (rupture). It requires prompt and effective diagnosis and management to prevent potentially implications.

Sequence of image for diagnosis or follow-up has more or less been rationalized to duplex ultrasound, computerized tomography or magnetic resonance angiography, and finally left renal venography [2]. Duplex ultrasound is the easiest and the least expensive method. Zhelan Zheng et al. [10] pointed out standards for ultrasonic diagnosis of the disease as follows: (1)the low velocity of stenosis of the LRV at supine position accelerates remarkably, and the acceleration is more obvious after standing for 15 min,which is more than 100 cm/s; (2) the inner diameter ratio between renal hilum and stenosis of the LRV at supine position is more than 3, while it is more than 5 after standing for 15 min. When two index are coincident with the standards, NCS may be primary diagnosed. The CTA (including non-invasive 3-D) may be a useful tool in the diagnosis of the NCS and follow-up testing. CTA provided fine outlines that gave a precise depiction of both endovascular stent migration on the left of the SMA and a compression of the LRV between the aorta and the SMA. Furthermore, the stent migrating distance can be measured, and many distorting collateral veins were seen arising from the LRV in the CTA. The CTA imaging was closely correlated to therapeutic interventions and stent migration.

The typical treatment is percutaneous removal of the migrated stent. However, under certain circumstances, such as stent migration to the heart, special stent, or endothelialization of stent, percutaneous removal may be difficult or even impossible, thus surgery may be required. Hartung et al. described a LRV stent that migrated into the retro hepatic inferior vena cava; an attempt to retrieve it with a Goose Neck failed when the stent took a transversal orientation after 5 cm, and further attempts also failed [4]. A patient with a nitinol stent is difficult to manage percutaneously because of its inherent characteristics and probable endothelialization of the stent in 1 year, which makes the procedure more challenging [11]. In our previous case, one stent migrated into the right atrium and the patient required surgery after unsuccessful percutaneous removal [3]. In such cases, surgical removal is a safer and more feasible option. However, surgical removal is associated with high morbidity: Long period of renal congestion and additional anastomoses. Compared with surgical removal, extravascular stenting is a minimally invasive treatment modality.

Compared with vascular displacement, extravascular stenting for NCS is a minimally invasive treatment modality. Especially for children and adolescents, intravascular stenting should be cautiously recommended because the lumen of the LRV may become wider and the stents cannot match any longer during physical development. One may postulate that externally suturing stent could be a way to keep it in place; therefore, Barnes firstly reported extravascular stenting and externally suturing the stent performed by open surgery in 1988 [12]. Currently, sporadic cases of extravascular stenting for the NCS have been reported with excellent outcome at short-term follow up [13]–[17]. The stent has good conformability to adapt to the vessel wall and adhere to the vessel wall tightly [6]. In our opinion, the extravascular approach to treat endovascular stent migration is favored to avoid the potential complications.

Consideration must also be given to the original stent placement. If removal is not possible or failed, the original stent should be fixed to prevent repeated movements of the stent. Both the new and old stents should be sewn to the vessel wall to ensure that the extravascular and endovascular stents did not migrate, as shown in our case.

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Endovascular stenting has been used for seventeen years for the treatment of NCS due to its minimally invasive nature. A survey of the published English literature revealed 124 cases treated in this manner including our largest stenting experiences to date [2]–[9]. Although, the current literature suggests that stenting is a safe and effective procedure, stent migration notes in 7.3 % of all cases [2]–[5]. The reason of endovascular stent migration may be the effect of cardiac motion, early activity, mismatch between renal vein diameter or stent diameter, or inaccurate positioning of the stent within the lesion.

The clinical implications of migration are significant and can lead to thrombosis, vessel trauma, embolization, and its most disastrous consequence (rupture). It requires prompt and effective diagnosis and management to prevent potentially implications.

Sequence of image for diagnosis or follow-up has more or less been rationalized to duplex ultrasound, computerized tomography or magnetic resonance angiography, and finally left renal venography [2]. Duplex ultrasound is the easiest and the least expensive method. Zhelan Zheng et al. [10] pointed out standards for ultrasonic diagnosis of the disease as follows: (1)the low velocity of stenosis of the LRV at supine position accelerates remarkably, and the acceleration is more obvious after standing for 15 min,which is more than 100 cm/s; (2) the inner diameter ratio between renal hilum and stenosis of the LRV at supine position is more than 3, while it is more than 5 after standing for 15 min. When two index are coincident with the standards, NCS may be primary diagnosed. The CTA (including non-invasive 3-D) may be a useful tool in the diagnosis of the NCS and follow-up testing. CTA provided fine outlines that gave a precise depiction of both endovascular stent migration on the left of the SMA and a compression of the LRV between the aorta and the SMA. Furthermore, the stent migrating distance can be measured, and many distorting collateral veins were seen arising from the LRV in the CTA. The CTA imaging was closely correlated to therapeutic interventions and stent migration.

The typical treatment is percutaneous removal of the migrated stent. However, under certain circumstances, such as stent migration to the heart, special stent, or endothelialization of stent, percutaneous removal may be difficult or even impossible, thus surgery may be required. Hartung et al. described a LRV stent that migrated into the retro hepatic inferior vena cava; an attempt to retrieve it with a Goose Neck failed when the stent took a transversal orientation after 5 cm, and further attempts also failed [4]. A patient with a nitinol stent is difficult to manage percutaneously because of its inherent characteristics and probable endothelialization of the stent in 1 year, which makes the procedure more challenging [11]. In our previous case, one stent migrated into the right atrium and the patient required surgery after unsuccessful percutaneous removal [3]. In such cases, surgical removal is a safer and more feasible option. However, surgical removal is associated with high morbidity: Long period of renal congestion and additional anastomoses. Compared with surgical removal, extravascular stenting is a minimally invasive treatment modality.

Compared with vascular displacement, extravascular stenting for NCS is a minimally invasive treatment modality. Especially for children and adolescents, intravascular stenting should be cautiously recommended because the lumen of the LRV may become wider and the stents cannot match any longer during physical development. One may postulate that externally suturing stent could be a way to keep it in place; therefore, Barnes firstly reported extravascular stenting and externally suturing the stent performed by open surgery in 1988 [12]. Currently, sporadic cases of extravascular stenting for the NCS have been reported with excellent outcome at short-term follow up [13]–[17]. The stent has good conformability to adapt to the vessel wall and adhere to the vessel wall tightly [6]. In our opinion, the extravascular approach to treat endovascular stent migration is favored to avoid the potential complications.

Consideration must also be given to the original stent placement. If removal is not possible or failed, the original stent should be fixed to prevent repeated movements of the stent. Both the new and old stents should be sewn to the vessel wall to ensure that the extravascular and endovascular stents did not migrate, as shown in our case.

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