Magnets in action: role of interventional radiologists in magnetic compression anastomosis procedures

The majority of literature regarding MCA primarily focuses on biliary obstructions. Liver transplant recipients, in particular, suffer from biliary complications and impassable obstructions are not uncommon [19, 20]. In addition, iatrogenic injury of the biliary system during cholecystectomy may result in significant biliary stenosis and complete biliary obstruction in case of clipped bile duct [21]. MCA can be applied to both native and transplanted livers, however, rigorous assessment of the obstruction is essential for technical success. Endoscopy plays a more crucial role in the MCA of hepatobiliary obstructions compared to esophageal and ureteric obstructions. Retrograde catheterization of the cystic duct and afferent loop are essential steps of the procedure in the case of the clipped aberrant bile duct and Roux-en-Y hepaticojejunostomy, respectively.

MCA in the management of biliary obstruction encountered in native livers is relatively rare compared to transplanted livers. Post-surgical bilioenteric anastomosis strictures and traumatic injuries account for the majority of cases. Percutaneous biliary interventions are the initially preferred treatment options for bilioenteric anastomosis strictures because endoscopic retrograde cholangiopancreatography (ERCP) is challenging in this patient population due to altered anatomy, like in Roux-en-Y hepaticojejunostomy. In the presence of impassable biliary obstructions in these patients, MCA is challenging due to the limitations of ERCP. However, using a long endoscope (colonoscope or enteroscope) may enable access to the stricture site through the afferent loop, even in Roux-en-Y reconstructions [22, 23]. Although ERCP access may not be adequate for stent insertion or further interventions, MCA can still be achieved if a guidewire to carry one of the magnets can be advanced to the stricture site with the access obtained with the colonoscope (Figs. 1 and 2).

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Bile duct injury during cholecystectomy may also result in complete biliary obstruction due to clipped bile duct, particularly in patients with biliary anatomical variations [21]. Several types of biliary duct variations have been identified and right accessory biliary duct variations are held responsible for the majority of cases of bile duct injury during laparoscopic cholecystectomy [21, 24]. Ligation or clipping of aberrant right biliary truncus during cystic duct ligation in these patients results in isolated accessory biliary obstruction due to hampered bile drainage from these ducts to the main bile duct. MCA between the remaining part of the right accessory biliary truncus and the cystic duct may establish restored bile flow (Fig. 3). In addition, direct iatrogenic injury to the common bile duct may result in complete obstruction if left untreated (Fig. 4). The treatment commonly ends up with hepaticojejunostomy if the injury is detected during surgery. However, it may be diagnosed in the post-surgical period, and in this setting, rapid intervention should be performed because injury may result in retraction of the bile ducts which can preclude MCA.

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Several risk factors are held responsible for biliary complications following transplant surgery. Small and multiple anastomoses in patients with living donor transplantation, post-surgical adhesions/inflammation may result in biliary anastomosis stricture, and hepatic artery-related complications (i.e., decreased arterial blood supply or occlusion) may worsen the degree of stricture. In addition, the presence of a bile leak may result in biliary anastomotic stricture which may rapidly evolve to complete obstruction. Biliary strictures following liver transplantation can be encountered as anastomotic or non-anastomotic strictures. Anastomotic strictures are more common and more manageable with percutaneous and endoscopic procedures. Non-anastomotic strictures may occur due to various etiologies and have poorer prognosis. Management may vary depending on the type of anastomosis which can be performed as duct to duct [common biliary duct (CBD) of the donor to CBD of recipient] or hepatico/choledecho-jejunostomy or anastomosis of donor CBD to recipient’s cystic duct [4]. Most biliary anastomotic strictures are managed with endoscopic procedures. Percutaneous biliary interventions are reserved for failed ERCP cases or patients with hepaticojejunostomy anastomosis. Impassable complete biliary obstructions are not uncommon in liver transplant recipients. MCA may prevent risks of revision surgery, which is the conventional treatment option in these patients (Fig. 5).

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Recently published literature has revealed the success of MCA in ureteric obstructions [2, 12, 25]. Although the majority of ureteral obstructions can be traversed with guidewires, impassable strictures can be encountered. In contrast to biliary occlusions, endoscopic guidance is generally not required in the management of ureteral obstructions with MCA. With the latest technical improvements, the distal ureter can be catheterized under imaging guidance with only a few steps using several elemental tools [26]. One issue that should be addressed regarding the MCA of urinary obstruction is infection related to long-standing nephrostomy catheters. It may be encountered in hepatobiliary obstructions to some extent, however, it is not expected to be encountered in MCA of gastrointestinal obstruction due to a lack of drainage catheters.

Radiotherapy in the treatment of gynecological malignancies may result in significantly narrowed ureters [27, 28]. Care should be taken during the catheterization of ureteral strictures because ureteral integrity can be disrupted during guidewire insertion and the procedure may end up creating a false lumen and associated total ureteral occlusion. Once the false lumen is formed, it may be challenging to find the true lumen beyond the stricture (Fig. 6). Ureterovaginal fistula (UVF) is also another unfortunate complication encountered during the follow-up of patients who have undergone gynecological surgery and/or radiotherapy [27‐31]. Surgical treatment is usually avoided preferring less invasive treatment options such as imaging or cystoscopically guided procedures [29‐31]. Time of diagnosis is crucial in the treatment of ureterovaginal fistulae. Once a fistula is identified, interventions should be carried out as soon as possible to preclude fistula maturation [29‐31]. In the chronic state, any wire access beyond the fistula will probably fail to establish urinary diversion. However, MCA may restore the connection between the bladder trigone and the caudal part of the ureter even in chronic UVFs (Fig. 7).

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Cystectomy with ileal conduit is a type of surgery performed for patients with bladder cancer. The ureters are anastomosed to a reconstructed bladder which is placed at lower abdominal quadrants. The presence of inflammation and/or urinary leak, surgical challenges, and errors are held responsible for ileoureteral anastomosis strictures. These strictures can be traversed with antegrade or retrograde access gained with a nephrostomy or existing ostomy, respectively [32, 33]. During catheterization of the ileoureteral anastomosis stricture, care should be given to prevent extravasation which may result in distraction of the ureter from the anastomosis. In this case, patients may end up with permanent nephrostomy. Surgery is generally avoided in ileoureteral anastomotic obstructions, and interventional radiologists play a crucial role in the management of these obstructions [2, 32, 33]. Ileal pouch with an existing ostomy enables insertion of larger-sized magnets compared to native ureters, and therefore, more severe strictures may be treated with MCA due to enhanced attraction capacity with larger magnets (Fig. 8). MCA has also been reported as an effective procedure in renal transplant recipients with total ureteral obstructions [12].

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Esophageal obstructions are encountered following treatment of head and neck cancers and esophageal atresia, in adult and pediatric patient populations, respectively. Esophageal strictures are frequently managed with bougie and balloon dilation or stenting if wire access through the stricture can be established. However, in case of failure, surgical resection and reconstruction may be required which is a complicated procedure considering patient performance status and surgical challenges. MCA in the management of gastrointestinal obstruction has been reported even in pediatric patient populations [7‐9]. The procedure is similar to the above-mentioned obstructions. In patients with esophageal obstruction, a gastrostomy tube is inserted for enteral nutrition also enabling access to the caudal part of esophageal obstruction. The access to the cranial part of esophageal obstruction is more straightforward with the use of endoscopy or fluoroscopy-guided wire access. Various types of esophageal obstruction including esophageal atresia, post-surgical complication, or RT-induced obstruction can be treated with MCA (Fig. 9).

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MCA has been reported to be a safe and effective treatment option for small and large intestinal obstructions, as well [6, 13, 34]. Gastrojejunostomy can be reconstructed with MCA in patients with periampullary region tumors to enable oral nutrition [6, 13, 14]. Duodenal stent placement may not remain patent or overcome the obstruction in case of long-segment involvement. Therefore, these patients may undergo endoscopic ultrasound-guided gastrojejunostomy or surgical gastrojejunostomy which has its own disadvantages and challenges. However, several studies have demonstrated that MCA can be successfully performed to create an anastomosis between the stomach and jejunum, two different jejunal segments, or colonic segments in a minimally invasive manner [5, 6, 13, 34, 35]. However, the placement of a metallic stent following MCA in small intestinal obstructions remains controversial [6, 13, 14]. It should be noted that premature dilatation of MCA between gastrointestinal segments may result in perforation, which may end up with severe comorbidity and even death. Therefore, in the setting of gastrointestinal system MCA, any attempt to wire access beyond the obstruction should be delayed until magnets demonstrate spontaneous fall (Fig. 10).

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Impassable colonic obstructions are relatively rare, however can be encountered following surgery and radiotherapy. MCA can be preferred in these patients due to its minimally invasive nature, because of previous surgical procedures or history of radiotherapy that may challenge revision surgery. In colonic obstructions, MCA can be performed with magnets inserted through the anus and an existing enterostomy (Fig. 10).

The most important step in MCA is appropriate patient selection. Long segment obstructions may result in technical failure and procedural complications during magnet removal. The length of stricture is best evaluated when both cranial and caudal wire accesses to the stricture site are obtained. Once the wire accesses are established, magnets are pushed over the wires to the stricture site (supplementary video). Following magnet placement, daily radiographs should be obtained to evaluate magnet apposition. As mentioned above, in MCA of the gastrointestinal system, magnets are expected to demonstrate spontaneous fall following complete adherence, therefore any attempt that could be complicated with perforation should be delayed until spontaneous magnet fall. However, in the setting of biliary and urinary obstructions, an attempt to wire access beyond the obstruction can be performed following complete magnetic adherence on a plain radiograph.

Cross-sectional images frequently fail to demonstrate the correct distance of the stricture. In case of failure, magnets placed in the distal main bile duct or rectum will probably not raise trouble; however, magnets left within the intrahepatic bile duct, esophagus, or urinary system should be removed in case of failure of magnet adherence. A modified 10 F nelaton catheter carrying one fixed magnet at the tip can be advanced over a guidewire and used to grab and remove magnets under fluoroscopy (Fig. 11).

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The magnets placed at the obstruction should be in the correct direction before placement, therefore, before pushing magnets the attraction sites should be determined ex vivo. If magnets face each other with opposite sides, they push each other apart. In this case, a guiding catheter with an angled tip can be used to turn and/or push the magnets once again [2]. Last, in the presence of extravasation and loss of bile duct/ureteral/intestinal integrity, the procedure should be delayed to prevent the magnet fall into the abdominal cavity.