The SpyGlass DS Direct Visualization System is a sterile and disposable device composed of a flexible catheter useable in a normal duodenoscope with a working channel. Compared to the previous version, an integrated digital sensor provides superior imaging, far greater resolution, and a 60 % wider field of view. The controller is an endoscopic video imaging system that combines the functionality of a camera and a LED light source. The controller receives video signals from the catheter, processes the video signals, and outputs video images to an attached monitor. It also generates and controls the illumination transmitted to the distal end of the catheter. The catheter comprises a control section, an insertion tube, and a connection cable. The control section is provided with a handle with two knobs that allow the orientation of the distal end of catheter in the four directions, with a minimum inclination of 30° in the presence of all accessories. Moreover, it owns a locking lever and a urethane band under the operator channel, which lock the system at the duodenoscope. The flexible catheter (SpyScope) consists of a Teflon device of 3.3 mm (10 Fr). It contains one working channel (1.2 mm) that allows the passage of dedicated biopsy forceps, probes for lithotripsy, or laser and guide wires, two channels (0.6 mm) for irrigation, two optical fibers to transmit illumination from the controller, and wiring to transmit video signals to the controller. The catheter is introduced through a duodenoscope that has an operating channel of at least 4.2 mm² (Figs. 12.1 and 12.2).

The biopsy forceps (SpyBite) are sterile and disposable accessories for sampling intraductal biopsy. They have an external diameter of 1 mm and a length of 286 cm, with an opening of 4.1 mm. The irrigation system consists of a sterile tube set connected to an irrigation pump, activated with a pedal.

There are different indications for SOC-S use. It can be used for diagnostic and therapeutic procedures. Among common uses, there are difficult biliary stones and macroscopic and histological typing of indeterminate biliary strictures. Less common uses are the selective guide wire placement in a bile duct, the evaluation of either stenosis after a liver transplant or filling defects of the bile ducts not characterized by other methods (MRI, ERCP, EUS), as well as resolution of multiple lithiasis. The rare uses comprise staging or endoscopic ablation of tumors, the trans-papillary gallbladder drainage, and evaluation of hemobilia.

Intraductal lithotripsy is the main therapeutic application of SOC-S when conventional procedures fail. The failure rate in the treatment of choledocholithiasis following standard endoscopic retrograde cholangiopancreatography (ERCP) is ranging between 8 and 16 % [8, 9]. A partial bile duct clearance depends on stones’ characteristics (number, size, shape, texture, seat), the bile duct structure (shape, size, low insertion of the cystic duct), and the presence of a juxtapapillary diverticulum. Common bile duct and Wirsung lithiasis can be treated with laser (LL) or electrohydraulic lithotripsy (EHL). In such a field, the SOC-S has two important advantages. The first is to allow a direct visualization of the lumen and the stones position, avoiding duct damage. The second is to consent the correct functioning of the EHL device through the irrigation of bile ducts with the saline solution. In fact, the 1.9 Fr nitinol catheter of the EHL presents two insulated coaxial electrodes in the tip that produce sparks generating high-amplitude hydraulic pressure waves able to fragment the stones [10, 11]. The LL fragments stones using a laser beam that is delivered by means of a quartz flexible fiber introduced in the SOC-S operator channel. The pulsed application of the beam generates ion formations and free electrons at high energy with consequent spherical mechanical waves which fragment the stones [12]. A complete common bile duct drainage was achieved in 92 % of 26 patients with difficult cholelithiasis who failed three ERCP sessions with standard mechanical lithotripsy [13]. Similarly, following a mean of 1.2 sessions, a 100 % common bile duct clearance was reported by using Holmium laser lithotripsy in 60 patients with mechanical lithotripsy failure (stones average size of 23 mm), or with other conditions, such as the Mirizzi syndrome or stone impacted [14]. In a recent retrospective single-center study, a 77 % technical success in removing gallstones from the bile duct was reported [15].

The SOC-S has been used in 13 patients with cystic duct stones, including four with Mirizzi syndrome type 1, achieving complete clearance of both cystic duct and common bile duct in 77 % of cases [16]. In a prospective, multicenter study, 66 patients with difficult biliary stones (stones average size of 19 mm) underwent EHL (50 cases) or LL (16 cases). A complete bile ducts’ clearance was achieved in all cases, with two sessions being needed in only 29 % of cases [17]. A case report showed a successful biliary lithiasis treatment with SOC-S and EHL by using an operator colonoscope in a patient with hepatic jejunostomy with Roux-en-Y reconstruction [18]. Of note, the use of SOC-S in pregnant women with gallstones allows to prevent radiological exposure [19]. Finally, a percentage of missed stones ranging between 8 and 30 % should be also taken into account, including those small stones not visible after contrast medium or masked by larger stones. These could be diagnosed and successfully treated by using the SOC-S [20, 21]^.

Pancreatic lithiasis is a demanding challenge for the endoscopist. Although there are only preliminary data, pancreatic lithiasis represents another promising therapeutic application of SOC-S. The efficacy of peroral pancreatoscopy with endoscope and that of SOC has been compared in series of 45 patients with main pancreatic duct (MPD) lithiasis [22]. A complete or partial clearance was obtained in 57 % and 100 % of case, respectively, without a difference between the two tools. In three patients (12 %) treated with SpyGlass, minor complications related to pancreatoscopy occurred. In a US multicenter, retrospective study on the efficacy of SOC-S in the treatment of the MPD lithiasis in 28 patients undergoing pancreatoscopy with LL was described [23]. The average size of stones was 15 mm (range: 4–32 mm). The stone removal was successful in 79 % of cases, with a partial clearance in further three (11 %) patients. Moreover, there was a good clinical outcome in 89 % of cases at 1 year follow-up, in terms of pain reduction, use of narcotics, and hospitalization. Recently, the use of SpyGlass-guided EHL was found to be a valid alternative for pancreatic lithiasis treatment in 98 patients following a failure of combined endoscopic lithotomy and extracorporeal shock wave lithotripsy (ESWL) [24].

The ability to discriminate between benign and malignant biliary strictures is obviously of crucial importance in patient care management. The current radiologic methods (CT, MRI) do not provide adequate sensitive and specific diagnostic performance for all biliary-pancreatic lesions. The cytological sampling by brushing during ERCP or fine-needle aspiration (FNA) during endoscopic ultrasonography showed high specificity but modest sensitivity [25, 26]. Disappointing results were achieved even by using more performing brushes, dilation of stenosis before brushing, or gene analysis of the collected tissue [27]. Several cohort series on the use of SOC-S in this field showed encouraging results [7]. However, the macroscopic characteristics of malignant biliary lesions are not completely standardized. Some studies on cholangioscopy with endoscope or SOC have defined highly suggestive criteria. They include the presence of dilated and tortuous vessels (“tumor vessel sign” or “capillary signs”), ulceration, nodules, exophytic or papillary excrescences, friability, and irregular surface [9, 28, 29]. On the other hand, mucosal alterations with a smooth surface or finely granular without neovascularization or intraductal masses suggest a benign condition [30]. A 61 % sensitivity and a 100 % specificity, with a 100 % interobserver agreement, for tumor vessel sign were found in a study [31]. On the contrary, another study found a good interobserver agreement with SOC only for tumoral masses, strictures, ulceration, and hyperplasia, stressing the need of validating the cholangioscopic criteria for biliary lesions [32]. When a suspected lesion is encountered, biopsies with SOC-S can be obtained by following two procedures: (1) cholangioscopy-direct biopsy obtained with the dedicated mini-forceps (SpyBite, Boston Scientific) and (2) cholangioscopy-assisted biopsy, which consists in identifying fluoroscopically the stricture area, to withdraw the cholangioscope, and to insert a standard forceps, until the stenosis under fluoroscopic guide [28]. Of note, by using the SpyBite, an adequate quantity of tissue was obtained in more than 95 % of cases [9, 13]. A prospective study involving 26 patients with indeterminate biliary strictures found that sensitivity, specificity, and accuracy of biopsies obtained with SpyBite were significantly higher as compared to either cytology or standard biopsy under fluoroscopic guidance [33]. In our experience, sampling performed with SpyBite was adequate in 97.5 % of 45 patients, with a sensitivity, specificity, and positive and negative predictive values of 93 %, 88 %, 87 %, and 94 %, respectively [34]. Another study found a 92.3 % and 74.4 % technical and clinical success, respectively, on 39 patients with indeterminate biliary strictures, and PPV and NPV as high as 100 % and 95.8 % [15]^.