The biliary system includes the gallbladder, liver and pancreas, and forms an essential part of the body's digestive system. Its primary function is to aid digestion and elimination of the body's waste through the controlled release of bile into the duodenum. Bile is released through a network of tube‑like structures called the biliary ducts.

Various disorders can result in narrowing or obstruction of the biliary ducts. The most common are as follows (Hoad‑Robson 2013):

  • Bile or pancreatic duct stones: approximately 15% of the adult population are thought to have gallstone disease (for more information, see the NICE guideline on gallstone disease). Benign or malignant tumours: pancreatic cancer has an incidence rate of 139 cases per million population (Cancer Research UK 2014).

  • Pancreatitis (inflammation of the pancreas): incidence of acute pancreatitis in the UK ranges from 150 to 420 cases per million population (Toh et al. 2000).

  • Primary sclerosing cholangitis (inflammation of the bile ducts), which has an incidence rate of 30 to 48 cases per million population (Card et al. 2008).

Endoscopic retrograde cholangiopancreatography (ERCP) is a procedure used to identify abnormalities in the biliary system. ERCP is done under X‑ray guidance using a duodenoscope (an endoscope designed for examination of the duodenum), which is inserted through the mouth of the patient after they have been sedated. Contrast medium (dye that shows up on X‑ray) is injected through the endoscope to outline the bile, pancreatic and liver ducts so that they can be examined. ERCP is used both to diagnose the narrowing of the biliary ducts and as a procedure to treat the underlying cause. The latter can involve the insertion of a stent (a small mesh tube) to widen a narrowed duct or fragmentation and removal of stones (lithotripsy).

There are 3 main lithotripsy techniques to break up bile or pancreatic duct stones: mechanical, electrohydraulic and laser. Mechanical lithotripsy is done using a metal‑wire basket, used to catch stones. The basket wires are then tightened, which crushes the stones into smaller fragments for removal. In electrohydraulic and laser lithotripsy, a shock wave is delivered directly to the stone (generated by a high voltage spark or a laser beam respectively). The clinician needs to be able to clearly see the biliary ducts when using these lithotripsy techniques in order to avoid damage to the surrounding tissues (Heller 2013).

Approximately 48,000 ERCPs are performed each year in the UK (Green et al. 2007). However, the procedure has limitations, mainly that it cannot provide direct visualisation of the ducts. This is important in cases where the cause of biliary strictures is not known, cases where the distinction between malignant and benign tumours is problematic, and in cases where there are large, difficult to remove stones which may need electrohydraulic or laser lithotripsy.

In cases where direct visualisation of the ducts is necessary, a technique called cholangioscopy is used. To perform standard cholangioscopy, a small‑calibre (less than 4.5 mm) endoscope (referred to as the 'baby' endoscope) is inserted through the working channel of a standard ERCP scope (referred to as the 'mother' endoscope) and into the biliary ducts. For a standard 'mother‑baby' cholangioscopy such as this, 2 endoscopists are needed: 1 to operate the duodenoscope and the other to operate the cholangioscope. Limitations of the procedure include the fragility of the 'baby' scope, its high repair cost, the requirement for 2 endoscopists to be present, and the limited tip deflection which reduces the range of visualisation.

The SpyGlass system is designed to overcome some of the limitations of the 'mother‑baby' technique to improve access to the biliary system and reduce the associated costs.