Indocyanine green: utility in benign hepatobiliary surgery

Indocyanine green (ICG) is a fluorescent dye that has been widely employed in different fields: for confirming the patency of vascular reconstruction surgery, anastomosis of the gastrointestinal tract, brain aneurysms, identification of sentinel lymph node, and it also plays an important role in fluorescence imaging during hepatobiliary surgery, in both malignant and benign pathologies.

ICG characteristics In the early 1970s, fluorescence imaging systems using ICG were introduced as an intra-operative method for retinal angiography. Since then, as mentioned before, its usage has been extended. When ICG is injected intravenously is selectively taken up by the liver, and then secreted into the bile. The catabolism and fluorescence properties of ICG permit a wide range of visualization methods in hepatobiliary surgery. ICG emits fluorescence when excited by infrared light. Light penetration depth is no larger than 10 mm (tissue optical window), which sometimes makes difficult to observe the fluorescence in obese patients or inflammatory situations. ICG binds to plasma proteins and lipoproteins to form aggregated dye molecules in physiological environments. Binding of ICG to plasma proteins does not alter protein structure, therefore intravenous administration of ICG is not toxic. The side effects reported with the use of ICG are seen in less than 1 out of 40,000 patients.

ICG fluorescence imaging in hepatobiliary surgery. – Liver mapping: During resection, all the liver segments should be clearly defined. For this purpose, intra-operative contrast-enhanced ultrasound remains the gold standard. However, portal hypertension caused by liver cirrhosis might obstruct conventional liver mapping by ultrasonography. Fluorescence imaging is a safe and sensitive method for identifying liver segments during liver resection, even in the case of liver cirrhosis. – Partial liver transplantation: ICG has been employed to visualize flow turbulence in reconstructed vessels and to evaluate patency, kinking, and stenosis of vascular anastomoses following partial liver transplantation. – Intra-operative fluorescence cholangiography: ICG cholangiography is an alternative to conventional cholangiography. It does not involve radiation. With intravenous ICG administration, the cystic duct can be identified without dissection of Calot’s triangle. It can be administered directly into the gallbladder as well, to identify the biliary tree anatomy.

ICG cholangiography during laparoscopic cholecystectomy. Laparoscopic cholecystectomy (LC) is one of the most common operations in the surgical field. Bile duct injury is rare, with an incidence of 0.3% to 0.7% but it can lead to serious consequences. Surgery for cholecystitis tends to be difficult, even for high-volume surgeons. An intraoperative cholangiography technique during laparoscopic cholecystectomy, involving the excretion of fluorescent ICG in the bile after intravenous injection has been used to determine the bile duct anatomy.

ICG cholangiography during laparoscopic cholecystectomy. One of the most significant drawbacks of cholangiography following systemic ICG injection lies in the very high background signal due to the rapid accumulation of ICG in the liver, which can impair the visualization of the biliary structures. Injecting ICG directly into the gallbladder could be a valid strategy to improve the visualization of the cystic duct and the common bile duct without suffering from the disturbing background liver enhancement.

ICG cholangiography during laparoscopic cholecystectomy. In case of severe inflammatory reaction (e.g cholecystitis), ICG cholangiography enabled a significantly better visualization of Hartmann’s pouch, of the common bile duct and of the common hepatic duct. However, in case of cystic duct occlusion because of stone impaction, the biliary tree could not be visualized by means of NIR imaging, after intragallbladder ICG injection, which makes it necessary to remove the stones. ICG cholangiography, either administered intravenously or directly into the gallbladder is a valuable tool to increase the safety of laparoscopic cholecystectomy.