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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.
