Overview

Definition:
-Indocyanine Green (ICG) is a water-soluble, FDA-approved fluorescent dye that emits near-infrared (NIR) fluorescence when excited by light at specific wavelengths
-In surgery, ICG fluorescence imaging allows for real-time visualization of anatomical structures, physiological processes, and pathological lesions that are otherwise invisible to the naked eye.
Epidemiology: While not a disease entity, ICG fluorescence imaging is increasingly adopted across various surgical specialties, with its prevalence growing significantly in oncologic, hepatobiliary, gastrointestinal, and reconstructive surgery due to its safety profile and diagnostic capabilities.
Clinical Significance:
-ICG fluorescence enhances surgical precision by enabling real-time assessment of tissue perfusion, lymphatic drainage, and tumor margins
-This leads to improved operative outcomes, reduced complications, and better oncological control
-It is particularly valuable in complex reconstructive procedures and in identifying critical structures during minimally invasive surgery, making it highly relevant for DNB and NEET SS surgical examinations.

Principles Of Icg Fluorescence

Mechanism Of Action:
-ICG binds to plasma proteins and is rapidly taken up by hepatocytes and excreted into the biliary system
-It absorbs light in the visible spectrum (around 805 nm) and emits NIR fluorescence (peak emission around 835 nm), which can penetrate tissues deeper than visible light, allowing for non-invasive imaging.
Excitation And Emission:
-Excitation light, typically from a laser or LED source in the near-infrared spectrum, prompts ICG to fluoresce
-The emitted light is captured by specialized cameras, often integrated into surgical microscopes or laparoscopic systems.
Safety Profile:
-ICG has a very low toxicity profile with minimal allergic reactions reported (less than 0.1%)
-It is rapidly metabolized and excreted, posing little risk to patients
-This safety profile supports its widespread use across diverse surgical scenarios.

Surgical Applications

Lymph Node Mapping:
-ICG injected near a tumor site delineates lymphatic pathways, allowing for precise identification of sentinel lymph nodes (SLNs) in oncological procedures like breast cancer or melanoma surgery
-This guides lymphadenectomy and staging.
Tumor Visualization: In certain tumors (e.g., hepatocellular carcinoma, glioblastoma), ICG can accumulate or be preferentially taken up, aiding in the identification of tumor margins and enhancing complete resection rates during oncological surgery.
Biliary Tree And Ureteral Identification:
-ICG injected intravenously or into the biliary tree clearly visualizes the biliary anatomy and identifies potential fistulas or leaks
-Its fluorescence also highlights the ureters during pelvic surgery, preventing iatrogenic injury.
Vascular Assessment:
-ICG perfusion imaging assesses tissue viability and blood flow in flaps during reconstructive surgery or in organs like the bowel during anastomotic procedures
-It helps confirm adequate perfusion and identify areas of ischemia.
Gastric Emptying Studies: While more common in research, ICG can be used to assess gastric motility and emptying, providing insights into post-gastrectomy functional outcomes.

Icg Imaging Systems And Technique

Equipment:
-Modern surgical platforms (e.g., da Vinci systems, Olympus, Stryker) offer integrated fluorescence imaging capabilities
-Specialized handheld devices and microscopes are also available
-These systems typically comprise an excitation light source, a specialized camera, and software for image processing.
Administration Routes: ICG can be administered intravenously for systemic perfusion studies, peritumorally for lymphatic mapping, intraduodenally for cholangiography, or intra-articularly for joint imaging.
Timing And Interpretation:
-Optimal visualization timing varies depending on the application
-For SLN mapping, fluorescence appears within minutes, while for tumor visualization, it may take longer
-Accurate interpretation requires understanding the specific physiology and kinetics of ICG in each context.

Advantages And Limitations

Advantages:
-Real-time visualization
-enhanced anatomical identification
-improved surgical precision
-reduced risk of iatrogenic injury
-better oncological resection
-intraoperative decision support
-wide safety margin.
Limitations:
-Can be affected by overlying fat or scar tissue
-potential for false negatives or positives depending on technique and tumor biology
-requires specialized equipment
-learning curve for optimal interpretation
-cost of equipment.

Key Points

Exam Focus:
-Understand the principle of ICG fluorescence, its excitation and emission wavelengths, and common applications in surgery: SLN mapping, tumor visualization, biliary/ureteral identification, and vascular assessment
-Know the safety profile
-Be prepared for questions on timing of administration and interpretation.
Clinical Pearls:
-In laparoscopic surgery, the combination of near-infrared fluorescence with standard white light (e.g., Firefly® technology) offers synergistic visualization
-Always confirm unexpected fluorescence with anatomical knowledge or other methods
-Dilution and injection technique are crucial for successful SLN mapping.
Common Mistakes:
-Incorrect timing of ICG injection or imaging
-inadequate dose
-poor injection technique leading to diffuse staining
-misinterpreting lymphatic drainage patterns
-over-reliance on fluorescence without anatomical correlation.