Overview
Definition:
Sentinel node biopsy (SNB) is a surgical procedure to identify and remove the first lymph node(s) that drain fluid from a primary tumor site
Indocyanine green (ICG) fluorescence mapping is an advanced technique that utilizes near-infrared fluorescence to visualize lymphatic pathways and pinpoint sentinel nodes, enhancing accuracy and potentially reducing false negatives in staging cancer metastasis.
Epidemiology:
SNB is standard of care in early-stage melanoma and breast cancer
Its application is expanding to vulvar cancer, penile cancer, and other solid tumors
The incidence of positive sentinel nodes varies by primary tumor type, stage, and patient factors, directly influencing treatment decisions and prognosis.
Clinical Significance:
Accurate staging of regional lymph nodes is crucial for determining prognosis and guiding adjuvant therapy
SNB with ICG mapping improves sentinel node identification rates compared to traditional methods like blue dye or radioactive tracers, leading to more precise staging, reduced rates of lymphedema from unnecessary axillary dissection, and improved oncological outcomes.
Indications
Tumor Types:
Melanoma (thin/intermediate depth), Breast Cancer (clinically node-negative T1-T3N0), Vulvar Cancer (stage I-II), Penile Cancer (clinical node-negative)
Consideration for other malignancies with lymphatic drainage patterns.
Patient Factors:
Clinically negative axilla/groin for breast/vulvar/penile cancers
Absence of prior nodal surgery or radiation at the drainage site
Generally, patients with cN0 disease.
Contraindications:
Advanced nodal disease (cN+), previous lymphatic surgery or radiation to the draining basin, known allergy to ICG (rare), inability to tolerate surgical procedure
Extensive tumor involvement of lymphatic channels.
Preoperative Preparation
Patient Counseling:
Discuss procedure, risks, benefits, alternatives, and expected outcomes
Informed consent is paramount
Explain the role of ICG fluorescence and its safety profile.
Imaging And Staging:
Confirm initial staging with appropriate imaging (e.g., ultrasound, CT, MRI, PET-CT) to rule out overt nodal metastasis
Thorough clinical examination of nodal basins.
Icg Preparation:
Ensure sterile preparation of ICG solution (typically 2.5 mg/mL or 1.25 mg/mL)
Confirm availability of near-infrared fluorescence imaging system (e.g., SPY Elite, Photodynamic Eye) and sterile consumables.
Anesthesia And Prophylaxis:
General or regional anesthesia as appropriate
Prophylactic antibiotics may be administered based on institutional protocols and procedure type
Preoperative imaging review with the surgical team.
Procedure Steps
Icg Injection:
Subareolar, peritumoral, or subdermal injection of ICG solution(s) around the primary tumor site or directly into tumor bed (if excised prior)
Multiple injection sites may be used for complex lymphatic drainage
Timing of injection relative to incision is critical.
Lymphatic Mapping:
Allow 5-10 minutes for ICG to perfuse lymphatic channels
Using the near-infrared fluorescence imaging system, visualize the lymphatic vessels draining from the injection site and identify the glowing sentinel lymph nodes.
Sentinel Node Identification And Excision:
Make a minimal incision over the intensely fluorescent node(s)
Carefully dissect the sentinel node(s), preserving surrounding tissue
Confirm fluorescence with the imaging system before complete excision
Multiple sentinel nodes may be identified and excised.
Confirmation And Closure:
Document findings, including number of nodes identified and excised
If intraoperative frozen section is performed, proceed accordingly
Close incision in layers, ensuring hemostasis
Post-excision confirmation of lymphatic drainage pathway visualization is optional.
Postoperative Care
Wound Care:
Standard surgical wound care
Monitor for signs of infection, seroma, or hematoma
Dressings to be kept clean and dry.
Pain Management:
Analgesics as needed for incisional pain
Multimodal pain management strategies may be employed.
Monitoring For Complications:
Observe for signs of lymphedema, wound complications (dehiscence, infection), persistent pain, or sensory changes
Patient education on recognizing and reporting these symptoms.
Pathology Reporting:
Submit sentinel nodes for histopathological examination, including hematoxylin and eosin (H&E) staining and immunohistochemistry (e.g., cytokeratin) for micrometastases, as per established guidelines
Report of the number of sentinel nodes identified and examined, and the presence and extent of metastasis.
Complications
Early Complications:
Wound infection
Seroma or hematoma formation
Persistent pain or paresthesia at incision site
Transient skin staining at injection site.
Late Complications:
Lymphedema (reduced risk compared to full dissection)
Lymphocele
Chronic pain
Scarring
False negative biopsy leading to understaging and inadequate adjuvant therapy.
Prevention Strategies:
Meticulous surgical technique
Adequate hemostasis
Appropriate wound closure
Patient education on recognizing and reporting symptoms of complications
Careful adherence to injection and mapping protocols to maximize sentinel node yield and minimize false negatives.
Key Points
Exam Focus:
ICG fluorescence enhances sentinel node visualization, improving identification rates and reducing false negatives
Key indications are melanoma and breast cancer
Potential for false negatives due to lymphatic variations or technical errors.
Clinical Pearls:
Adequate time for ICG perfusion is crucial (5-10 mins)
Multiple injection sites may be necessary
Intraoperative imaging system proficiency is vital
Careful dissection to avoid damaging the lymphatic channels before node identification.
Common Mistakes:
Insufficient ICG dose or delayed imaging
Inadequate injection technique
Poor visualization due to ambient light interference
Failure to identify all sentinel nodes
Over-reliance on single method without considering alternatives like radioactive tracers if available.