Overview
Definition:
Sentinel Lymph Node Biopsy (SLNB) is a minimally invasive surgical procedure used to identify and remove the first lymph node(s) that drain a primary tumor site
These are termed "sentinel nodes" as they are most likely to contain metastatic cancer cells if the cancer has spread from the primary tumor
The use of a radiotracer, typically Technetium-99m sulfur colloid, enhances the accuracy of sentinel node identification by allowing visualization with a gamma probe during surgery.
Epidemiology:
SLNB is predominantly used in the management of early-stage breast cancer and melanoma, where lymph node status is a critical prognostic factor
Its application is expanding to other malignancies like vulvar cancer, penile cancer, and gastric cancer
Accurate staging of lymph nodes significantly impacts treatment decisions, including the extent of lymphadenectomy and the need for adjuvant therapy.
Clinical Significance:
SLNB has revolutionized the staging of regional lymph nodes
By selectively removing sentinel nodes, it can accurately determine lymph node involvement, thereby avoiding unnecessary axillary lymph node dissection (ALND) in node-negative patients
This reduces the morbidity associated with ALND, such as lymphedema, pain, and impaired shoulder function, while maintaining accurate staging crucial for patient prognosis and management.
Indications
Breast Cancer:
Clinically node-negative (cN0) patients with invasive breast cancer undergoing definitive breast surgery or mastectomy
Excludes patients with inflammatory breast cancer or extensive nodal disease.
Melanoma:
Primary cutaneous melanoma with a Breslow thickness >1.0 mm, or those with features concerning for nodal metastasis (e.g., ulceration, high mitotic rate) and clinically negative nodes (cN0).
Other Cancers:
Vulvar cancer, penile cancer, and selected cases of gastric, lung, and head and neck cancers with limited nodal involvement potential.
Contraindications:
Previous ipsilateral axillary or inguinal surgery/radiation, known distant metastases, inability to tolerate surgery, or multifocal/extensive primary tumors with high likelihood of nodal involvement.
Preoperative Preparation
Patient Counseling:
Informed consent detailing the procedure, risks, benefits, potential for false negatives/positives, and alternatives
Discussion of potential complications like infection, bleeding, nerve injury, and lymphedema.
Radiotracer Administration:
Injection of the radiotracer (e.g., 99mTc-sulfur colloid) intradermally or subcutaneously around the primary tumor site, typically 2-4 hours prior to surgery
May involve blue dye injection simultaneously or shortly before surgery to aid visualization.
Imaging:
Preoperative lymphoscintigraphy may be performed to map lymphatic drainage patterns and identify sentinel node location
This aids the surgeon in planning the approach.
Imaging Guidelines:
Injection technique should ensure tracer uptake by lymphatic channels
Multiple injection sites may be used for larger tumors or those with complex lymphatic drainage
Avoidance of intravenous or intratumoral injection.
Procedure Steps
Localization:
During surgery, the surgeon uses a handheld gamma probe to detect radioactivity from the radiotracer in the sentinel lymph nodes
The loudest signal indicates the location of the sentinel node(s).
Identification:
Incision is made over the area of highest radioactivity detected by the gamma probe
If blue dye was used, the blue-stained node(s) are also identified.
Excision:
The identified sentinel node(s) are carefully dissected and removed
It is crucial to excise all radioactive and/or blue-stained nodes
Multiple sentinel nodes may be present.
Confirmation And Analysis:
The removed sentinel nodes are sent for histopathological examination, including frozen section analysis if available and clinically indicated
If frozen section is positive, completion lymphadenectomy may be considered, though current trends favor observation or selective dissection based on tumor type and patient factors.
Postoperative Care
Wound Care:
Standard surgical wound care, including dressing changes and monitoring for signs of infection
Patients are encouraged to move the affected limb to prevent stiffness.
Pain Management:
Analgesics as needed for incisional pain
Monitoring For Complications:
Close observation for signs of infection, seroma formation, hematoma, or compromised wound healing
Lymphedema monitoring in the long term.
Follow Up:
Follow-up appointments are scheduled to assess wound healing, monitor for complications, and review histopathology results
Subsequent management (adjuvant therapy, further surgery) is determined based on the sentinel node status and other prognostic factors.
Complications
Early Complications:
Seroma formation, hematoma, wound infection, temporary nerve paresthesia, bleeding
Rare complications include lymphatic leak or significant allergic reaction to the tracer.
Late Complications:
Lymphedema of the ipsilateral limb is the most significant late complication, though its incidence is lower with SLNB compared to ALND
Chronic pain or altered sensation in the area of dissection.
Prevention Strategies:
Meticulous surgical technique to minimize tissue trauma, appropriate wound closure, judicious use of drains if necessary, and patient education on limb care and early recognition of lymphedema symptoms
Careful identification of all sentinel nodes to avoid leaving behind metastatic nodes.
Prognosis
Factors Affecting Prognosis:
The most critical prognostic factor is the status of the sentinel lymph node(s)
Positive sentinel nodes indicate the presence of metastasis and generally confer a poorer prognosis
Factors like tumor size, grade, lymphovascular invasion, and hormone receptor status also play a significant role.
Outcomes:
For node-negative patients identified by SLNB, prognosis is generally excellent, and they can avoid the morbidity of ALND
For node-positive patients, SLNB guides further management, which may include adjuvant chemotherapy, radiation therapy, or hormone therapy, significantly impacting long-term outcomes.
Follow Up:
Long-term follow-up is essential to monitor for local recurrence, distant metastasis, and the development or progression of lymphedema
Regular physical examinations and imaging as indicated by clinical guidelines are crucial.
Key Points
Exam Focus:
Understanding the indications for SLNB, the role of radiotracer and blue dye, the technique of localization with a gamma probe, and the interpretation of sentinel node status for staging and treatment planning
Differentiate between SLNB and ALND in terms of indications and morbidity.
Clinical Pearls:
Ensure adequate time for tracer uptake before surgery
Perform lymphoscintigraphy if lymphatic drainage is unclear
Use a combination of radiotracer and blue dye for maximum sensitivity
Carefully document the number and location of sentinel nodes removed
Always confirm radioactivity in removed nodes with the gamma probe.
Common Mistakes:
Failure to inject tracer correctly, inadequate waiting time for uptake, misinterpretation of gamma probe signals, incomplete removal of all radioactive nodes, and performing SLNB in patients with absolute contraindications
Over-reliance on frozen section without considering permanent pathology for definitive management decisions.