Overview
Definition:
Sentinel lymph node biopsy (SLNB) is a surgical procedure to identify and remove the first lymph node(s) that a tumor drains into (the sentinel nodes)
This allows for precise staging of nodal metastasis without the need for more extensive lymphadenectomy, thereby reducing morbidity.
Epidemiology:
SLNB is primarily used in early-stage breast cancer and melanoma
In breast cancer, it is indicated for clinically node-negative patients
For melanoma, it is used for primary tumors >1 mm in depth or with high-risk features
Incidence varies based on cancer type and stage, with millions of procedures performed globally annually.
Clinical Significance:
Accurate nodal staging is critical for treatment planning, prognosis, and preventing over-treatment
SLNB minimizes the complications associated with axillary lymph node dissection (ALND), such as lymphedema, seroma, and nerve injury, while providing essential prognostic information.
Indications And Contraindications
Indications:
Early-stage breast cancer (clinically node-negative axilla)
Melanoma with primary tumor >1 mm Breslow depth, ulceration, or high mitotic rate
Vulvar cancer
Penile cancer
Gastric cancer (in select cases).
Contraindications:
Clinically palpable lymphadenopathy (suggests widespread disease)
Previous extensive lymph node dissection in the region
Prior radiation therapy to the nodal basin
Pregnancy (relative contraindication for radioactive tracers)
Known distant metastasis.
Preoperative Preparation
Patient Evaluation:
Thorough clinical assessment to rule out palpable lymphadenopathy
Review of imaging (mammography, ultrasound, CT, MRI) for nodal involvement
Assessment of comorbidities.
Procedure Planning:
Choice of tracer: Blue dye alone, radioactive tracer (e.g., Technetium-99m sulfur colloid) and blue dye, or near-infrared fluorescent dye (e.g., Indocyanine green)
Coordination with nuclear medicine for radioactive tracer injection
Patient counseling regarding procedure, risks, and benefits.
Informed Consent:
Detailed explanation of the procedure, potential complications (e.g., allergic reaction to dye, failure to identify sentinel node, false negative/positive results), and alternative management options.
Procedure Steps Blue Dye Technique
Dye Injection:
Typically injected intradermally or subcutaneously around the tumor or areola (for breast cancer) or at multiple points around the primary melanoma excision site, 5-10 minutes before incision
The dye extravasates into the lymphatic channels and migrates to the sentinel nodes.
Lymphatic Identification:
The surgeon identifies blue-stained lymphatic channels leading to a blue-colored lymph node
Dissection is performed carefully along these channels to isolate the sentinel node(s).
Node Excision:
The blue-colored sentinel node(s) are excised
Multiple nodes may be blue
Multiple sentinel nodes should be identified and removed if possible.
Confirmation And Closure:
The specimen is sent for pathological examination
Hemostasis is achieved
Incision is closed in layers
A drain may be placed if extensive dissection is performed.
Pathological Examination
Intraoperative Analysis:
Frozen section analysis of sentinel nodes can be performed to guide immediate management (e.g., proceed to ALND if positive)
However, permanent histology is definitive.
Permanent Histology:
Detailed examination of excised sentinel nodes for micrometastases and macrometastases
Serial sectioning and special stains (e.g., immunohistochemistry for cytokeratins) improve detection of occult metastases.
Reporting Criteria:
Pathology reports should clearly state the number of sentinel nodes examined, the number positive, and the size of the largest metastasis (macrometastasis vs
micrometastasis)
This guides further treatment decisions.
Complications
Early Complications:
Allergic reaction to the blue dye (rare, can range from mild skin rash to anaphylaxis)
Localized skin discoloration at the injection site (transient)
Seroma or hematoma
Infection at the incision site.
Late Complications:
Persistent blue staining of the skin
Lymphedema (significantly less common than with full ALND)
Nerve injury (rare)
Chronic pain or discomfort.
Prevention Strategies:
Careful injection technique
Careful surgical dissection to avoid damage to surrounding structures
Prompt identification and management of any signs of infection
Patient education on wound care and monitoring for lymphedema.
Prognosis And Follow Up
Prognostic Factors:
The presence and size of metastasis in the sentinel lymph node are the most significant prognostic factors
Other factors include primary tumor characteristics (stage, grade, margins) and patient factors.
Outcomes With Slnb:
For node-negative patients, SLNB has excellent accuracy and low morbidity
For node-positive patients, the prognosis depends on the extent of nodal involvement and whether further treatment is undertaken.
Follow Up:
Regular clinical examination and follow-up imaging as per cancer-specific guidelines to monitor for recurrence
Patient education on self-monitoring for signs of lymphedema or recurrence.
Key Points
Exam Focus:
Indications for SLNB in common cancers (breast, melanoma)
Role of blue dye as a tracer
Identification of sentinel node
Complications specific to blue dye
Pathological assessment of sentinel nodes.
Clinical Pearls:
Inject the dye slowly and allow adequate time for migration
Use a gamma probe if radioactive tracer is used concurrently
If multiple blue nodes are found, all should be excised
Consider a multidisciplinary team approach for complex cases.
Common Mistakes:
Inadequate injection volume or technique
Insufficient time for dye migration
Incomplete retrieval of all identified blue nodes
Over-reliance on intraoperative frozen section without permanent histology confirmation
Failure to consider alternative nodal basins in recurrent disease.