Sentinel Lymph Node Biopsy in Gynaecological Cancer
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Direct answer
Sentinel lymph node biopsy identifies and removes the first lymph node or nodes that drain a tumour, so that nodal status can be assessed without a full lymphadenectomy. It is used in early cervical cancer, selected endometrial cancer and vulval cancer, and it relies on blue dye, radioactive tracer or fluorescence. When the sentinel node is negative and mapping is adequate, the wider pelvic dissection is usually avoided.
What you must remember
- Tracers: Blue dye, technetium-99m radiocolloid and indocyanine green fluorescence, often combined to improve detection.
- Cervical injection: Tracer is injected into the cervix at the 3 and 9 o'clock positions, both superficially and deeply.
- Cervical indication: Early, low-volume disease, classically tumours up to about 2 cm, with protocols varying.
- Endometrial indication: Selected early endometrial cancer, where the sentinel node guides whether lymphadenectomy is needed.
- Side-specific rule: If no sentinel node is seen on one side in high-risk disease, a lymphadenectomy on that side is usually done.
- Ultrastaging: Serial sectioning and immunohistochemistry detect micrometastases and isolated tumour cells.
- Vulval indication: Unilateral tumours up to about 4 cm without clinical nodes are the classic setting for inguinofemoral sentinel biopsy.
A technique in five steps
A 50-year-old with an early endometrial cancer and a low-risk profile is considered for mapping. The steps show how the node is found and assessed.
- Pre-operative injection: Radiotracer is often injected on the day before surgery, while dye is given at the time of the operation.
- Lymphatic mapping: A gamma probe or fluorescence camera localises the hot or fluorescent node, and blue staining helps visually.
- Node removal: The sentinel node is excised first, the basin is checked for other suspicious nodes, and any such nodes are removed too.
- Side-specific decision: If no sentinel node is detected on one side, a side-specific lymphadenectomy is performed for high-risk disease.
- Ultrastaging: The node is serially sectioned and stained, and immunohistochemistry checks for small deposits before the result is reported.
Mapping failure is recorded in the operative note, because it changes the decision on lymphadenectomy. Bilateral mapping is aimed for in cervical cancer, which makes a negative result more reliable.
Where the exam tries to catch you
The exam loves the difference between mapping and lymphadenectomy.
- Trap: Assuming a negative sentinel node means no nodal disease at all Correct: False negatives occur, which is why ultrastaging is done and mapping failure rules are applied.
- Trap: Using sentinel biopsy in a bulky or widely spread cervical tumour Correct: Mapping is reserved for early, low-volume disease, and bulky disease needs fuller nodal assessment by imaging or lymphadenectomy.
- Trap: Ignoring a failed mapping on one side Correct: A side-specific lymphadenectomy is needed on that side in high-risk endometrial cancer rather than assuming the node is negative.
Frequently asked questions
Which tracers are used for sentinel lymph node mapping in cervical cancer?
Blue dye, technetium-99m radiocolloid and indocyanine green are the main tracers for sentinel node mapping in cervical cancer. Dual tracer use improves detection rates. Surgeons choose tracers based on local availability and protocol.
Where is the tracer injected for cervical sentinel node mapping?
The tracer is injected into the cervix at the 3 and 9 o'clock positions, both superficially and deeply. This route drains the cervical lymphatics towards the pelvic sentinel node. Injection technique affects the detection rate.
What is the side-specific rule in endometrial sentinel node biopsy?
The side-specific rule means that if no sentinel node is detected on one side, a lymphadenectomy is performed on that side in selected high-risk endometrial cancer. This avoids missing nodal disease after a failed mapping. Lymphadenectomy is not needed when mapping succeeds on both sides.
What is ultrastaging in sentinel node biopsy?
Ultrastaging is serial sectioning and immunohistochemistry of the sentinel node to detect micrometastases and isolated tumour cells. It finds deposits that routine haematoxylin and eosin sections can miss. Its results can influence adjuvant treatment decisions.
Which gynaecological cancers use sentinel node biopsy?
Sentinel node biopsy is used in early cervical cancer, selected endometrial cancer and early vulval cancer. Its use depends on tumour size, stage and institutional protocol. Vulval mapping is standard for unilateral tumours under about 4 cm without clinical nodes.