sentinel lymph node
Meaning of sentinel lymph node: The node a surgeon samples instead of clearing a whole basin, chosen not for being nearest but for being first in line.
Definition of sentinel lymph node
A sentinel lymph node is the first node that lymph fluid reaches when it drains away from a tumor, and therefore the first place cancer cells traveling by that route would arrive. There can be more than one. Because drainage follows fixed paths, the sentinel node can be located and examined as a stand-in for the whole group behind it.
How is it found?
A tracer is injected into the tissue around the tumor and allowed to travel the same route the lymph takes. Two tracers are common: a blue dye that stains the node visibly, and a weakly radioactive substance that a handheld probe detects through the skin. Using both together finds more nodes than either alone. The surgeon follows the signal and removes the node or the few nodes that light up, a procedure called sentinel lymph node biopsy. Whatever the tracer reaches first counts, even when a closer lymph node is left in place.
Why sample one node instead of many?
Removing an entire group of nodes was the older approach, and it carries a lasting cost. Cutting the drainage channels leaves fluid with nowhere to go, and the arm or leg swells, sometimes permanently. Nerve injury, stiffness and wound problems are more common as well. If the first node in the path is clear, the ones beyond it are usually clear too, so a full lymph node dissection can be avoided in most people. The trade is a small chance of missing disease against a large reduction in lasting harm.
Where is the idea used?
| Cancer | Node group usually mapped |
|---|---|
| Breast | Armpit on the same side |
| Melanoma | Depends on the site; drainage can cross the midline |
| Vulva and penis | Groin |
| Head and neck | Neck levels on the same side |
Melanoma of the trunk shows why mapping is needed rather than assumption. The same patch of skin can drain to the armpit, to the groin or up into the neck, and the pattern differs between people, so the node that matters cannot be predicted from the position of the tumor alone.
Also known as
Used in a sentence
The sentinel lymph node was identified with dye and isotope and sent for examination.
Good to know
The sentinel node is defined by drainage rather than distance, so it is not always the node closest to the tumor, and lymph channels blocked by disease can divert flow and produce a falsely clear result.
Word origin
Where “sentinel lymph node” comes from
Sentinel comes through Italian from sentinella, a watchman; lymph from the Latin lympha, meaning clear water; node from nodus, a knot.