What is a sentinel lymph node?
The sentinel lymph node is the first lymph node ("lymph gland") to receive lymphatic drainage from a tumor. It stands sentinel over the tumor, so to speak.
What is the lymphatic drainage?
Lymphatic systrem refers to a collection of vessels that, like the system of blood vessels, circulates fluid through the tissues. The lymnphatic drainage refers to the manner in which tissue fluid, or lymph, is draned from the body and returns to a central location - in this case, a lymph gland. The lymph fluid looks milky.
Why do a biopsy of the sentinel node?
Examination of the sentinel node ("gland") is performed to learn whether that node does or does not have tumor cells within it.
How does a tumor spread?
Tumors have only three ways of spreading:
- By local invasion of adjacent tissue;
- Through the blood stream; and
- Through the lymphatic system.
Some tumors spread preferentially by the lymphatic system, meaning that they tend to spread by this method.
How is it determined which is the sentinel node?
Which lymph node is the sentinel node for a given tumor is determined by injecting around the tumor a tracer substance that will travel through the lymphatic system to the first draining (sentinel) node and identify it. The tracer substance may be blue dye that can be visually tracked or a radioactive substance or colloid that can be detected as with a Geiger counter.
What does the sentinel-lymph-node biopsy show?
Biopsy of the sentinel lymph node reveals whether there are or are not lymphatic metastases, which are tumor cells that have journeyed from the original primary tumor into the lymphatic drainage system.
If the sentinel node contains tumor cells, removal of more nodes in the area may be warranted. If the sentinel node is normal, it is unnecessary to perform an extensive dissection of the regional lymph-node basin.
Is the use of the sentinel-lymph-node biopsy common?
Yes. Sentinel-lymph-node biopsy has, for example, become a standard technique for determining the nodal stage of the disease in some patients with malignant melanoma and with breast cancer.