A sentinel lymph node is a node that drains a particular site. In theory a tumor or other lesion that drains to a lymph node will deposit at the sentinel node.
(1) A marker is injected in and around the lesion in question.
(2) The marker may be a dye with an intense color or a radioactive marker.
(3) The lymph nodes draining the site are then examined for tell-tale signs of drainage to one or more lymph nodes.
gamma probe counts > 10 times background count
colored node or colored lymphatics leading to the node
Often both modalities are used since this increases the sensitivity of the method.
Once a sentinel node is identified then it is biopsied and examined microscopically for signs of the parent lesion.
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Specialty: Hematology Oncology, Clinical Laboratory