Basic Science
The Lymphatic System
A Lymph Node
A simple understanding of the lymphatic system is key to understanding the course of spread of malignant melanoma since this is its primary channel to spread around the body; or in medical terms metastasise.
Lymphatic capillaries are an extensive network of channels in the skin and other organs whose normal function is to return tissue fluid (Lymph) to the venous blood system but via regional lymph node groups.
Regional Lymph nodes
Thoracic Duct (click for large)
These are staging posts along the lymphatic network which in health have a protective immunological role.
Lymph then moves centrally along larger lymphatic vessels and via other lymph node groupings eventually to reach the thoracic duct in the left neck where lymph returns to the venous blood.
Where are the Regional Lymph Nodes?
It is essential to know where the regional nodes for each part of the body are to effectively clinically monitor the spread of melanoma. Although doctor’s learn these facts in anatomy classes, we think it is most useful for patients to know which nodes are most likely to be affected.
With a little bit of knowledge you can add examination of lymph nodes to your disease surveillance regime and alert the doctor if you think you notice a change in the size of the nodes. Remember, many other illnesses (not all cancer) can affect the size of the nodes but as a rule of thumb, if you have melanoma and notice a change in the nodes it is significant.
General rules of lymphatic drainage
Leg - groin nodes
Arm - nodes in the axilla (arm pit)
Trunk - axilla or the groin or to both. They do not usually cross the midline. However a melanoma arising in the midline of the trunk (front or back) can disseminate malignant cells to lymphatic capillaries that drain to lymph nodes in either axilla or in either groin.
Head & Neck - to a rich network of lymphatic vessels that can drain to multiple lymph node groups in the neck and can cross the midline.