Lymphoscintigraphy, or lymphatic mapping, is a nuclear medicine scan undertaken by Nuclear Medicine specialists 12 to 24 hours before surgery.

A tiny dose of radioactive tracer is injected into the skin around the melanoma which, over a period of 2-3 hours, travels to the lymph nodes or glands. The first lymph node which drains the melanoma is called the sentinel node.  A gamma camera is used to identify the relevant lymph channels and lymph nodes. The skin overlying the sentinel node is marked with a small tattoo dot. An ultrasound examination is often performed at the same time to assess the size and any abnormal characteristics of the lymph nodes.

Lymphoscintigraphy greatly assists surgery by identifying the sentinel lymph nodes prior to surgery. During the operation, a blue dye is then injected around the primary melanoma site. The dye then travels in lymphatic channels and stains the sentinel lymph nodes blue.

It has been found that the combined use of lymphoscintigraphy prior to surgery, blue dye and a small hand-held gamma probe (a mini Geiger counter) provides the greatest accuracy in identifying the sentinel nodes.

A few practical issues for patients

You will find the isotope injection stings, similar to that of local anaesthetic. There may be some residual redness for an hour or two afterwards.

There may be more than one node identified. Please do not try to wash off the skin markings.

There is no risk to you from the radioactive marker as the dose is very small and it looses its radioactivity very quickly.