Facilitating the Search for the Sentinel Node

The discovery by Morton and co-workers caused others to search for more rapid and less technically demanding methods of locating sentinel lymph nodes. Alex and Krag [37] described the use of a labeled colloid in combination with a gamma-detecting probe to locate the sentinel node in patients with melanoma. This technique was much simpler than the original method described by Morton and colleagues. Uren and colleagues showed that the standard lymphoscintigra-phy technique, which had been in routine use to determine which node fields drained melanoma primary sites, could be modified to allow the exact location of the sentinel nodes to be marked on the skin. This information could then be used to aid in rapid surgical location of sentinel nodes [24,25]. Digital gamma cameras were found to be important in this process as they allowed dynamic studies to be performed, with lymph channels followed until they were seen entering the sentinel nodes. Because some tracer may pass onward quite rapidly to second-tier nodes, not all radioactive nodes are sentinel nodes and only the dynamic phase of the study allows the true sentinel nodes to be identified. A second advantage of the dynamic acquisition is that an estimate of the speed of lymph flow can be obtained [26,27], which helps the surgeon time the injection of blue dye prior to surgery, as well as allowing the surface location of all sentinel nodes to be marked on the skin. It is very important that this marking procedure occur with the patient lying in the same position that they will be in at the time of surgery, otherwise the mark will not overlie the node. The depth of the node from the skin surface can also be measured, which is a further aid to its surgical identification. Unusual drainage pathways are defined and any interval nodes between the primary melanoma site and the draining node field can be marked. When the patient presents to the operating theater following lymphoscintigraphy with an ''X'' marking the location of the sentinel node on the skin and a depth measurement, it facilitates the operative procedure and, in most patients, the senti-

Lymph Node Locations Feet
Figure 4 Blue dye injected into interdigital clefts to demonstrate lymphatic channels passing proximally in the foot toward the groin, thus facilitating cannulation for radiological lymphangiography.

nel node is rapidly found at the appropriate depth, staining blue with a blue channel entering one side of the node. Surgeons require a shorter training period to accurately excise the sentinel node using this method.

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