Monday, January 30, 2012
LYMPHOSCINTIGRAPHY AND SENTINEL LYMPH NODE EVALUATION
For certain types of cancers (Melanoma, Merkel Cell Carcinoma, and other Cancers showing aggressive characteristics), it is sometimes helpful to perform lymphoscintigraphy and sentinel lymph node excision.
The lymphatic system is composed of channels running throughout the body that pick up lymphatic fluid and cells (fluid and cells within the tissues), filter this fluid through lymph nodes, and eventually return the fluid and cells to the heart and back into the blood stream.
Some cancers with more aggressive characteristics have the potential for spreading to lymph nodes. Lymph nodes act as a filter and trapping mechanism to capture cells that may be harmful to the body (cancer cells and infection). It is helpful in terms of treatment, predicting prognosis, and improving the cure rate and survival if we can determine if these cancers have spread to regional lymph nodes.
The Sentinel Lymph Node is the first lymph node that will accept drainage from a particular region of the body. For example, if we have a more aggressive cancer on the face, there is a chance that the cancer could spread to a lymph node or nodes in the neck. There are multiple lymph nodes in the neck, so the trick is to determine to which lymph node or nodes this cancer would spread if it decided to get into the lymphatic system and spread. To determine the first node or nodes that may accept drainage, the patient is evaluated in the Nuclear Medicine Department of Radiology the morning of surgery or the day before. A radioactive tracer is injected near the cancer, and this tracer is picked up by the lymphatic system and migrates within the lymphatic vessels until it reaches the sentinel lymph node. By taking X-rays during this process, the radiologist is able to determine where this sentinel lymph node is located. A mark is usually made over the lymph node to identify it. Sometimes, there is more than one lymph node identified, and sometimes the lymphatic system does not pick up the tracer and no sentinel lymph node can be detected. This pre-operative study is called Lymphoscintigraphy. The patient then presents to the surgical suite, and the primary cancer is removed and the defect reconstructed. The sentinel lymph node is then addressed. An incision is made over the marking, and using a sterile Nuclear Detection Probe, the dissection into the lymph node basin is performed until a "radioactively hot" node(s) is identified. The lymph node(s)is removed and sent for permanent pathology. For most cases, it takes about a week to get the results. Keep in mind, just because we have identified and removed a sentinel lymph node, this does not necessarily mean that the lymph node is involved with cancer. It just means that if the cancer is going to spread into the lymphatic system, this will be the first lymph node that it goes to.
If no cancer is identified in the lymph node, that is a good sign which tells us at the current time, the cancer has not spread into the lymphatic system. If we identify cancer in the sentinel lymph node, additional surgery is usually necessary (complete lymph node dissection of the all lymph nodes in that particular regional basin).