Overview

Sentinel node studies are relatively new to Nuclear Medicine. The procedure provides a "road map" showing the direction of lymphatic drainage from around the site of a cancer. Before this procedure was available, the surgeon would make the best guess about the direction of lymph drainage from a tumor to the lymph nodes. The surgeon would then take out many lymph nodes in the area estimated to be the drainage pathway. Those lymph nodes would then be examined microscopically for signs of spread of the tumor.

The Sentinel Node study, however, demonstrates more clearly and precisely the path of lymphatic drainage. This allows the surgeon to take out the specific node (or nodes) that are the first to receive lymphatic drainage from the area around the tumor. If these "sentinel" node(s) do not show any microscopic evidence of tumor, it is very unlikely that any other nodes would contain any tumor cells. Since fewer nodes are removed, the surgery is less extensive and recovery is faster.

The procedure involves no preparation on the part of the patient, other than the usual pre-operative instructions provided by the surgeon.

During The Exam

In Nuclear Medicine, the physician will inject a small amount of radioisotope in the region of the tumor. There are usually 4 to 8 injections, depending on the type of tumor. The injections can feel like bee stings, but the pain usually subsides after a few seconds.

The rest of the exam consists of taking pictures. The technologist and the doctor will work together to look for lymph nodes draining the region around the tumor. If lymph nodes are seen, the doctor will probably use a pen to put a mark on the skin overlying the lymph node to help the surgeon find the nodes.

In the operating room, the surgeon has a probe that detects the radioactivity in the lymph nodes. The probe is used in conjunction with the pictures and skin marks from Nuclear Medicine to identify the sentinel node(s). Once the nodes are removed, they are sent to pathology for microscopic examination for evidence of spread of the tumor.

Safety Issues

As with most Nuclear Medicine studies, the radiation dose from this test is very small. In addition, the surgeon will likely remove much of the skin and the lymph nodes that contain the greatest amount of the injected radioactivity. The rest of the radioactivity will decay quickly. Following surgery, no special precautions are necessary.