Can ultrasound patterns predict invasion of the sentinel node in melanoma patients?

The present article evaluated the specific appearance of cancer-invaded lymph nodes on ultrasound in patients with melanoma undergoing a sentinel node procedure.

The first place melanoma spreads to (metastasizes) is in the nearby lymph nodes. Once a lymph node is invaded, melanoma patients usually have poorer survival rates. To find out whether melanoma cells have spread to the nearby lymph nodes the doctors do a procedure called a sentinel lymph node biopsy. A sentinel node (SN) is the first lymph node melanoma is likely to spread to. During this test, the doctor injects a small amount of radioactive substance and sometimes a blue dye into the area of the melanoma and then checks which lymph node “lights up” or turns blue following lymph drainage from the area. This SN is removed and looked at under a microscope (biopsied). If the SN is not melanoma-invaded, it is unlikely the other nodes are affected. This procedure can spare the patients of complications such as impaired lymph drainage. 

A less invasive approach for finding the SN is ultrasound guided fine needle aspiration cytology (FNAC). This means that the doctor, guided by the ultrasound, inserts a small needle into the suspected SN and takes a sample of the tissue for cell analysis. The SN is then removed only if the FNAC is positive for melanoma cells.

This study included 400 melanoma patients who were scheduled to undergo a SN procedure between July 2001 and December 2007. Identified SN were examined using ultrasound and FNAC was done to check the node for cancer. Ultrasound patterns of examined lymph nodes were carefully evaluated and compared to overall survival. 

The most common lymph node patterns that predicted melanoma spread were peripheral perfusion, or PP (blood flow around the outer borders of the node), a balloon-shaped lymph node and loss of central echoes (no ultrasound signal in the center of the node meaning that a mass has formed). The overall survival calculated based on PP was 81% if this pattern was present and 92% if absent. Based on loss of central echoes the overall survival was 49% compared to 92% when echoes were present. Similarly, the overall survival for the presence and absence of balloon-shaped lymph nodes was 48% and 92%, respectively. 

In summary, US guided FNAC identified up to 65% of all sentinel node metastases. Peripheral perfusion, loss of central echoes and balloon-shaped lymph nodes were the most important patterns suggesting melanoma involvement of the SN. Either one or a combination of these patterns is highly predictive of melanoma involvement. 

It is important to note that ultrasound in an operator-dependent procedure, meaning that doctors may have different opinions regarding the presence or absence of a certain pattern. Special training is also required to effectively assess lymph nodes using ultrasound.