From the Guidelines
Sentinel nodes are typically located in the regional lymph node basins closest to the primary tumor, such as the axilla, internal mammary chain, or supraclavicular region in breast cancer, and can be identified using lymphoscintigraphic imaging or intraoperative gamma probe detection 1. The location of sentinel nodes can vary depending on the type of cancer and the area of the body affected.
- In breast cancer, sentinel nodes are commonly found in the axilla, but can also be in the internal mammary chain or supraclavicular region 1.
- In other types of cancer, such as melanoma, sentinel nodes can be located in the lymphatic basin that drains the area where the tumor is located, such as the neck, axilla, or groin.
- The use of lymphoscintigraphic imaging can help identify the location of sentinel nodes, with a frequency of visualization of axillary sentinel nodes typically in the 60% to 90% range 1.
- The location of sentinel nodes can also be identified using intraoperative gamma probe detection, which is more sensitive than lymphoscintigraphic imaging in detecting axillary sentinel nodes 1. The most recent study on sentinel lymph node biopsy in endometrial cancer found that sentinel lymph nodes were most commonly located in the external iliac region, followed by the obturator and internal iliac regions 1. Key factors that can affect the identification of sentinel nodes include the type of radiocolloid used, the route of injection, and the time from injection to imaging 1.
- The use of very small particles may result in a higher frequency of visualization of nodes, but this is somewhat controversial, as some studies have suggested larger colloids are preferable 1.
- Injections in the subdermal skin overlying the tumor, or in the periareolar area, may be more effective than perilesional injections only in visualizing sentinel nodes 1.
From the Research
Location of Sentinel Nodes
The location of sentinel nodes in breast cancer patients has been studied extensively. According to 2, sentinel lymph nodes (SLNs) are typically found in the axilla, with 97.8% of patients having at least one SLN in this region. The study also found that approximately 50% of SLNs were located in the mid or posterior group of Level I axillary nodes, rather than the anterior group.
Axillary Lymph Node Location
The location of axillary lymph nodes can vary, with some studies suggesting that they can be found in the anterior, mid, or posterior groups of Level I axillary nodes. As noted in 2, the use of SPECT/CT lymphoscintigraphy can help to precisely locate the SLN in the axilla.
Factors Influencing Sentinel Node Location
Several factors can influence the location of sentinel nodes, including the location of the primary tumor in the breast. However, as stated in 2, axillary lymphatic drainage from the breast is not exclusively to the anterior group of Level I nodes, and may drain to the mid axilla and/or posterior group in about 50% of patients with breast cancer.
Identification of Sentinel Nodes
Sentinel nodes can be identified using various techniques, including lymphoscintigraphy and radioguided biopsy. As described in 3, lymphoscintigraphy associated with radioguided biopsy of the sentinel node is a useful method for localizing the axillary SLN in breast cancer patients. The study found that lymphoscintigraphy successfully revealed lymphatic drainage in 98% of patients, and the axillary SLN was identified in 96% of patients.
Size of Sentinel Node Tumor Deposits
The size of tumor deposits in the sentinel node can also be an important factor in determining the extent of axillary lymph node involvement. According to 4, patients with sentinel node tumor deposits ≤5 mm had three or fewer positive nodes, and 95% were sentinel node-positive only. This suggests that patients with small tumor deposits in the sentinel node may benefit from less aggressive axillary dissections.
- Key points about sentinel node location:
- Typically found in the axilla
- Can be located in the anterior, mid, or posterior groups of Level I axillary nodes
- Location can vary depending on the location of the primary tumor in the breast
- Axillary lymphatic drainage from the breast is not exclusively to the anterior group of Level I nodes
- Techniques for identifying sentinel nodes:
- Lymphoscintigraphy
- Radioguided biopsy
- SPECT/CT lymphoscintigraphy
- Factors influencing sentinel node location:
- Location of the primary tumor in the breast
- Size of tumor deposits in the sentinel node
- Lymphatic drainage patterns from the breast to the axilla