Preoperative Sentinel Lymph Node Non-visualisation in Head and Neck Melanoma: A 17-Year Retrospective Cohort Study

Skin cancer is a growing concern worldwide, but not all skin cancers behave the same way. Among them, melanoma is the most dangerous form, capable of spreading from the skin to other parts of the body. When a doctor finds a melanoma, one of the most critical questions is whether the cancer has begun to travel through the body's drainage system. The body uses a network of tiny vessels called lymphatics to carry fluid away from tissues, much like a city's storm drains carry rainwater away from streets. Along these paths are small filters called lymph nodes that trap germs and, unfortunately, cancer cells. To check if melanoma has started to spread, surgeons often look for the very first node that drains fluid from the tumor site, known as the sentinel node. If this first node is clear, the cancer is likely contained; if it contains cancer cells, the disease has begun to spread, changing the treatment plan entirely.

This process works well for melanomas on the arms or legs, where the drainage paths are usually straightforward. However, the head and neck region is a complex landscape of muscles, nerves, and blood vessels, creating a tangled web of drainage routes that can be unpredictable. Sometimes, the fluid from a tumor on the face or scalp does not flow to a single, clear destination. In some cases, the fluid seems to vanish or scatter in directions that standard imaging cannot catch. This phenomenon, where doctors cannot see the first draining node on preoperative scans, has been a source of uncertainty. It raises a difficult question for patients and surgeons: if the map is blank, does that mean the cancer is hiding, or is it simply a matter of anatomical variation?

A team of researchers at The Christie NHS Foundation Trust in Manchester, United Kingdom, set out to answer this question by looking back at nearly two decades of patient records. They examined 400 adults who had undergone surgery to remove melanomas from the head and neck between 2007 and 2024. Before the surgery, every patient received a special scan called lymphoscintigraphy, where a tiny amount of radioactive tracer is injected into the skin near the tumor. This tracer travels through the lymphatic system, lighting up the path on a camera so surgeons can see exactly where the fluid is going. The researchers focused specifically on the 35 patients, representing 8.8 percent of the group, whose scans failed to show a clear path to a sentinel node.

The study revealed that this inability to see the drainage was not random. It happened significantly more often in older patients, with a median age of 76 for those with invisible drainage compared to 65 for those with visible drainage. The location of the tumor also mattered greatly. Melanomas on the scalp or the cheek were much more likely to result in invisible drainage, while tumors near the ear almost never caused this issue. Interestingly, the researchers found that the size of the tumor or whether the skin was broken and ulcerated did not seem to determine if the drainage would be visible. This suggests that the failure to see the node is less about how aggressive the cancer is and more about the patient's age and the specific geography of the head and neck where the tumor sits.

Perhaps the most reassuring finding for patients was that not being able to see the drainage on a scan did not mean the cancer was more dangerous. The researchers tracked the patients for an average of three years and eight months. They found that the rate of cancer returning was nearly identical for both groups: about 31 percent of those with invisible drainage saw a recurrence, compared to 28 percent of those with visible drainage. Similarly, the overall survival rates were not significantly different between the two groups. This indicates that a blank scan is not a sign of a hidden, aggressive disease, but rather a technical limitation caused by the complex anatomy of the face and scalp or the natural changes in the lymphatic system that come with aging.

The study also looked at why this might happen. In the head and neck, the first draining node can sometimes sit so close to the injection site that the bright signal from the injection hides the node itself. Previous surgeries or scarring in the area can also block or reroute the flow. The researchers noted that as people age, their lymphatic system can become less efficient at moving fluid, which might explain why older patients were more likely to have invisible nodes. While the study was limited by its retrospective nature and the relatively small number of patients with invisible drainage, the data provides a clear picture. It suggests that when a scan fails to show a node in an older patient with a head or neck melanoma, it is likely a reflection of the patient's anatomy and age rather than a sign that the cancer has already spread in a way that cannot be detected.

Ultimately, this research helps to calm the anxiety that often accompanies a missing scan result. For surgeons and patients alike, the inability to visualize the sentinel node in the head and neck region appears to be a common occurrence tied to specific physical factors, not a harbinger of poor outcomes. The findings suggest that the standard approach of careful monitoring remains appropriate, even when the map is blank. While larger studies are needed to confirm these results across different hospitals and populations, this work offers a significant step toward understanding the unique challenges of treating melanoma in the complex terrain of the human head and neck.