Validation of delayed sentinel lymph node mapping for melanoma

Sentinel lymph node mapping using radiolabeled tracer and blue dye is widely accepted and applied for staging melanoma. Common practice involves injection of radiolabeled tracer on the morning of surgery. However, optimal timing of radiolabeled colloid injection with respect to surgery remains debated. Injection on the day before surgery would offer the advantages of increased scheduling flexibility and decreased radiation exposure to the patient and operating room staff. We hypothesized that a single injection of radiolabeled colloid given 24 hours before surgery would be sufficient and would possibly improve intraoperative sentinel lymph node identification.

Ninety-five patients with newly diagnosed cutaneous melanoma underwent injection of radiolabeled colloid and lymphoscintigraphy 18 to 24 hours before surgery for sentinel lymph node mapping and biopsy. Sixty-three patients underwent repeat imaging immediately before surgery, and the images were compared with those obtained the previous day. Intraoperative mapping utilized a hand-held gamma probe and injection of blue dye to identify sentinel lymph nodes.

Two hundred fifty-one sentinel lymph nodes were identified by initial lymphoscintigraphy in 95 patients. Delayed imagingwithout reinjection of radiolabeled tracer compared with the initial lymphoscintigraphy demonstrated no change (71%), clarification of initial ambiguous patterns (10%), or newly identified nodes (19%). Two hundred sixty-one sentinel lymph nodes were resected, of which 79% stained blue. Microscopic metastases were present in 20 sentinel lymph nodes (8%) in 19 patients (20%). All positive nodes contained radioactivity and blue dye.

A single injection of radiocolloid 24 hours before surgery combined with intraoperative blue dye injection identified all sentinel lymph nodes and did not miss any metastatic disease. In addition, delayed imaging may clarify initial ambiguous findings and identify additional nodes at risk for metastasis. This technique produces sentinel lymph node identification rates, harvest rates, and rates of positivity comparable to those reported with the use of injection of radiolabeled tracer on the day of surgery and greatly facilitates the technical and administrative aspects of sentinel lymph node mapping.