Timing of sentinel lymph node mapping after lymphoscintigraphy

Background. Sentinel lymph node (SLN) mapping is an effective technique for staging patients with melanoma. In an attempt to avoid reinjection of radiolabeled colloid and facilitate SLN mapping at the time of surgery, we examined whether residual radioactivity from preoperative lymphoscintigraphy could be used to accurately identify SLNs during surgery 18 to 24 hours later. Methods. Forty-six patients with newly diagnosed melanoma underwent injection of 0.22-μm filtered technetium 99m-labeled sulfur colloid followed by lymphoscintigraphy. Patients returned the next day for SLN biopsy with Isosulfan blue dye and the hand-held γ-probe to identify SLNs. Thirty of 46 patients underwent repeat imaging before operation. No patient had reinjection of radiocolloid. Results. Ninety-five SLNs were identified on initial lymphoscintigraphy, and repeat imaging on the day of surgery confirmed all SLNs previously identified. A total of 122 SLNs (2.65 per patient) were resected from 58 basins. Eighty-four (69%) of 122 SLNs stained blue, and 118 (97%) of 122 SLNs had in vivo γ-counts greater than 4 times background. Microscopic metastases were present in 13 (10.7%) of 122 SLNs in 12 (26.1%) of 46 patients. There have been no recurrences over a mean follow- up time of 320 days. Conclusions. Intraoperative γ-probe detection combined with blue dye injection is highly effective in identifying SLNs 18 to 24 hours after injection of 0.22-μm filtered (99m)Tc-sulfur colloid. Reinjection of radiocolloid is not required. This technique avoids radiopharmaceutical administration in the operating room, minimizes radiation exposure, and increases scheduling flexibility.