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 radi olabeled colloid and facilitate SLN mapping at the time of surgery we exami ned whether residual radioactivity from preoperative lymphoscintigraphy cou ld be used to accurately identify SLNs during surgery 18 to 24 hours later Methods, Forty-six patients with newly diagnosed melanoma underwent injecti on of 0.22-mu m filtered technetium 99m-labeled sulfur colloid followed by lymphoscintigraphy. Patients returned the next day for SLN biopsy with Isos ulfan blue dye and the hand-held gamma-probe to identify SLNs. Thirty of 46 patients underwent repeat imaging before operation. No patient had reinjec tion of radiocolloid. Results. Ninety-five SLNs were identified on initial lymphoscintigraphy, an d repeat imaging on the day of surgery confirmed all SLNs previously identi fied. A total of 122 SLNs (2.65 per patient) were resected from 58 basins. Eighty-four (66%) of 122 SLNs stained blue, and 218 (97%) of 122 SLNs had i n vivo gamma-counts greater than 4 times background. Microscopic metastases were present in 13 (10.7%) of 122 SLNs in 12 (26.1 %) of 46 patients. Ther e have been no recurrences over a mean follow-up time of 320 days. Conclusions. Intraoperative gamma-probe detection combined with blue dye in jection is highly effective in identifying SLNs 18 to 24 hours after inject ion of 0.22-mu m filtered Tc-99m-sulfur colloid. Reinjection of radio collo id is not required. This technique avoids radiopharmaceutical administratio n in the operating room, minimizes radiation exposure, and increases schedu ling flexibility.