Predictive role of imaging in sentinel lymph node dissection for melanoma

A retrospective study of 67 patients with metastatic melanoma was performed to evaluate if imaging from lymphoscintigraphy could predict a higher miss rate if only the most radioactive node were removed. Following protocol for sentinel node biopsy, the surgeon resected all lymph nodes containing radioactivity > 10% of the most radioactive node. A correlation was performed between the radioactive counts of the lymph nodes and the presence of metastases. The percentage of cases in which the most radioactive node was negative for metastasis on pathology was calculated. Two nuclear medicine physicians read the images from lymphoscintigraphy specifically to determine if the first lymph node visualized became less intense than other nodes on later images. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. In 13 of 67 (19%) patients, the most radioactive lymph node was negative for metastasis while a less radioactive node contained metastatic disease. Consensus reading by the nuclear medicine physicians determined that in 9 cases, the first lymph node visualized became less intense than another lymph node on later images. Of the 9 cases, 4 were true positive and 5 were false positive when correlated with intraoperative count rate and pathology. Of the cases where the most radioactive node was not positive on histopathology (n = 13), the consensus reading by the nuclear medicine physicians reported 4 of them (31%). Imaging by lymphoscintigram had a sensitivity 31%, specificity 91%, positive predictive value 44%, and negative predictive value 85% for predicting whether the most radioactive lymph node at surgery would be negative for metastasis at pathology. We conclude that in patients with melanoma, lymphoscintigraphy has high specificity and negative predictive value but modest sensitivity and positive predictive value for detecting when the sentinel node will not be the most radioactive lymph node during sentinel lymph node dissection. These findings support that dynamic imaging by lymphoscintigraphy has a role in surgical planning but that the imaging protocol could benefit from further optimization.