Ultrasound of the sentinel node in melanoma patients: Echo-free island is a discriminatory morphologic feature for node positivity

Unlike breast and thyroid cancer, the use of ultrasound (US)-guided fine needle aspiration cytology (FNAC) for preoperative staging is limited in melanoma. New US morphology criteria have shown that US-FNAC can correctly identify 50% of all involved sentinel nodes (SN) in melanoma patients before surgical excision. The aim of this study was to examine a new criterion: the echo-free island (EFI). A total of 1000 consecutively staged melanoma patients (Breslow thickness>1 or<1 mm, but ulcerated, Clark IV/V or regressed) scheduled for SN staging underwent preoperative US. US morphology items were assessed: peripheral perfusion, loss of central echoes, balloon shape, and EFI. FNAC was performed in case of suspicious and malignant US patterns. All patients proceeded to undergo an SN biopsy or direct completion lymph node dissection (CLND) (in the case of positive FNAC). In all, 57% of the patients were men. The mean/median Breslow thickness was 2.58/1.57 mm. The mean/median follow-up was 56/53 months. SN was positive in 21%. EFI information was available in 95.3%. EFI was seen in 40 patients (4%). EFI sensitivity was 10.8%, specificity was 97.6%, positive predictive value was 50%, and negative predictive value was 80.2%. EFI was significantly correlated to peripheral perfusion (67.5%). There was no correlation to balloon shape or loss of central echoes. Five-year melanoma-specific survival of patients with EFI was significantly worse: 80% versus 92% when absent. The EFI can be useful in the early detection of SN melanoma metastasis. It is an early sign of involvement and thus associated with a decreased survival.