Background: The value of targeted high-resolution ultrasound (US) examination in detecting sentinel lymph node metastases in patients with newly diagnosed primary cutaneous melanomas has not yet been fully evaluated. The aim of this study was to determine the threshold size of metastatic melanoma deposits in SLNs able to be detected by targeted US examination before initial melanoma surgery.
Methods: A total of 304 patients presenting with primary cutaneous melanomas had SLNs identified by lymphoscintigraphy and then examined in situ by the same physician with high-resolution US. Within 24 hours, the SLNs were removed for histopathologic assessment of sections stained conventionally and with immunohistochemical markers for S100 protein and HMB45 antigen.
Results: Metastatic disease was present in SLNs from 33 node fields in 31 patients. The US results in seven of these cases were suggestive of metastatic disease. Twenty-six node fields contained positive nodes not detected by US. Undetected deposits had diameters <4.5 mm.
Conclusions: These results suggest that a targeted US examination of SLNs can detect metastatic melanoma deposits down to approximately 4.5 mm in diameter. However, most metastatic melanoma deposits in SLNs are considerably smaller than this at the time of initial staging, and US therefore cannot be considered cost-effective in this setting.