Sonographic evaluation of clinically occult in-transit and satellite metastases from cutaneous malignant melanoma.

PURPOSE: Our purpose was to assess the potential of ultrasonography (US) in the detection of in-transit or satellite metastases.
MATERIALS AND METHODS: Following a review of the relevant literature, we present the results of a retrospective study based on 2,000 malignant melanoma patients with complete case records. Of these, we selected 600 patients who had a thick melanoma (>1 mm) at presentation but were clinically free of in-transit or satellite melanoma metastases during follow-up. All patients underwent periodic clinical and imaging investigations, as well as US examination of the site of the surgical wound and surrounding soft tissues. RESULTS AND DISCUSSION: US raised the suspicion of in-transit or satellite metastases in 63 patients. A total of 95 lesions were identified. Average lesion diameter was 0.7 mm, and only four were larger than 1 cm. All suspected lesions were confirmed by surgery, follow-up or US-guided fine-needle aspiration (FNA) with 22-gauge needles using a freehand technique and exploiting the capillarity principle. In this series, there were apparently no false positive or false negative US results although inclusion criteria precluded correct evaluation of possible false negatives. Minimum lesion diameter allowing sonographic detection appears to be around 0.4 mm. US features of in-transit metastases have been well documented. They usually appear as solid lesions, hypoechoic relative to the surrounding subcutaneous fat and with relatively well-defined and regular contours and good US transmission. Internal structure is fairly homogeneous, and sometimes millimetresized fluid areas can be appreciated inside. Larger metastatic lesions may exhibit internal vascular signals at power Doppler imaging. These findings in dermatological sonography are almost exclusive of metastases but may also be seen in glomangioma, which, however, has intense intralesional vascularity. US-guided FNA plays an important role in diagnosis of metastases from malignant melanoma. Of the 32 nodules that were cytologically sampled, a definitive or most probable diagnosis of metastasis was made for nodules with a mean diameter of 0.7 mm (minimum 0.5 mm).
CONCLUSIONS: Sonography of soft tissues surrounding the original site of a malignant melanoma should be more widely used and associated with US-guided FNA biopsy.