Importance of sonography of the skin and subcutaneous tissue in the early diagnosis of melanoma in-transit metastasis with the presentation of two cases

Sonography is a non-invasive and inexpensive diagnostic imaging method, widely used in the field of internal medicine, especially oncology. Penetration into the tissue and organs varies depending on the frequency of the ultrasound applied. For studying internal organs and lymph nodes, a frequency range of 7.5–15 MHz is used, while for examining skin thickness, high-frequency scanners (HFUS) emitting waves at 20–100 MHz are applied [1]. The HFUS were first used in 1979. Since the 1980s, this method has constantly been improved and is now used for examining the thickness of skin lesions in different diseases – inflammatory diseases with fibrosis, psoriasis and lichen planus – and it is used to monitor the effectiveness of treating these conditions. High-frequency scaners are also used in cosmetic dermatology to assess skin damage [1, 2]. However, the most important use of sonography is in the diagnosis of cancer. While sonography cannot give a precise diagnosis of whether a skin lesion is malignant or not, nor specify the type of neoplasm, the test is nonetheless useful for assessing the depth of tumour infiltration. There was concordance between the results of ultrasound and histological tests in assessing the melanoma infiltration depth with the use of 20 MHz [3–6]. In the case of very thin metastatic melanomas, where the infiltration depth is less than 1 mm, it is necessary to apply a frequency of 100 MHz. The continued development of techniques using ultrasound, and in particular the introduction of colour Doppler sonography, which exposes the angiogenesis in a tumour, has also enabled the metastatic potential to be evaluated [7–9]