Principles of high-frequency ultrasonography for investigation of skin pathology

Ultrasonography is a valuable diagnostic tool widely used in medicine. During the last three decades, this non-invasive skin imaging method has been extended to dermatology. High-frequency ultrasonography with higher than 20 MHz scanners is well-established for measuring tumour thickness and skin thickness when treating inflammatory skin diseases such as scleroderma or psoriasis. High-frequency ultrasonography has become extremely helpful for the preoperative assessment of skin melanoma. The correlation between ultrasonic and histological measurements of melanomas thickness is significantly similarly good using transducers of 20, 75 or 100 MHz frequency (r range from 0.895 to 0.99) and better compared with transducers of 7.5 MHz frequency (r = 0.76). The preoperative sonographically estimated thickness of skin melanoma is sometimes overestimated, because of an underlying inflammatory infiltrate and other reasons. Assessment of skin melanoma thickness using transducers of 100 MHz frequency has better agreement with histology, compared with ultrasonography with 20 MHz transducers. However, the ultrasonic penetration depth is limited to 1.5 mm in case of 100 MHz. The newer ultrasonic techniques such as high-frequency ultrasonography and colour Doppler sonography could be used for assessment of the tumour vascularization and its metastatic potential. The wide variety of diagnostic information provided by high-frequency ultrasonography undoubtedly improves the management of oncological and inflammatory skin conditions and underlines its essential position in dermatological practice.