[Echography applied in dermatologic diseases. A comparative preliminary study of the use of high-frequency transducers].

Ultrasonography (US) was first used in dermatology in 1979. During the last few years, US has evolved thanks to technological progress and its use has been on the increase, in dermatology, to study both localized and diffuse skin diseases. In this paper, the authors review and compare the results obtained with a 20 MHz transducer with those obtained with 7.5 MHz and 10 MHz transducers in the study of skin alterations. Three parameters were considered: lesion identification, spatial evaluation and US structure. Fifty-eight cases of localized and 48 of diffuse skin diseases were examined. The localized forms were benign in nature in 18 patients (3 nevi, 2 seborrheic keratoses, 3 ulcus cruris cases, 6 sebaceous and 2 liquid cysts). The other 40 patients had malignant neoplastic lesions (16 epitheliomas, 13 primitive melanomas, 1 metastatic melanoma, 8 lymphomas and 2 Kaposi's sarcomas). The 48 cases of diffuse conditions included 27 systemic sclerosis, 18 psoriasis and 3 lichen planus cases. The comparative analysis of the results obtained using the different types of transducers in the study of localized dermatoses showed no differences in lesion identification and in the depiction of their US features. On the other hand, the 20 MHz transducer was much more accurate than the others as regards the spatial evaluation of the lesions measurable in millimeters, whereas it poorly demonstrated the lesions > 1.5 cm. However, only the 20 MHz transducer could demonstrate the US features of diffuse conditions.