Sonographic appearance of sebaceous cysts. Our experience and a review of the literature.

Sebaceous cysts are benign enveloped nodules resulting from an obstruction of a hair follicle. Although they are very common, differential diagnosis is not obvious and may include many diseases. Ultrasound examination with high frequency probes, in the hands of a skilled operator, is the gold standard for noninvasive evaluation of these diseases. The aim of our study was to describe sonographic patterns found in our experience with high frequency probes. We decided to reevaluate the sonographic appearance of the last 100 patients with sebaceous cysts that were under our observation through conducting a retrospective study. All lesions were examined by a skilled radiologist with an Esaote MyLab 70 XVG ultrasound unit and a dedicated 18 MHz linear probe, sometimes supplemented by 20 MHz. In these skin lesions, we evaluated morphology, size, vascularity, and especially the visibility of skin pores, a characteristic of sebaceous cysts. We found 118 lesions that were mostly located on the trunk. In the majority of cases, the skin lesions had an oval-shaped morphology - 114 (96.6%) - and were hypoechoic in appearance -108 (91.5%). In 60 (50.8%) cases, the skin lesions showed a homogeneous appearance, known as "pseudotestis". The average ultrasound examines with very high frequency probes allowed to evidence skin pores. Our retrospective study on higher frequency probes confirms the data in literature regarding the diagnosis of sebaceous cysts, demonstrating the high incidence and clinical significance of evidence of the so-called epidermal punctum.