Sonographic Characteristics of Apocrine Nodular Hidradenoma of the Skin.

Nodular hidradenomas are benign sweat gland-derived tumors that can produce clinical and dermatoscopic misdiagnoses. Histologically, these tumors can be classified into eccrine and apocrine subtypes. We present the sonographic characteristics of 6 cases of apocrine nodular hidradenomas, which, to our knowledge, is so far the largest series reported. A detailed sonographic analysis included layers, body location, shape, diameters, echostructure patterns, and vascularity. Two sonographic signs not previously reported in these or other common dermatologic lesions were detected: "snow falling" and "fluid-fluid level." The sonographic characteristics of apocrine nodular hidradenomas can support their earlier and more precise diagnosis.