High-frequency ultrasound features of cutaneous hidrocystoma: a case series with imaging-pathology correlation.

Background: Cutaneous hidrocystoma is an uncommon benign cystic lesion of sweat gland origin that frequently presents diagnostic challenges. While clinical examination remains the first-line diagnostic approach, with dermoscopy increasingly used in dermatology practice, high-frequency ultrasound (HFUS) may provide additional valuable information for lesion characterization and surgical planning. However, systematic characterization of HFUS features in hidrocystoma remains limited. This study aimed to describe the sonographic features of pathologically confirmed cutaneous hidrocystoma, correlate these findings with histopathologic features, and summarize the potential role of HFUS in preoperative lesion localization and differential diagnostic assessment. Methods: Eleven patients with pathologically confirmed cutaneous hidrocystoma were analysed. All patients underwent clinical examination by dermatologists prior to ultrasound evaluation. Ultrasound examinations were performed by two board-certified radiologists with more than 10 years of experience in superficial soft-tissue imaging, using high-frequency linear transducers. Lesion location, size, morphology, margin, internal echogenicity, vascularity, and relationship to adjacent structures were systematically evaluated and correlated with histopathologic findings. Preoperative ultrasound findings were compared with postoperative histopathologic results. Results: Eleven lesions were identified in 11 patients (6 men and 5 women; age range, 27-71 years; mean age, 48.0 years). Eight lesions were located in the head and neck region. Most lesions measured less than 1.5 cm (10/11, 90.9%). All lesions were located within the dermis or superficial subcutaneous layer. Sonographic appearances were variable: heterogeneous echogenicity (36.4%), anechoic cystic features (27.3%), homogeneously hypoechoic (18.2%), and hypoechoic with papillary projections (18.2%). Blood flow signals were detected in 2 lesions (18.2%): one exhibited minimal vascularity, whereas the other demonstrated prominent peripheral vascularity with a circumferential encasing pattern. Preoperative ultrasound interpretations included cystic lesion (3 cases), epidermoid cyst (4 cases), hemangioma (2 cases), and hypoechoic nodule (2 cases). None of the lesions was interpreted as hidrocystoma on preoperative ultrasound. Conclusion: Although HFUS features of cutaneous hidrocystoma show certain patterns, they overlap with atypical epidermoid cysts and hemangiomas, limiting definitive preoperative diagnosis. Nevertheless, HFUS allows precise delineation of lesion depth, internal architecture, and vascular relationships, thereby facilitating accurate localization, narrowing the differential diagnosis, and supporting individualized surgical planning.