Ultrasound findings of endocrine mucin-producing sweat gland carcinoma mimicking epidermal cysts: A case series and diagnostic challenges.

Endocrine mucin-producing sweat gland carcinoma (EMPSGC) is an uncommon, low-grade, malignant tumor that predominantly affects older patients and is often located around the eyelids. Diagnosing EMPSGC is challenging because of its clinical and imaging similarities to benign lesions such as epidermal cysts. This report presents two cases of EMPSGC with ultrasound features resembling benign cystic lesions that were initially considered in the differential diagnosis. For both cases, ultrasound imaging revealed hypoechoic masses with posterior acoustic enhancement and peritumoral vascularity, which are frequently associated with epidermal cysts. However, a histopathological analysis confirmed the diagnosis of EMPSGC demonstrating solid and papillary structures with mucin pools and neuroendocrine differentiation. These cases highlight the potential for misdiagnosis using preoperative imaging because ultrasound can obscure malignancy. Enhanced posterior echoes likely stem from mucin deposits within the tumor, thus underscoring the need for an early biopsy and histological analysis when atypical findings are observed. Additionally, Doppler ultrasound detected a peritumoral blood flow, which may suggest malignancy; however, benign lesions may exhibit similar vascularity. Further accumulation of cases is necessary to determine whether peritumoral vascularity is a distinguishing characteristic of EMPSGC. This report emphasizes the importance of recognizing EMPSGC's mimicry of benign lesions on ultrasound, particularly in cosmetically sensitive areas. An accurate diagnosis of EMPSGC requires imaging, histopathology, and immunohistochemical staining because misinterpretation may delay appropriate treatment and increase the risk of recurrence.