Proximal Epithelioid Sarcoma Mimicking Inguinal Inflammation.

Epithelioid sarcoma (ES) is an extremely rare sarcoma categorized into classic and proximal types. Proximal ES is characterized by its occurrence in older individuals, proximal locations, deep tissue involvement, and a tendency to be larger in size. We present a case of an extremely small proximal ES occurring in the inguinal region, which posed significant diagnostic challenges. Clinically, the lesion presented as a painful mass, and magnetic resonance imaging findings suggested lymphadenitis or other inflammatory lesions due to its small size and internal signal patterns. Despite being monitored, the mass showed progression, prompting an incisional biopsy that raised suspicion for ES. Positron emission tomography-computed tomography confirmed the absence of metastases, leading to wide excision. Pathological examination of the excised specimen confirmed proximal ES with negative margins. In this case, characteristic features of proximal ES were scarcely observed, and imaging findings were not distinctive, likely due to the small size of the lesion. Furthermore, the broad differential diagnoses for inguinal masses necessitate careful attention during diagnosis. For sarcomas and tumors in general, reliance solely on clinical and imaging findings can lead to diagnostic pitfalls, emphasizing the importance of active pathological evaluation through biopsy.