We report a case of a subsynovial epidermal inclusion cyst in a 47-year-old woman with a painful spontaneous swelling of the right knee and a 2-year history of puncture and arthroscopy. Epidermal inclusion cysts are one of the most common benign subcutaneous tumours. Very rarely, they are located in an articulation and can cause an inflammatory reaction when rupture occurs. Simple surgical excision is the preferred therapy. The main goal of this case report is to include the possibility of an intra-articular epidermal inclusion cyst into the differential when imaging shows an intra-articular structure, and more so if there is a history of trauma, intra-articular puncture or arthroscopy.

中文翻译：

---

膝下滑膜表皮包涵囊肿

我们报告了一名47岁妇女滑膜下皮下包涵囊肿的病例，右膝疼痛自发肿胀，穿刺和关节镜检查史为2年。表皮包涵囊肿是最常见的良性皮下肿瘤之一。它们很少位于关节处，并在破裂时会引起炎症反应。简单的手术切除是首选治疗方法。该病例报告的主要目标是，当影像学显示关节内结构时，将关节内表皮包涵囊肿包括在内，如果有外伤，关节内穿刺或关节镜检查史则更是如此。