患者女， 21岁。于 1998年 9月 2日就诊。半年前左上臂外侧出现绿豆大小囊肿，无痒痛。皮损逐渐增大至 5分硬币大小，且压痛。无家族史。体检：各系统检查无异常。皮肤科检查：左上臂外侧可见 5分硬币大小囊肿 (图 1)，正常肤色，柔软有波动感。中心部分皮下隐约可见暗黑色物， Female patient, 21 years old. On September 2, 1998 for treatment. Six months ago, the emergence of mung bean-sized cyst on the outside of the left upper arm, no itching pain. Skin lesions gradually increased to 5 points coin size, and tenderness. No family history. Physical examination: no abnormalities in the system examination. Dermatology examination: the left upper arm can be seen 5 points coin size cysts (Figure 1), normal skin color, soft and volatile. The center part of subcutaneous darkly visible dark matter,