在原发性纵膈肿瘤中,胸腺囊肿是比较少见的,迄今我们收集国内文献报告的共28例(1—7),病因不清,通常认为是炎症、瘤性或先天性囊肿等。本文报告我院1987年收治的一例巨大胸腺囊肿。病程历经12年,手术切除时囊肿的含液量达3000余毫升,巨大程度实属罕见。我们对患者进行了家系调查及染色体检查,该患者发生在挠侧多指畸型家族中,从而阐述了胸腺囊肿与遗传性多指畸型有一定关系. In primary mediastinal tumors, thymic cysts are relatively rare. So far we have collected a total of 28 cases (1-7) reported in the domestic literature. The etiology is unclear and is usually considered to be inflammation, neoplastic or congenital cysts. This article reports a case of a huge thymic cyst in our hospital in 1987. After 12 years of disease, the cyst fluid content during surgical resection was more than 3,000 milliliters, which is extremely rare. We conducted a family survey and chromosome examination of the patient. The patient developed polymorphisms in the fibular polydactyly, thus explicating the relationship between thymic cyst and hereditary polydactylia.