Mucous cyst - 黏液囊腫 https://en.wikipedia.org/wiki/Mucocele
黏液囊腫 (Mucous cyst) 是一種良性神經節囊腫,通常發生在遠端指間關節。

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References Digital Mucous Cyst 32644518 
NIH
Digital mucous cysts 是手上常見的一種囊腫。 Ganglion 是一種軟組織腫瘤,常見於關節或肌腱附近。 Digital mucous cyst 特別是從遠端指間關節(DIP 關節)的背面發展而來。這些囊腫通常與 DIP 關節的骨關節炎一起存在。
Digital mucous cysts are a type of ganglion commonly found on the hand. A ganglion is a soft tissue tumor that is found next to a joint or tendon. A digital mucous cyst is a ganglion that arises from the dorsum of the distal interphalangeal joint (DIP joint). Digital mucous cysts commonly have an association with underlying DIP joint osteoarthritis.