noun
cyst
Medical term for a fluid-filled sac in the body. Often used in compound words like 卵巣嚢腫 (ovarian cyst).
See also: 嚢胞
超音波検査で卵巣に嚢腫が見つかった。
An ultrasound found a cyst on the ovary.
歯根嚢腫は歯の根元にできる嚢腫です。
A radicular cyst is a cyst that forms at the root of a tooth.
Both mean 'cyst', but 嚢胞 is more common in modern medical terminology, while 嚢腫 is somewhat older or more specific to certain types of cysts.
From 嚢 (sac) + 腫 (swelling/tumor). The exact historical derivation is uncertain; the spelling is conventionally associated with the medical meaning.