患者因为肾结石疼痛难忍而住院。

The patient was hospitalized due to severe pain caused by a kidney calculus.

calculus 是名词，来自拉丁语，原意是"小石子"。在医学上特指体内形成的硬质矿物沉积物，即"结石"。 kidney calculus 指肾脏中形成的结石，也就是"肾结石"。