The Collaborative International Dictionary of English v.0.48:
Lithiasis \Li*thi"a*sis\ (l[i^]*th[imac]"[.a]*s[i^]s), n. [NL., fr. Gr. liqi`asis, fr. li`qos stone.] (Med.) The formation of stony concretions or calculi in any part of the body, especially in the bladder and urinary passages. --Dunglison. [1913 Webster]WordNet (r) 3.0 (2006):
lithiasis n 1: the formation of stones (calculi) in an internal organ