trigone
noun [ C ] anatomy specialized uk/ˈtraɪ.ɡəʊn/ us/ˈtraɪ.ɡoʊn/
（膀胱内壁的）三角区
a three-sided area on the inner surface of the bladder (= the bag where urine collects)
Since most of these tumours involve the trigone, they are rarely operable. 这些肿瘤大部分发生在膀胱内壁三角区，因此极少能做手术。