"在十分罕见的情况下" 这句话用英文怎么说吗?

在十分罕见的情况下
In very rare cases

塔特玛的情况十分罕见，她的寄生双胞胎在她出生后就停止生长了。
Lakshmi has an extremely rare condition in which her parasitic twins stopped developing after birth.
在目前的系统中，接受基于信用发行的国家货币作为主要的国际储备货币这种情况，从历史上来看，是十分罕见的。
The acceptance of credit-based national currencies as major international reserve currencies, as is the case in the current system, is a rare special case in history.
那样当然也可以，不过这样的补偿贸易十分罕见，而且在我们这种情况下根本行不通。
That's certainly another possibility, but it is rather rare in compensation trade and simply won't work in our case.

under very rare circumstances.

In very rare circumstances

under rare condition