Responsa for Niddah 41:41

L has a wart in her vagina which bleeds during copulation and even when touched by the "examining rag". I am inclined to believe that L is ritually clean since we assume that her blood comes from the wart and not from the interior of the womb. During her regular period (of menstruation), if she definitely feels that the blood comes from the wart, she is ritually clean; otherwise she is unclean. At other times she is ritually clean even when she does not definitely feel that the blood comes from the wart. She can recognize the menses by a greater flow of blood than that which usually comes from the wart. At her menstruation period she must count the same number of days as hitherto. Moreover, knowing exactly where the wart is situated, she should be able to manipulate the "examining rag" in such a way as to discover whether there be present any menstrual blood.
SOURCES: Am II, 53; cf. Pr. 626; Mord. Niddah, 735. Cf. Maharil, Responsa 173.