The term "pelvic phlebolith" refers to a small mass that grows in the wall of a vein in the pelvic region. Pelvic phleboliths resemble an accretion of lime or calcium, and they are generally harmless. Since they do not ordinarily manifest symptoms, it is common for them to be detected only incidentally to a pelvic X-ray, according to Reference.com.
Pelvic phleboliths are generally of no clinical importance, as they are not diagnostic of any medical conditions apart from hemangiomas, which are themselves harmless growths inside the blood vessels, and do not cause the patient discomfort, according to Wikipedia. When phleboliths do show up on an X-ray, they can be difficult to identify properly. This is especially the case for pelvic phleboliths, as they can easily be mistaken for kidney stones or other calcified masses. Phleboliths are more common in the lower regions of the body, which makes the confusion with kidney stones lodged in the ureters even more likely.
Pelvic phleboliths are very common. Wikipedia states that phleboliths in the pelvic region occur among 1 in 3 men and half of all women, with the incidence rising with the patient's age. Phleboliths occur outside of the pelvic region less commonly--around 2% of the time.