Which of the following is the COMMONEST cause of pyometra?

Pyometra refers to filling of the uterine cavity with pus. It occurs due to a blocked cervical canal in conditions such as cervical carcinoma or postmenopausal stenosis, it can also occur in senile endometritis, cancer of body of uterus, and puerperal endometritis.. In this condition, the cavity of distended uterus is filled with pus and the endometrium usually shows features of severe acute and chronic inflammation. Hematometra can result from atresia of the lower genital tract, vagina, and the cervix in an incomplete or complete vaginal septum. Clinical features can range from acute retention of urine to a case of primary amenorrhea with cyclical menstrual pain, it can also present as irregular menstrual bleeding or menorrhagia. Ref: Robboy's Pathology of the Female Reproductive Tract edited by Stanley J. Robboy, page 348. Textbook of Gynecology page 327.