Anal swelling before menstruation may be caused by pelvic congestion, neuroendocrine hormone causes. 1. Pelvic congestion: the most important is the menstrual period pelvic congestion caused by the menstrual period, the entire pelvic cavity in the menstrual period in the congestion is very obvious, because the menstrual period in the endometrium is in the erosion of the endometrial lining, shedding of the period, so that the entire pelvis is a feeling of bloating. Not only the anus has a feeling of swelling, may be the entire pelvis, including the urethra, the entire mouth of the uterus always feel a feeling of swelling, and even the abdomen also has a feeling of swelling. 2. Neuroendocrine hormone reasons: it may be related to the secretion of neuroendocrine hormones, because women’s menstruation itself is the hormones secreted by the ovaries, as well as the neuroendocrine system hormones under the control and regulation of the occurrence of the situation, so it will also lead to pre-menstrual anal distension. This symptom alone is not enough to diagnose the disease, do not rule out that it is caused by other factors. It is recommended that patients go to the hospital as soon as possible for examination, and after the doctor clarifies the cause of the disease, targeted treatment will be given to avoid delaying the condition.