text: i have trace amount of ascites seen in the pelvis. how did i get that? i was also told that my uterus is septate ascites is defined as an excessive amount of fluid built up within the peritoneal cavity. both the abdominal organs and the abdomen itself are lined with membranes called the peritoneum. between these two linings is a space referred to as the peritoneal cavity. in pathological conditions that result in edema, or excessive fluid accumulation in bodily tissues, fluid can build up in the peritoneal cavity.   a septate uterus is a uterus with a dividing wall of tissue (septum) within the uterine cavity. it can be treated with surgery if the tissue is thick, but if the tissue is thin it usually poses no problem during pregnancy. as for what caused your condition, ask your doctor.  he or she is the best source for your medical questions.  ascites, in itself, is not a disease, but rather a symptom of several other pathological conditions.