Attending in Emergency Department(AED)

Recently I encounter a case of 48 y/o female c/o epigastric pain for 1 day. CBC and SMA and UA are normal and KUB showed no ileus or free air. Keto(NSAID) 1 amp IV is given and stay in ED overnight. When I saw the patient and place the ultrasound proble over the abd, there is a large hypodense mass seen on the screen, especially over lower abd. So I tell the patient to urinate in order to rule out urinary retention. But after the patient urinates, ultrasound showed the image of a large hypoechoic mass in lower abd to mid-abd above umbilicus. There is no ascites seen in Morrison's pouch and this is not stomach distension since I press the mass, patient didn't vomit at all. All in my mind is a cystic lesion but origion from where. Woman of 48, may be from ovary.
After consultation with GYN, they admit the patient due to a huge pelvic mass from ultrasound findings. Exploratory laparotomy 2 days later showed a large right ovary mass and oophorectomy had done. Retrospectively when I review the KUB , I can see there is a soft tissue mass density in pelvis. So careful examination and careful reading of X ray is necessary. Ultrasound still play an important role in differential diagnosis of acute abdomen.