Case report: retentive fibroid tumor of the ileocecal region during pregnancy.

Background: Desmoid type fibromatosis (DTF) is a rare, non-metastasizing but locally invasive intermediate soft tissue tumor. With an annual incidence of 2-4 per million, it is particularly rare during pregnancy. The particularity of this case is that the patient is pregnant, 14 weeks gestation, placenta previa, and a large mass is found in the abdominal pelvic cavity. The patient requests to terminate the pregnancy and remove the abdominal pelvic cavity mass. The large mass originates from ileocecal area, which is extremely rare and can be an excellent supplement to the literature. Case Description: A 32-year-old woman found out she was pregnant 6 weeks after her last period and had no discomfort. At 14 weeks of pregnancy, ultrasound and magnetic resonance imaging (MRI) showed: there was a huge hypoechoic mass above the uterus, accompanied by connecting blood vessels. It was misdiagnosed as uterine fibroids. Through multidisciplinary team (MDT) assessment, formulated a surgical plan. The patient and her family signed the informed consent form and decided to undergo the surgery. Following termination of pregnancy, exploratory laparotomy uncovered a mass originating from the ileocecal region, with vascular connections to the uterine surface but no significant adhesions. The patient underwent successful tumor resection with ileocecal resection. Histopathological examination of the mass confirmed a diagnosis of DTF, characterized by spindle cells without significant atypia. Immunohistochemistry was pivotal, showing nuclear positivity for β-catenin and a Ki-67 index of <10%, while being negative for markers like CD117, effectively ruling out gastrointestinal stromal tumor (GIST). Through this case, we recognize that there is a vascular connection between the tumor and the uterus, and its origin is not necessarily the uterus; it could be of intestinal origin. The uniqueness of this case lies in: a huge mass was found in the pregnant woman's abdominal and pelvic cavity, without intestinal obstruction, and there is a vascular connection with the uterus. Conclusions: This case underscores the diagnostic difficulty of DTF. A clear diagnosis depends on postoperative pathological examination and immunohistochemistry, and multidisciplinary collaboration is of vital importance.