In addition to tumor size, the French Federation of Cancer Centers histologic grading system is the most important prognostic factor in soft-tissue sarcoma (STS). The French Federation of Cancer Centers grading system considers tumor differentiation, mitotic activity, and necrosis (1). Several studies have validated its predictive value for local recurrence-free survival, metastasis-free survival, and overall survival (2-5). Because anthracycline-based neoadjuvant chemotherapy improves prognosis in patients with locally advanced deep-seated grade III STS, grade is routinely assessed to support its indication (6-9). Grade was historically validated on complete surgical specimens; however, imaging-guided core-needle biopsies have now become standard in the diagnosis of STS (10,11). Therefore, due to tumor heterogeneity, the initial grading performed on biopsy samples may underestimate the final grade rendered on the surgical specimen (12-14).Two approaches could be used to limit grade underestimation. The first approach is the identification of high-grade areas at imaging to guide biopsies. Previous studies have investigated the relationship between imaging features and grade by using conventional MRI, radiomics analysis of diffusion-weighted imaging, and fluorine 18 fluorodeoxyglucose PET/CT; these studies have identified associations between glycolytic metabolism, tumor heterogeneity, growth pattern, and grade (14-19). However, direct voxel-to-voxel comparisons of histologic grades and potential imaging features are lacking. In practice, many patients who present with a soft-tissue mass are referred to sarcoma reference centers with a conventional MRI examination already performed out of the center. Furthermore, to optimize the biopsy, radiologists purposely avoid targeting necrotic areas, which may lead to an underestimation of the amount of necrosis.

A 27-year-old woman underwent a first vaginal delivery at our institution. She returned four days after delivery, presenting with abdominal pain and an unexplained drop in her hemoglobin value, without external bleeding. The initial computed tomography abdominal scan revealed an isolated diffuse hemoperitoneum. A laparoscopy did not find the cause of bleeding. A second computed tomography scan, performed 15 days later, revealed hemoperitoneum associated with a false aneurysm of the right uterine artery. Treatment consisted of embolization of the uterine arteries, with clinical success. False aneurysms are a rare cause of intra-abdominal non-exteriorized bleeding in late post-partum hemorrhage.