Objectives Uterine smooth muscle tumors of uncertain malignant potential (STUMP) represent a group of rare and challenging myometrial neoplasms. STUMPs that are followed by a recurrence are biologically low-grade leiomyosarcomas, but using current methods of analysis, this diagnosis cannot be made with certainty until a recurrence has developed. Our objective is to describe ultrasound findings in women with STUMP.

Methods We retrospectively evaluated preoperative sonographic data of patients with histopathological STUMP diagnosis between 2014 and 2018 in Turin S. Anna Hospital, a tertiary center. The tumors were characterized on the basis of ultrasound images and ultrasound reports using the terms and definitions of the Morphological Uterus Sonographic Assesment (MUSA) group.

Results Thirteen patients with STUMP (19 lesions, of which 17 pure STUMP and 2 STUMP with LMS associated) were identified. Using the MUSA terms and definitions most STUMP were poorly or moderately vascularized (69%) and almost all had both circumferential and intra-lesional flows (82%). Only three (16%) STUMP showed shadowing. Outline were well-defined in sixteen cases (84%). All STUMP had non-uniform echogenicity. Eleven (58%) STUMP were isoechoic, two (11%) hyperechoic and six (31%) had mixed echogenicity. Thirteen (68%) STUMP had microcystic anechoic areas. Over 30% of patients had multiple stumps and almost 80% associated myomas.

Conclusions The suspicion of STUMP is supported by the ultrasound finding of a single or multiple lesion, isoechoic or with mixed echogenicity, without shadowing, with regular borders, internal microcystic anechoic areas and vascularization from minimal to high both circumferential and intralesional.