Focal Area of Low T2 Signal on MRI Scans in a Heterogeneous Uterine Leiomyoma Does Not Exclude the Possibility of Malignancy: A Report of Two Cases.

Background: Uterine sarcomas are uncommon malignant tumors with a grim prognosis, accounting for less than 1% of all gynecologic malignancies. Radiological series often include a limited number of patients, and diagnostic approaches can vary. While the presence of low T2 signal intensity in leiomyomas on MRI has been proposed as a criterion to exclude sarcoma, exceptions to this rule exist. We present two cases that challenge this notion. Case reports: The first patient was a 48-year-old woman presenting with metrorrhagia. MRI revealed a large intramural leiomyoma characterized by extensive hypointensity on T2-weighted imaging (T2WI) and a small intraleiomyoma focus with intermediate signal intensity. Histopathological examination confirmed leiomyosarcoma. The second patient was a 51-year-old woman presenting with menometrorrhagia. MRI showed a subserosal myoma with zones of T2WI hypointensity interspersed with a region of intermediate signal intensity. Histopathological examination confirmed low-grade endometrial stromal sarcoma. In both cases, diffusion-weighted imaging (DWI) revealed an intratumoral zone of restricted diffusion, with an apparent diffusion coefficient (ADC) value ≤ 0.86 × 10-3 mm2/s. Conclusion: MRI is crucial for distinguishing leiomyomas from sarcomas. We propose combining T2WI and DWI with ADC for this purpose, noting limitations in each sequence's reliability. Suggestive MRI criteria for malignancy in sarcomas are identified, emphasizing the need for comprehensive imaging analysis. In characterizing uterine smooth muscle tumors, particularly when analyzing leiomyoma variants, DWI emerges as the dominant sequence, with T2WI serving as a secondary sequence. ADC values aid in histopathological hypothesis, but caution is warranted due to overlap with benign lesions. This approach may refine preoperative diagnosis and guide therapeutic management.