Divergent Intralesional Enhancement Kinetics in a Primary Ovarian Leiomyoma on Dual-Layer Spectral CT: A Case Report

Background and Clinical Significance: Indeterminate solid adnexal masses can remain difficult to characterize on conventional CT. Dual-layer spectral CT provides iodine concentration (IC), effective atomic number (Zeff), and electron density relative to water (EDW) from the same acquisition. We report a histopathologically confirmed primary ovarian leiomyoma and describe its regional multiphasic spectral behavior. Case Presentation: A 37-year-old woman presented with an O-RADS 4 solid right adnexal mass. Retrospective analysis sampled two enhancement-defined intralesional compartments across true noncontrast (TNC), arterial, venous, and delayed phases. On TNC images, ROI-A and ROI-B showed closely similar Zeff (7.39 vs. 7.37) and EDW (103.8% vs. 103.9%). ROI-A showed intense arterial enhancement (102.2 HU; IC 2.95 mg/mL; Zeff 8.78) followed by decline, whereas ROI-B showed low early enhancement and marked delayed fill-in, with delayed values slightly exceeding ROI-A (83.8 vs. 71.3 HU; IC 1.74 vs. 1.54 mg/mL; Zeff 8.25 vs. 8.16). Initial histopathology suggested fibroma; immunohistochemistry established ovarian leiomyoma. Conclusions: The two enhancement-defined compartments showed closely similar baseline spectral measurements but divergent postcontrast behavior. EDW demonstrated substantially lower-amplitude phase-related changes than IC and Zeff. These findings are descriptive and do not establish a diagnostic spectral signature or histologic specificity. When multiphasic dual-layer spectral CT has already been clinically acquired, regional spectral analysis may provide quantitative characterization of intralesional enhancement heterogeneity. In this case, however, spectral CT did not establish the diagnosis or alter management, and definitive diagnosis remained dependent on histopathology and immunohistochemistry.