Fig. 4. Decidual change of an ovarian endometriotic cyst at 16 weeks of gestation in a 33-year-old female.

A, B. Sagittal HASTE (A); sagittal T1WI (B). Small ovarian endometriotic cyst (arrowheads), hyperintense on T1WI (B), and shading on HASTE (A) are observed just behind the pregnant uterus. In the middle of the endometriotic cyst, decidual changes are observed as irregularly thickened soft tissue (white arrows). It shows hyperintensity on T2WI, similar to the placenta (black arrow) and low signal intensity on T1WI. C, D. Sagittal DWI (C); Sagittal ADC map soft tissues (D) showed hypointensity on DWI (arrow) and hyperintensity on the ADC map (arrow), indicating no diffusion restriction. Linear and broad-based appearances are also typical findings of decidual change. ADC = apparent diffusion coefficient, DWI = diffusion-weighted imaging, HASTE = half-Fourier single-shot turbo spin echo, WI = weighted image