Retroflexed Uterus. The uterus is flexed with the fundus (f) directed posteriorly toward the sacrum on this sagittal midline transbladder image. A retroflexed or retroverted uterus may be mistaken for a pelvic mass on both physical examination and US. The vagina is well seen with its hypoechoic muscular walls (long arrow) and echogenic mucosa (short arrow). c, cervix; e, endometrium.

http://www.msdlatinamerica.com/ebooks/FundamentalsofDiagnosticRadiology/sid454050.html