“Perifollicular rim sign” in an enlarged ovary—an additional non-contrast CT finding in ovarian torsion

Purpose To look for the presence of “perifollicular rim sign” on non-contrast CT in surgically proven cases of ovarian or adnexal torsion. Methods A retrospective analysis of abdominopelvic non-contrast CT examinations in surgically proven cases of ovarian or adnexal torsion was conducted seeking the presence of “perifollicular rim sign” in torsed ovaries. “Perifollicular rim sign” was defined as a complete ring of perifollicular hyperdensity around ovarian follicles with an attenuation value of > 50 HU and thickness > 1–2 mm. A positive sign was equated to the presence of perifollicular hemorrhage. Pre-operative non-contrast CT was available in 7 out of the 39 ovarian or adnexal torsions included in our study. Results “Perifollicular rim sign” was present in 5 out of the 7 ovarian torsions on pre-operative non-contrast CT. MRI correlation was available in one patient. Ovarian enlargement (>4 cm) was present in all 7 cases. Conclusion In an appropriate clinical setting, presence of “perifollicular rim sign” in an enlarged ovary on non-contrast CT examination can be considered a useful additional sign for ovarian torsion.