Here are four papers on ovarian torsion. If you suspect torsion clinically, do NOT be reassured by normal flow on USN. Only the last paper (12 years old) showed a high sensitivity of ultrasound doppler flow for torsion. The other findings matter!

Diagnostic Efficacy of Sonography for Diagnosis of Ovarian Torsion (2014)

323 subjects. The ultrasound correctly diagnosed 72.1% of ovarian torsion and missed 27.9% of them (false negatives)

Ovarian torsion: Case-control study comparing the sensitivity and specificity of ultrasonography and computed tomography for diagnosis in the emergency department (2014)

20 cases, 20 controls. Pelvic US for ovarian torsion was 80.0% sensitive (95% CI, 58.4-91.9%) and 95.0% specific (95% CI, 76.4-99.1%) for reader 1, while 80.0% sensitive (95% CI, 58.4-91.9%) and 85.0% specific (95% CI, 64.0-95.0%) for reader 2.

Diagnosis of Ovarian Torsion: Is It Time to Forget About Doppler? (2018)

55 cases of surgically proven torsion, 48 controls. Sixty-one percent of right ovarian torsion case and 27% of left ovarian torsion cases had normal Doppler flow. Presence of ovarian cysts was significantly associated with torsion. Sensitivity of ultrasound was 70% and specificity was 87%.

Doppler studies of the ovarian venous blood flow in the diagnosis of adnexal torsion (2009)

One hundred and ninety-nine patients presented with adnexal mass and intermittent lower abdominal pain. Sensitivity and specificity of tissue edema, absence of intra-ovarian vascularity, absence of arterial flow, and absence or abnormal venous flow in the diagnosis of adnexal torsion were: 21% and 100%, 52% and 91%, 76% and 99%, and 100% and 97%, respectively. All patients with adnexal torsion had absent flow or abnormal flow pattern in the ovarian vein. In 13 patients, the only abnormality was absent or abnormal ovarian venous flow with normal gray-scale US appearance and normal arterial blood flow. Of these 13 patients, 8 (62%) had adnexal torsion or subtorsion.

TL;DR

1. Ovarian Torsion is a clinical diagnosis. Ultrasound is NOT 100% sensitive.

2. Read the USN report, Just like a cardiac cath*, normal must really mean normal. If you can’t visualize one ovary, or have normal ovarian flow but a large cyst, or have edema, etc, that is NOT a normal pelvic ultrasound.

* A cath report that has 50% blockage in 2 vessels is not “normal” or “clean”! Caths with absence of a lesion that requires PCI (stent) can still have abnormalities that are very important. Remember, the 50% coronary plaques are the most likely to be unstable and rupture.