Although we tend to suspect torsion only in cases where there is ovarian enlargement, cyst, etc., there are a number of studies that show these are not reliable (sensitive or specific) indicators of torsion. Radiology reports often seem to hedge and note that ovarian torsion is a clinical diagnosis because the test characteristics of ultrasound are not that great even when you include flow, adnexal size, free fluid, and other factors in combination.
Children (<15 years old) are at greater risk of torsing normal ovaries (up to 50% of torsion cases), but even in women of childbearing age 8-19% of cases are associated with normal ovaries. Doppler flow has demonstrated great sensitivity and specificity for torsion by some authors but was much less valuable in this retrospective study.
In this recent study, abnormal ovarian location, abnormal flow and free fluid were the best predictors of torsion; ovarian mass or cyst actually didn’t help rule in or out the diagnosis.
Bottom line: normal ovaries do not rule out torsion. Doppler flow may not be sensitive or specific enough either. So use (dare we say it?) clinical judgement.