Ovarian Masses - Part 6 - 3
Are Resistive Indices the Answer to the Question
Is this lesion Malignant?
Are Resistive Indices the Answer to the Question
Is this lesion Malignant?
how low is a low resistance ri?
- Most literature identifies an RI < 0.4 as abnormally low
do malignant neoplasms have low ri's
- Yes, studies have consistently shown that malignant lesions have lower mean RI's than benign lesions and this difference is statistically significant.
- It is important to remember that statistical significance only means that the result is unlikely to have occurred by chance, it does not mean that the result is clinically useful!
So, are ri's helpful in triaging malignant vs. benign lesions?
- Lesion definitely benign based on morphology?
- We've already said that morphology is nearly 100% accurate in diagnosing benign lesions
- Lesion suspicious for malignancy based on morphology
- We've said that we tend to overcall lesions malignant when we think they are benign, so, the question is: Will the "absence of a low RI" make us comfortable calling something benign?
- Let's look at some cases:
- All three of these are cancer and all three, by our morphologic criteria should be removed.
- None had RI < 0.4
what is the problem here? - verification bias
The issue with research showing that low RI's are important suffer from the problem of "the primary diagnosis is driving the second order test"
- What this means is that based on morphology, you are already convinced that the lesion is malignant, so you will tend to search and search until you find the RI that verifies your primary assumption
- So, in this case, we see that we find multiple RI's > 0.4, however, we are so convinced based on morphology that it is malignant that we keep searching until we finally find that RI < 0.4