Re: Fetal magnetic resonance imaging: luxury or necessity?

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Re: Fetal magnetic resonance imaging: luxury or necessity?

I was unpleasantly surprised by the recent Editorial article, ‘Fetal magnetic resonance imaging: luxury or necessity?’1. The authors may have misunderstood the intent of the society (ISUOG) in dedicating two sessions at the 2005 World Congress to magnetic resonance imaging (MRI). I think it was to demonstrate what MRI is capable of, in terms of adding to fetal diagnosis. Unfortunately, the authors overstated the facts by referring to: ‘the increasingly important role of MRI in our practices’, which in many senses is misleading. The authors appeared as self-appointed judges of the value of MRI in obstetrics, implying unproven facts.

I attended numerous lectures in which the lecturer tried to convince the audience that MRI does better than ultrasound. In the side-by-side images, the ultrasound pictures were usually of a seriously substandard quality: an unfair comparison! Unfortunately, in many cases MRI had been substituted for a poor-quality ultrasound examination that had been performed using the wrong transducer, the wrong scanning route and incorrect settings. It is no wonder that the MR images appeared to be better. If, in the same lectures, MRI and ultrasound images of similar quality had been used to show the same pathology, it would have been unclear why MRI (the more expensive and cumbersome modality) had been used, when the simple, less expensive ultrasound test would have provided the same diagnosis.

It is unfortunate that some obstetricians (generalists and maternal–fetal medicine specialists) reach for the referral-to-MRI slip too fast, instead of opting for the simpler, less expensive, and readily available approach of ultrasound. They may be under the false impression (created by the indiscriminate push to use MRI in cases of suspected fetal anomalies) that it will serve the patient better.

We have seen several patients referred for a second opinion because of a suspected fetal anomaly, who have already undergone fetal MRI, the findings of which were inconclusive or resulted in an incorrect diagnosis. Sometimes, patients bring with them MRI films taken at 16 or 18 weeks. In order to scrutinize detail so early, you need a magnifying glass; the resolution of such MRI pictures at these early gestational ages is well below that obtained using good high-frequency transvaginal transducers. There is little doubt that younger fetuses can be better imaged by transabdominal or transvaginal sonography than they can with MRI.

Perhaps I lack the analytical ability to properly evaluate the Editorial in question, with respect to all fetal organs for which the authors claim the diagnostic importance of MRI. I will only mention the section on the fetal central nervous system (CNS). My question—at the outset—is this: did the authors read carefully the quoted articles (7, 12–26 in their reference list)? I read through them and, with the exception of the articles on biometry (13, 15 and 18 from the Editorial), all quoted articles are dedicated to cortical maturation, to pathologies of the fetal brain acquired late in pregnancy, or to spectroscopy performed at 40–41 weeks. If indeed there were MRI scans of cases performed prior to 20–22 weeks, they were merely confirmatory of the ultrasound images, with little or no additional value.

Even if MRI is useful to diagnose fetal brain pathology, this article is premature to advertize its presumed virtues. The reasons for this, among others, are:

  • 1.As it stands today MRI adds precious little to evaluation of the fetal CNS prior to 20–22 weeks, when it is most important to establish an accurate diagnosis.
  • 2.There are few centers that engage in fetal MRI in general and in examining the fetal CNS in particular. This means limited and scattered availability.
  • 3.There are even fewer qualified radiologists who have the knowledge to correctly read MR images. The field may grow in the future; however, at this time false results may obscure the true value of MRI.
  • 4.Not infrequently, when MRI is ordered for a suspected fetal brain anomaly, the reports suggest that a more detailed ultrasound evaluation is required.

Despite the disclaimers in the Introduction and Conclusion sections of the Editorial, the content of the CNS portion is misleading. The real value of MRI, as it transpires from the literature, is its undisputed value after the first half of the pregnancy, in particular in heterotopias and gyral disorders as well as white matter lesions. What would be useful is if the obstetrician and perinatologist knew when to ask for a targeted ultrasound evaluation of the fetal CNS and when to refer their patients for an MRI study. Even more important is for the MRI center to have the expertise to provide an accurate, knowledgeable evaluation of the fetal brain.

Finally, the authors did not answer their own question, posed in the title of their Editorial. Let me do this for them: at this time, at least for the fetal CNS, not only the initial but also further targeted fetal neuroimaging belongs in the ultrasound laboratory. It seems that MRI is still generally an expensive luxury that is not widely available and is only sporadically a real necessity. Now is not the time to replace ‘ultrasound’ by 'imaging in the name of our Society.

I. Timor-Tritsch*, * 550 First Avenue, NBV-9N26, New York, NY 10016, USA

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