We discuss available modalities, indications for each, and emerging technologies in neonatal neuroimaging. We are joined by Michelle Machie, MD, Assistant Professor of Pediatrics and Neurology at UT Southwestern and Children’s Health Dallas.
Dr. Neeta Goli:
Welcome to Newborn News, a podcast where we discuss educational topics from medical professionals who care for newborns. I'm your host, Dr. Neeta Goli, a pediatrician in the UT Southwestern Newborn Nursery. Welcome back to the podcast. In today's episode, we'll be discussing indications for neonatal neuroimaging. We are recording remotely due to the ongoing COVID pandemic. We are joined today by Dr. Michelle Machie, Assistant Professor of Pediatrics and Neurology at UT Southwestern and Children's Health Dallas. Dr. Machie is fellowship trained in fetal and neonatal neurology, and her research has focused on the use of neuroimaging tools to predict and improve outcomes in infants at risk for abnormal neurodevelopment.
Dr. Michelle Machie:
Hello?
Dr. Neeta Goli:
Hi Dr. Machie, thanks for joining us today.
Dr. Michelle Machie:
Thank you so much for having me. I am really excited to join you and talk about one of my passions today, which is neonatal neuroimaging and its applications in the NICU and in outpatient settings.
Dr. Neeta Goli:
I'm so excited to learn from you today. So let's get started. There are certain clinical presentations in the nursery, which might require imaging of the brain and/or spine. So we can start with the brain first. So available imaging modalities include ultrasound, magnetic resonance imaging, x-ray, and computed tomography. Today we'll discuss when it's appropriate for each of these to be used in the nursery. So what might be indications that we need any neuroimaging in the first place?
Dr. Michelle Machie:
That's such a good question, and there are really so many growing indications to image the newborn brain. And the indications are expanding, basically as we're increasing our capacity to provide better, more extensive long-term follow-up for these babies, we're having a better understanding of what the utility of the early imaging can be. So I think for this question, the indications for neuroimaging, we can break it up a little bit and talk about the term infant first, and then discuss maybe more specific indications that are relevant to the preterm infant.
Dr. Michelle Machie:
So in the term infant, we really focus, or try to use a low threshold to assume that anything might be wrong with the brain. And the reason for that is that the manifestations of neurological disease in the infant can really be quite subtle. So of course, presentation clearly with hypoxic ischemic encephalopathy, or seizures, meningitis, microcephaly, macrocephaly, those are all really common indications for neuroimaging. And often present with clear manifestations of structural brain problems that will require neuroimaging.
Dr. Michelle Machie:
But there are more subtle findings as well, and things we look for on the exam to help guide us would be lethargy, increased or abnormally low muscle tone, the presence of dysmorphic features or multiple congenital anomalies, especially if an infant has multiple midline congenital anomalies affecting the heart or the kidneys, that can sometimes be reflected in the brain as well.
Dr. Michelle Machie:
We look for abnormal brainstem reflexes, the eye movements, the pupils. So those could all be indicators to image the brain. One pearl I'd like to provide is, we all check the Moro reflex. And it's a primitive reflex that we check in newborns and we expect it to be present and to disappear by a certain age, but it can also signify that there's a neurological problem, if it's asymmetric. So an asymmetric or even absent Moro reflex can be a sign that there might be an upper cervical spinal cord lesion or peripheral nerve lesion that's causing the muscles to not be able to respond. So we definitely want to use our full neurological exam and keep a really low threshold to say ... I say, "If you're even thinking about it, just go ahead and do it and look." Because the clinical findings can be so subtle. And so that's for the general term neonate.
Dr. Michelle Machie:
Specifically, indications for the preterm neonate, we really have a focus on early surveillance and detection protocols using head ultrasound to identify things like intraventricular hemorrhage or periventricular white matter injury, which are pathologies more specific to the preterm baby.
Dr. Michelle Machie:
And so my real takeaway for the preterm neonate is regarding the term-equivalent age MRI. And this is something that we are recommending more and more and is becoming more widely accepted nationally as a clear recommendation for the preterm infant born less than 30 weeks, given the risk for IVH, intraventricular hemorrhage or white matter lesions, that these babies should all be receiving a term-equivalent age MRI. And that would have the highest sensitivity and predictive value out of all the neuroimaging modalities that we have.
Dr. Neeta Goli:
Okay. And then, you mentioned some specific modalities. But what are the strengths and drawback of each of the imaging modalities that we have available to us?
Dr. Michelle Machie:
Yes. And I think that the strength or weakness for each of the modalities that we mentioned in the last question, it really comes down to basically your clinical setting, your practice location, and then what you have available for emergencies. So most centers, whether it's level one, two, three, four nursery NICU will have cranial ultrasound available. And cranial ultrasound or head ultrasound has been in wide use since the 1970s. It uses sound waves to detect differences. So we'll start there. And I think talk about the strengths for each one and the weaknesses for each one.
Dr. Michelle Machie:
For cranial ultrasound, it's pretty inexpensive. It's rapidly completed. It's a quick exam. It's widely available. Most centers have techs that are well-trained and can get good images and radiologists who can interpret. It's really great for identification of ventriculomegaly, cerebral edema, or hemorrhage in any infant with an open fontanelle. But the drawbacks, I would say, with cranial ultrasound are that it's really just not as sensitive as MRI. And it's not at good as determining the extent of the lesions. So I prefer that as more of a screening tool.
Dr. Michelle Machie:
Then I won't talk about single plane x-ray because that really doesn't have much utility as a neuro imaging modality. However, we do use CT scan or computed tomography, commonly. And CT scan uses basically it's a beam of x-rays that's rotating around the patient. And then the x-rays are absorbed by all the tissues it encounters. And so, it's really dependent upon the density of the tissue. So bone, being very dense, will be bright white on a CT scan and air, being a non-dense or hypodense tissue, will be black. And so CT scan is great for a lot of the same reasons as ultrasound. It's good for evaluating blood, calcium deposits, bony structures, and the ventricle. It's fairly inexpensive, especially compared to MRI. And it's pretty quick. But I would say the drawbacks for CT scan, unlike ultrasound, CT scan is not a bedside tool. So the baby has to be transported, which can be difficult if we have a critically ill infant. And it definitely requires the infant to be still, which can require sedation.
Dr. Michelle Machie:
I would say the biggest drawback, which we all think about with CT scan, is the exposure really to the high levels of radiation. And, ionizing radiation has really been associated with future development of malignancies yes, but also potential cognitive impairment. And so for me, I really worry about the risks and the effective dose of radiation and the developing newborn brain. So for that reason, I would really recommend use of CT scan more in settings, like traumatic head injury. If we need to understand whether a baby needs a neurosurgical intervention, or if there's concern for craniosynostosis more in the outpatient setting, and craniosynostosis is abnormal skull bone fusion, then CT scan would be the best modality.
Dr. Michelle Machie:
So we talked about head ultrasound, which I think is a great screening tool, CT scan, which I feel is more for emergency use in the neonate to avoid the risks that are associated with ionizing radiation. And then I saved the best for last. Please, excuse my bias.
Dr. Michelle Machie:
But, of course, I love MRI. And the MRI is magnetic resonance imaging. And it's basically just a big magnet. And we have different strength magnets we can use. Commonly most centers will have a 1.5 Tesla. We also have three Tesla MRI. And then in research, there is a new seven Tesla MRI, which is the strongest magnet available for research settings. Not yet, mostly, for clinical. How the MRI works is, it's basically the image contrast is based on properties of protons and water nuclei. And so it really is based on proton density of tissues.
Dr. Michelle Machie:
And the MRI, to be honest, just provides superb definition of the brain compared to ultrasound or CT scan. If there is an abnormality seen on the initial head ultrasound, ultimately we will typically end up recommending an MRI to confirm those findings. And then in contrast to CT scan, MRI does not require any radiation. And so we can use it really nicely for things like serial scanning in our patients who have ventriculomegaly or rapidly progressive macrocephaly or hydrocephalus, we can use it long-term without having to worry about that risk of radiation.
Dr. Michelle Machie:
And I would say the drawbacks for MRI, it's really the least available. Most centers will have a head ultrasound and CT scan. It's much harder to have an MRI machine available to babies at any center. We're really lucky at one of our centers in Dallas, at Parkland, to have an MRI scanner in the unit. And so, usually if MRI is available again, the baby's being transported off the floor. This is the most expensive modality, but I'll say we do have various imaging protocols we can implement to shorten the duration of the imaging and to even image without sedation, to kind of ameliorate some of those drawbacks.
Dr. Neeta Goli:
And what are specific indications for each of these modalities to be used?
Dr. Michelle Machie:
So I would say ... We'll start with head ultrasound again. So for head ultrasound, I would say that outside of the surveillance protocol for preterm infants at risk for intraventricular hemorrhage, we should really be using it quite liberally as an initial screening tool. And any infant who's presenting with evidence of neurological dysfunction. And widely, that might include things like we talked about earlier, macrocephaly, poor feeding, seizures, abnormal movements, signs or symptoms of infection, or any abnormalities in the neurological exam. So I would have a low threshold to screen with head ultrasound, if there's any concerns.
Dr. Michelle Machie:
And then, if the pretest probability for brain abnormalities is pretty low and the head ultrasound returns normal, then in that setting, that's the only test that might be indicated. If the head ultrasound returned abnormal, then typically we would recommend further evaluation with a more sensitive study, which is the MRI. And we do that often because the head ultrasound might be done for specific indications. Say, seizure-like activity. And then it comes back with no real problems, but with an incidental finding maybe of a chorus plexus cyst, or even agenesis of the corpus callosum. Which would be incidental and unrelated to the clinical question. But still would warrant further evaluation with an MRI to assess for any associated lesions or problems.
Dr. Michelle Machie:
And then for CT scan, I would really only use that in the nursery or NICU setting, if there was no access to head ultrasound or MRI, or if the infant was presenting with traumatic brain injury or concern for acute kind of brain stem dysfunction or herniation, something emergent. And really that is primarily to decrease the risk of radiation exposure.
Dr. Neeta Goli:
And then what would be the specific indications for MRI?
Dr. Michelle Machie:
And then specifically for MRI, I would say that we start really in our practice with babies who are not yet even born. So in our fetal consultation, that's kind of the first step, is we may see a mom who's had an abnormal 20 week ultrasound. And there are concerns for congenital brain anomalies. And typically those mommies will go on to have a fetal MRI. Once those babies are born, we always get, always, always get a postnatal MRI on the baby to confirm findings because things can change quite a bit. Especially with one of our most common consults, which is prenatal or congenital ventriculomegaly, can often look much better once the baby is born and can sometimes look worse. So we always want to confirm the extent of findings postnatally, and that's kind of the earliest consults that we'll get.
Dr. Michelle Machie:
Anytime you have an abnormal head ultrasound, I would say that we probably need to follow up with an MRI. And then in a baby who we've been following for specific neurological indications, such as hypoxic ischemic encephalopathy or seizures, an MRI is always indicated. And they're typically protocols, specific protocols, that we like to use.
Dr. Michelle Machie:
So in hypoxic ischemic encephalopathy, or HIE, we're looking for evidence of specific patterns of injury related to decreased oxygen and blood flow in the perinatal period. And so we prefer to get our MRI in that setting at around four to six days of life, to optimize our ability to visualize tissue abnormalities on the MRI. And on the specific sequences. If we get it too early, then we might miss some changes on the conventional imaging, or T1 or T2 sequences. If we wait too long, then a lot of the restricted diffusion changes, or DWI changes, can appear to have normalized.
Dr. Michelle Machie:
So there's a tight window for that. Every baby who has HIE or who has been managed for HIE or underwent therapeutic hypothermia should have an MRI in that window. And same thing, I believe, for any baby who's presenting with seizures that are confirmed should have an MRI prior to going home. Because there's typically going to be, if not a structural lesion, then we at least need to rule that out so that we can pursue metabolic and genetic evaluation. And then, as well as meningitis.
Dr. Michelle Machie:
Now, I will say in meningitis, I prefer to get an early MRI possible when the baby presents. And that's because of the same thing with HIE. We want to see those early restricted diffusion changes to see the full extent of the injury. Sometimes babies with meningitis or other critical illnesses are just too unstable to go to the scanner. And so there are definitely times with meningitis where we end up having to wait until the end of IV antibiotic or antiviral therapy to get the MRI.
Dr. Michelle Machie:
But the importance of the MRI in all of these settings, whether it be for congenital brain anomalies, HIE, seizures, meningitis. These are just a few indications that should always get an MRI, but the reason for the MRI is absolutely going to be for prognostication. And that's really what the parents want to know is, not just what does the imaging show, but what did that mean for my baby long-term? And that is the reason we do the MRI and do the most sensitive test, which is the MRI. And why we try to do it at specific timelines for each pathology so that we can provide the best prognosis for families.
Dr. Neeta Goli:
And then to switch gears for a second, from the brain to the spine, what physical exam findings or indications would necessitate imaging of the neonatal spine?
Dr. Michelle Machie:
Yes. And this is really a rare ... I would say neonatal spine abnormalities are a really rare consultation for us. But we do see them. And I would say the most common indication to image the neonatal spine is going to be probably .... You're probably concerned for occult spinal dysraphism. So either baby has an open spinal cord defect or has a tuft of hair or sacral dimple without base visualized, which would lead you to most typically, most commonly screened with an ultrasound.
Dr. Michelle Machie:
I will say, we try to recommend widely that if an infant has a sacral dimple and the base is visualized, or has the Y shaped gluteal cleft, which can be a normal variant, for those normal variants, we do not recommend imaging. We just follow the babies clinically. And usually those sacral dimples will resolve and go away as the baby grows.
Dr. Michelle Machie:
And then in the setting where you screen with the ultrasound, and there's a low, again, a low pretest probability, you may not need further evaluation. We typically follow those babies and make sure that they develop their walking on time. And in infants who have an abnormal ultrasound or who have a more extensive spinal defect, then definitely an MRI is the test of choice in that setting. An MRI of the spinal cord.
Dr. Michelle Machie:
I would say another common indication, or probably the second most common indication to image the neonatal spine would be for muscle tone or weakness. So hypertonia, increased muscle tone, could be a sign of an ongoing or congenital spinal cord lesion. It could also present with hypotonia, depending on what the insult is and the timing of the insult. For example, a perinatal spinal cord infarct, or stroke, might initially present with a baby who's low tone and weak. And then over time becomes hypertonic with increased tone and tight in the muscles. And hyperreflexia as the spinal cord and the muscles adapt to those changes from the injury.
Dr. Michelle Machie:
So in a baby who has increased muscle tone, I will often include spinal cord imaging. In a baby who has weakness, especially of the arm, and this is one case that I'll never forget. And why I keep this pearl about the Moro reflex is that I recently, in the last year, had an infant who was born full term and just not able to wean off respiratory settings. Initially thought maybe it was transient tachypnea or just transition problems. But just couldn't wean the respiratory settings and was having feeding difficulties.
Dr. Michelle Machie:
And the NICU team just thought the baby didn't look right, wasn't moving right. And on the physical exam, this baby had an absent Moro reflex and was not moving the arms fully in the air. Right? So baby should be able to lift both arms fully anti-gravity in response to your touch. Or at least in response to painful stimuli. And this baby wasn't doing that. And that made me worried about the cervical spinal cord. Okay? Because then we're talking about nerve innervation to the arms and then everything below. So that baby ended up having an extensive spinal cord tumor. But we really want to be watchful for any variations in muscle tone, weakness, or reflexes to help us decide if we need spinal cord imaging in the neonate.
Dr. Neeta Goli:
And that was a great anecdote and very, again, kind of sheds light on the importance of the physical exam and kind of putting it all together, too. Why is it that ultrasound is a preferred imaging modality for the spine?
Dr. Michelle Machie:
So ultrasound, we have a tight window in the neonate where we can easily access the bony structures and the fluid structures and see all of those quite well. And the technicians have a great way to use the windowing. But I would say that it is a tight window. So once the infants grow past a few months of age, the ultrasound is not going to be as good an exam. So it's something that we can do if the baby is in the NICU, newborn within those first month or two of life, we can use the ultrasound that's available to us. And it's preferred really because it's fairly inexpensive, rapid to do, and accessible.
Dr. Michelle Machie:
Whereas sending them straight for the MRI is a bit of a bigger test. And oftentimes, depending on where you are, the center may require the baby to be sedated, to undergo anesthesia. It's a longer study, it's more expensive. So when we can, if we catch the baby in that window where they're still quite little, that we can use an ultrasound of the spinal cord. And then once the baby is a little bit older, we'll have to switch, we'd have to switch to an MRI.
Dr. Neeta Goli:
In what clinical situations would you recommend we consult you in neurology before ordering neuroimaging?
Dr. Michelle Machie:
So we provide neurology consult, here at UT Southwestern and the affiliated NICUs. And at least for our group, if any neuroimaging specifically MRI, is going to be ordered, we really prefer to meet and discuss with the family ahead of time. Before the imaging is done. One, really, to allow them to get to know us, to develop trust, to build that relationship so that when results do come back, there's already a bond in place there between us and the family.
Dr. Michelle Machie:
And the NICU or nursery stay can be so emotionally traumatic to parents and to families. And the stress of receiving results, any results, especially ones that they might've been anticipating for weeks or for months. And for months, like the babies who are waiting for their term equivalent MRI, who were born premature, the stress of that timeline of waiting for results only adds to kind of all that emotional trauma.
Dr. Michelle Machie:
So in our group, we try our best to ameliorate the stress by creating positive, trusting relationships, not rushing the families, trying to meet them beforehand, and then sitting down with them through these results and really to help them to help ensure that they understand and have good comprehension of everything we're saying. So if it's going to be an MRI, we definitely prefer to be consulted before it’s done. Even when, if they're just thinking, I wonder if an MRI might be needed, that would be a great time to call. And we can have a discussion about what is the indicated neuroimaging modality, would MRI be the best fit, the timing for the MRI. And then decide together if neurology should come and do the full consult and meet the family. Which we love to do ahead of time.
Dr. Michelle Machie:
So that's specifically for MRI. I would say for head ultrasound, as it's used in the NICU and the nursery more as a quick kind of ASAP screening tool, for that specific modality ... It's reasonable to go ahead and do that one without consulting neurology first. And then if it returns abnormal, if the ultrasound returns abnormal, we're happy to consult and to discuss whether or not additional testing is needed.
Dr. Michelle Machie:
And then for CT scan, again, that's typically going to be something where you need to make the call quite emergently. So I would say in those settings, because of the timeline, it's typically reasonable to go ahead and get that done. Unless the question is ... The specific question is going to be, should we do a CT scan or MRI? Then either call us first or call radiology. It's always important to make sure, not only that you've ordered the right test, but that you've placed the right indication in the comments. That we're doing the right protocol. One MRI does not fit all. We have specific protocols that we do for epilepsy, a different one for HIE, a different one for meningitis sometimes.
Dr. Michelle Machie:
And so it's really important that we, if there's any question about how to place the order, what it should say, for any of the modalities, that you either called neurology. We're happy to talk that through. Or discuss with radiology. And then there's more resource-limited settings where in-house neurology is not readily available. In our practice, we definitely welcome phone consultations, and we can provide assistance in helping to determine the best neuroimaging modality and help answer any questions that might be at hand.
Dr. Neeta Goli:
Are there any new or emerging technologies or imaging modalities we should be aware of?
Dr. Michelle Machie:
So I would say to that, again, the field is growing rapidly, both of neonatal neurology and also of neuro imaging and its applications to the neonate. So we now have diagnostics such as MR spectroscopy, which we didn't have a few decades ago. MR spectroscopy is a tool that allows for the in vivo or cellular detection of various brain metabolites, such as lactate, which is important to look for in HIE.
Dr. Michelle Machie:
And so we routinely use that now in infants with HIE or hypoxic ischemic encephalopathy, to determine the extent of brain injury. And it's been shown to have great sensitivity, specificity, and predictive values for long-term neurodevelopmental outcomes. There's a lot of ongoing research on how MR spectroscopy and other MRI modalities can be used to provide long-term prognostication for neurodevelopmental outcomes.
Dr. Michelle Machie:
Another area where people are evaluating kind of these advanced MRI techniques is in diffusion tensor imaging, or DTI. This modality evaluates the white matter tracts. And so we can use it to see are any white matter tracts abnormally formed or missing. And then we're trying to learn more about how those might correlate to long-term speech or motor or cognitive disabilities.
Dr. Michelle Machie:
And then another one is called BOLD or blood oxygen level dependent imaging. And that's a way of functionally characterizing cerebral blood flow. And I think all of these are going to be really exciting frontiers for exploration in the neonatal brain. And then lastly, I am in no way affiliated with this other project that I'm going to talk about, but there is a new FDA-approved in-NICU scanner, MRI scanner, called Embrace. And it's been developed by Aspect Imaging. It's FDA approved, and it's an MRI scanner that is sized for infants, and it kind of lives inside the NICU to minimize those transport concerns that you might have with your off-the-floor MRI scan.
Dr. Michelle Machie:
And so this is really exciting, kind of new technology that's sweeping the field. And we don't have this in Dallas, at our Dallas campuses just yet. But I see this as being an option for typically, I would say for larger NICU, with larger volume, with infants who are already requiring an MRI frequently. And so eventually this may be something we get to work with here in Dallas, as well.
Dr. Neeta Goli:
So lots of exciting stuff coming down the pipeline. To end the episode today, do you have any advice for our listeners while they care for newborns?
Dr. Michelle Machie:
So I think to everybody out there who joins me in caring for newborns, I would say thank you for the work that you do. For me, the brain is the most important organ. And we really want to solidify Dallas and our centers as leaders in brain-focused neonatal care. So if you have any interest in advancing brain protocols or learning more about brain-centered care, then please feel free to reach out. I'm always happy to talk about this, to talk about neonatal neuroimaging. And we can always use more advocates in this rapidly growing field.
Dr. Michelle Machie:
And I would say, don't hesitate to call us - to call your neurology colleagues. If you have questions about what specific modality is the best, it's going to be the give you the best answer for your patient and their family, we're always happy to think that through with you. And we want to make sure that these babies are getting the best care and the best brain-centered care. And thank you so much for having me today.
Dr. Neeta Goli:
Thank you. Thanks again for joining us today, Dr. Machie. Thanks for listening to Newborn News. We hope you join us next time. If you like what you hear, make sure to subscribe and leave us a review. If you have questions, comments, feedback, or suggestions for future episodes, please email me at NewbornNews@utsouthwestern.edu. As a reminder, this content is educational and is not meant to be used as medical advice. Views or opinions expressed in this podcast are those of myself and my guests and do not necessarily reflect the views of the university.