Sonography of the Infant Brain - Anatomy - SD

Introduction

Good afternoon.

I'm Henrietta TLAs Rosenberg, director of Pediatric Radiology at the Mount Sinai Medical Center in New York City.

I'm also professor of radiology at the Mount Sinai School of Medicine.

I'm very pleased to speak with you this afternoon about sonography of the infant brain.

We'll talk about anatomy, hemorrhage, and hypoxic ischemic disease.

Learning Objectives

The learning objectives for this talk include learning the performance of brain ultrasound in infants to learn the normal ultra sonographic brain anatomy and to learn the ultrasound appearance of brain hemorrhage and ischemia, and they're sequelae in premature and full term infants.

Transducer Frequencies and Probes

We use a variety of transducer frequencies in the infants in those babies who are quite large, those who are more than approximately five to six months of age and who are full term.

We will generally use a three megahertz probe.

We will at times have to use a Kline broad bandwidth so that we can penetrate to the depths of the brain.

Normally the fontanel, the anterior fontanel is opened until about nine to 18 months of age.

This could be open longer in babies who are premature or babies who have increased intracranial pressure.

In babies who are somewhat smaller, we may use a five megahertz, and then in the babies who are premature or full term, we will in the neonatal period use an eight five megahertz.

For scalp lesions, we will generally use a linear array probe that is at least 10 megahertz, often going as high as 17 five.

The posterior fontanel is generally opened until zero to four months of age and may be open longer in premature infants and infants who have increased intracranial pressure.

Imaging Planes

Now we generally obtain our images using coronal and sagittal planes.

Coronal Plane

In the coronal plane, we're going to sweep the brain from anterior to posterior and we will be looking for certain landmarks.

This is a drawing showing a coronal section of the brain.

In an infant, we can see the interhemispheric fissure.

We see the cingulate gyrus.

This hammock shaped area below the interhemispheric fissure represents the corpus callosum, and then below the corpus callosum, we have the right and left lateral ventricles which connect via the foramina of Monroe bilaterally to the third ventricle.

We also notice the sylvan fissure in the region of the Sylvan fissure.

We will visualize the pulsations of the middle cerebral artery just above the corpus callosum, we will see the peric collosal artery, and within the cingulate gyrus, we'll see the pulsations of the collosal marginal artery.

The goal of the sonogram is to image as much of the brain as we need to to have a complete evaluation, which implies that we will at times be oblique the transducer to the right and to the left to see over the convexes of the brain.

Sagittal Plane

The object of the sagittal plane is to examine the midline structures for anomalies and to evaluate in a para sagittal plane, the ventricular system, as well as the parenchyma of the brain As we scan in a straight, anterior, posterior, or AP plane.

In the midline, we will see the corpus callosum, the genu, the body, the splenium, and just below the corpus callosum will have the cavem septum lucidum.

Below that area we have the third ventricle.

We will see the mass intermedia when that ventricle is enlarged.

And then this continues through the aqueduct of sylvius to the fourth ventricle will visualize the cerebellum and the ci sternum magna, as well as the brainstem.

And depending upon the gestational age of the infant, we may or may not see the convolutional markings of the brain.

As we look at the para sagittal views, we'll image the ventricular system, and as we extend our view more peripherally, we'll see the substance of the brain parenchyma.

Bear in mind that when you're trying to visualize the ventricles, that the frontal horn is more medially positioned than the occipital horns, and so the anterior portion of the transducer needs to be more medially positioned than the posterior portion of the transducer.

Ultrasound Anatomy

Let's look at some of the ultrasound anatomy.

This is a very far anterior view.

This view is very far anterior because you can see the left and the right orbits.

The interhemispheric fissure is seen here and note that there are little areas of brighter echogenicity in the frontal lobes.

This is what is referred to as the periventricular blush.

It represents vascular markings as well as neurons as they extend from the deep white matter to the cortex of the brain.

As we extend our view a little bit more posteriorly, but still in the anterior plane, we see that there is interhemispheric fissure.

Here's the cingulate gyrus.

We can see the corpus callosum here as a hammock shaped structure that is very poorly a coic that is just below the brain parenchyma.

Here in the frontal lobes, we have a portion of the right lateral ventricle, a portion of the left lateral ventricle, and we're beginning to get into the areas of the cau nuclei bilaterally represented by these slightly brighter areas of increased echogenicity.

We're also beginning to see these y shaped structures that represent the sylvan fissures.

As we come back just a little bit more posteriorly to an anterior mid coronal view, we again see the interhemispheric fissure.

With the cingulate gyri, we can see the corpus callosum and image, the lateral ventricles.

Note that the inferior lateral aspect of the frontal horns are concave and that we can see the choroid plexus as it goes through the foramina of Monroe as brighter areas of echogenicity and choroid plexus in the region of the roof of the third ventricle.

The third ventricle may or may not be seen on the anterior mid coronal views.

Note the syl fissures bilaterally and also the bright echogenicity that is in the region of the hippocampal gyrus bilaterally.

As we look at the region of the temporal lobes, the little dots that we see centrally in the temporal lobe represent the temporal horns.

A little bit more posteriorly.

We get to the mid posterior coronal view.

Note in this view that we see this pie shaped area of bright echogenicity that represents the cerebellum.

A little bit farther back, we've reached the posterior coronal view and we see these bright areas of increased echogenicity that are the gloma of the choroid plexus, which we'll look at in more detail.

When we look at the para sagittal views, these are generally quite symmetric.

As we look a little bit more posteriorly, we see the periventricular blush around the posterior portions of the brain, and we're looking here at the occipital lobes.

The periventricular blush represents vascular markings as well as neurons that are coursing from the deep white matter to the cortex of the brain.

One one may encounter a variant where there is asymetry in the size of the choroid plexus that is basically physiologic and not indicative of an abnormality.

Note that the right side of the baby's head is up on this particular view.

Remember that the choroid plexus is buoyed up by only one part of the roof plate, so that if there is a change in the position of the baby's head, the side that's up tends to appear larger than the side that is down.

Notice when we turn the baby's head the other way with the left side up, we now see that this gloss of the choroid plexus looks as though it is larger.

It really isn't. This isn't artifact of positioning.

If there's ever a question, you can always turn the baby's head, of course, with the support of the nurses because most of these babies are attached to life support systems, and it is extremely important not to dislodge an endotracheal tube or other intravascular catheters or enteric tubes.

Extra-Axial Fluid Spaces and Measurements

Also, consider the extra axial fluid spaces.

We measure routinely the sano cortical width by identifying the superior sagittal sinus measuring from the sinus to the outer margin of the cortex of the brain.

In a normal baby, we'll see that the Sano cortical width measures 0.4 to 3.3 millimeters.

We also routinely measure the cranial cortical width.

This is the depth from the cranium to the cortex, and this should not measure more than 0.3 to 6.3 millimeters.

We measure the interhemispheric fissure, and this should not measure more than 8.2 millimeters.

Here's the ultrasound rendition.

We're measuring from the superior sagittal sinus to the cortex of the brain bilaterally, and we're measuring from the cranium to the cortex of the brain as well as the interhemispheric fissure, and all of these numbers fit into a normal range.

Gyri and Convolutional Markings

Also, consider the presence, the number, and the configuration of the gyri, which are proportional to the gestational age of the infant.

Notice that it is not until 26 weeks gestation that we begin to see the development of the cingulate, sulcus and gyrus as the baby's mature from 26 weeks gestation up to full term, there is an increase in the number of convolutional markings until at term there are multiples.

This is an important detail to be aware of as there are certain congenital anomalies of the brain that are associated with lack of formation of the convolutions.

Corpus Callosum

The corpus callosum should be looked for on every brain ultrasound study.

This is the largest medial interhemispheric commissure that contains fibers that interconnect the cerebral hemispheres, thus allowing for sharing of memory and learning between the two sides of the brain.

The corpus callosum forms during the third to fourth fetal month.

It grows as a bud from the lamina.

Terminis grows upward and backward while the brain grows laterally.

And posteriorly notice too that there is a fluid space below the corpus callosum.

This is the cavem septum lucidum and the more immature the baby is, the younger the gestational age, there will be a posterior extension to this fluid-filled space called the cave virga.

This should not be mistaken for a cyst within the brain.

So here we have the genu, the body, the splenium of the corpus callosum, and here we see the ultrasound image of this anatomy.

This is the genu of the corpus callosum, the body, the splenium with the baby's head facing to our left and the posterior aspect of the baby's head.

To our right, this is a cingulate gyrus, and here we can see that there is bright echogenicity right below the cavem septum lucidum and the posterior extension, the cavem virga.

This represents the choroid plexus in the roof of the third ventricle.

This is third ventricle, and you might question, why does this third ventricle not look quite as koic as the fluid that's in the cavem septum lucidum and the cavem virga.

The third and fourth ventricles are extremely slender.

They measure no more than approximately one to two millimeters in width, and therefore it is somewhat difficult to get an image that does not pick up specular reflectors from the brain tissue on both sides of these midline ventricles.

So here we have the third ventricle with the region of the aqueduct.

Sylvia going down into the area of the fourth ventricle, we have the cerebellum.

This very brightly a coic structure due to the fact that it's quite vascular and there are multiple convolutional markings.

Below the cerebellum is the ci sternum magna, and this should be looked for on every midline ultrasound view.

And here we have some increased echogenicity in the region of the brainstem.

Notice that the brain itself, in terms of the parenchyma is a relatively hypoechoic structure.

So here's the genu, the body and the splenium of the corpus callosum third and fourth ventricles.

This is a baby who's somewhat more mature.

You can see that there are more convolutional markings.

They're a little bit serpiginous, which happens as they develop.

And here we have the genu, the body, and the splenium of the corpus callosum with a remnant of the cavem septum lucidum.

This line that you see centrally represents a septal vein.

Again, choroid plexus in the roof of the third ventricle, the aqueduct, the fourth ventricle, the brainstem cerebellum, and cisterna Magna notice that once the babies become full term, there is less visualization of the ca from septum lucidum.

Sometimes it is totally obliterated by that age.

And here we see the genu, the body, the splenium of the corpus callosum, the choroid plexus in the roof of the third ventricle.

Here's the fourth, the brainstem, the cerebellum, and the cisterna.

Magna para sagittal views allow us to visualize the lateral ventricles, and we see here the bony structures of the cranial vault.

This is the anterior, the middle, and the posterior cranial fosse.

We have more convolutional markings seen on this particular image, and we can see the various parts of the lateral ventricle.

This is the frontal horn, the body, the atrium of the lateral ventricle where the body, the occipital horn, and the temporal horns meet housed within the atrium of the lateral ventricle is the gloss of the choroid plexus.

This should be very smooth and it should taper toward the coth thalamic groove as well as toward the temporal horn.

We should not see choroid extending into the occipital horn of the lateral ventricle.

Note that there is an area anterior to the coth thalamic groove that is called the germinal matrix, and we'll talk about this in more detail in a minute.

We also have the region of the ate nucleus and the area of the thalamus.

You'll notice there are little fine lines that radiate back from the posterior aspect of the body of the lateral ventricle as well as the occipital horn.

This is the periventricular blush that I alluded to when we talked about the coronal plane imaging, and these represent the vascular markings as well as the nerve fibers that extend from the deep white matter to the periphery of the brain.

The initial description was that these lines were reminiscent of the strokes of an artist's brush.

Extremely important to see this detail and to be sure that it is less koic than the gloss of the choroid plexus.

If this area becomes brighter than the choroid plexus.

We need to be concerned about hemorrhagic and necrotic changes, and we'll talk about that when we discuss ischemic disease of the premature brain.

Going back a little bit more towards the lateral aspect, we can see the Sylvie and Fi, and if we would turn on Doppler, we would see the pulsations of the middle cerebral artery.

And coming out a little bit farther laterally, we see the area of the insula.

We also get another view that's known as the occipital mastoid view, where we use the probe right behind the ear along the region of a little opening in the skull known as the mastoid fontanel.

It's really only possible to see through this area in very young babies, and this allows us to see the lobes of the cerebellum.

Notice here, the right lobe, the left lobe, and we can see the area of the CI sternum magna.

A little bit easier to see when we put it into a view, which is in a more vertical presentation.