Dr Ahmed Sherif, Royal Cornwall Hospital
Why should a paediatrician learn cranial ultrasound? We can always ask a radiographer or a radiologist to do it, right?
Well, that’s fine if you can guarantee that you will have a radiologist overnight when you are concerned about a potential IVH… or when you want to be sure there is no midline shift calling for an urgent neurosurgical review.
Cranial ultrasound (CRUS) is a tool and a skill that can be extremely useful and beneficial in paediatrics, especially in NICU.
- Early imaging
- Serial imaging which can help to assess evolution of lesions
- No need for sedation
The main disadvantage is that it is subjective and depends on the operator.
CrUS uses Transducers with frequencies ranging from 5–7.5–10 MHz that are appropriately sized for the neonate
- Standard examination: use 7.5–8 MHz
- Tiny baby and/or superficial structures: use higher frequencies
- Large baby, thick hair, and/or deep structures: use lower frequencies
The acoustic windows:
Bone is not permeable to ultrasound waves. An acoustic window is the location from which ultrasound waves permeate the deep structures. That is why cranial ultrasound is only feasible in newborns and infants because they still have open fontanelles. The fontanelles and other non-bony structures shown in figure (1) are the acoustic windows used to scan the brain.
As paediatricians, we are usually interested in the standard window, the anterior fontanelle.
So, let’s start the scan on a normal baby. I’ll talk you through it.
Anterior fontanelle coronal view:
In this view you should hold the probe at the anterior fontanelle with the transducer’s marker pointing to the right of the patient (check your local machine’s set-up):
You need to get 6 standard images on your coronal scan. The coronal view is your best tool to scan the whole brain looking for abnormalities.
It is called coronal as the line your ultrasound probe is using to draw the plane is the same line a tiara or a crown would lie on if put on the baby’s head; corona means crown (figure 2a).
The 6 standard images should be aimed at the planes shown in figure (2b).
So, to start, make sure the baby is as calm as possible. Then, point the probe to the right side of the baby and tilt the probe aiming to the front while keeping it at the anterior fontanelle. You can use this image to make sure you are getting symmetrical images with your scan. Here (Figure 3) you should be able to see the frontal lobes of both cerebral hemispheres (2) separated by the Falx cerebri (1). They will be lying on top of bright hyperechoic transverse lines; these are the supra-orbital ridges (3).
Next, start tilting the probe slowly back by lifting the tail of the probe up (tilting the top of the probe towards the eyes). You should have your second image at the first sight of the anterior horns of the lateral ventricles (5). Just below each lateral ventricle is the caudate nucleus and the basal ganglia ((6) & (7) respectively). You can appreciate the Y-shaped sylvian fissures (9) on both sides (Figure 4).
Keep going back (raising the tail of the probe) and as soon as you have an image like figure (5), stop. This is the most informative cut in the coronal view. So, you already know that (5) stands for the anterior horn of lateral ventricle. I want you to focus on the midline. So, from the top downwards, you have the falx cerebri (1), cingulate sulcus (13), Corpus callosum (10) and note the two parallel white lines, cavum pellucidum (11) which is a normal finding in 15% of the population and in most premature babies. Last but not the least: The third ventricle (12). Try to remember that it should be “slit-like” as a norm. This is the best image to evaluate ventricular dilatation and to measure the ventricular index to assess hydrocephalic changes.
OK, you are half done with this view.
Keep going backwards till you notice bilateral hyperechoic signals lying on the lateral ventricles (14). These are the choroid plexuses (15). You need to observe the echogenicity (brightness) of the choroid plexuses against any other hyperechoic findings (things that look bright on ultrasound scans), that will be useful in the diagnosis of periventricular leukomalacia (PVL) for example.
Another interesting thing you can observe on this image is the sub-tentorial structures like the brain stem (19) (the tentorium is a fold of the dura mater forming a partition between the cerebrum and cerebellum).
Your fifth image (figure 7) within the coronal view will be at the level of the occipital horns of the lateral ventricles. The lateral ventricles (21) here look different as you are cutting them where they are making a U-turn downward and forward again.
You can see the choroid plexuses (15) again lying on the floor of the lateral ventricles looking like two rods.This time, you can appreciate the cerebellum and the cerebellar tonsils being visible on the lower part of the image (22b) and (22a) respectively
Now, the last image to finish the coronal view part of your scan is where you make sure the occipital lobes don’t have anything abnormal happening (Figure 8). Just as what we were doing with the first image, just be sure there is no mass, no haemorrhage and no abnormal structures or midline shifting.
Good job! Now, rotate the probe 90 degrees so, that the marker faces the forehead of the baby to start the sagittal view scan (the sagittal plane is where you cut the head to right and left halves) as in figure (9).
Anterior fontanelle sagittal view:
A lot of information? Don’t worry, fortunately, we only need to discuss three images with this one.
In my experience, finding the midline is the best way to start the sagittal view scan.
You need to know what to look for to allocate the midline image (Figure 10). The best finding is the third ventricle that is a rhomboid shape hypoechoic structure from this angle (12). You can see the corpus callosum above the septum pallucidum (10) and (11) respectively. Going down below the third ventricle, you will find the brainstem, (28) and (29).
Next, tilt the probe either to the right or the left slowly. The second image (Figure 11) should be taken when you find the lateral ventricle (14) visible all around from the anterior horn to the trigone to the occipital horn. This view is important to pick up the small bleeds in the germinal matrix which is found just inferior to the body of the lateral ventricle (14). You can appreciate the hyperechoic flare above the trigone (21) which is a normal flare. This is the watershed area of the parietal lobe that is most liable to get PVL as a complication of ischaemic events.
Last image to discuss to finish your scan is when you tilt the probe further to get to the parieto-temporal lobes (Figure 12). You only need to be sure you are not missing any haemorrhage, cysts or flares with this image on either side.
Remember to repeat images 2 & 3 on the opposite side, and then amazing, you’re done.
Well, this is as basic and simple as I managed to keep it. Try to practice getting the images under the supervision of a senior colleague who has experience with the cranial ultrasonography.
Index of Structures (numbered as per images)
|1. Interhemispheric fissure||23. Tentorium|
|2. Frontal lobe||24. Mesencephalon|
|3. Skull||25. Occipital lobe|
|4. Orbit||26. Parieto-occipital fissure|
|5. Frontal horn of lateral ventricle||27. Calcarine fissure|
|6. Caudate nucleus||28. Pons|
|7. Basal ganglia||29. Medulla oblongata|
|8. Temporal lobe||30. Fourth ventricle|
|9. Sylvian fissure||31. Cisterna magna|
|10. Corpus callosum||32. Cisterna quadrigemina|
|11. Cavum septum pellucidum||33. Interpeduncular fossa|
|12. Third ventricle||34. Fornix|
|13. Cingulate sulcus||35. Internal capsule|
|14. Body of lateral ventricle||36. Occipital horn of lateralventricle|
|15. Choroid plexus|
|(*: plexus in third ventricle)||37. Insula|
|16. Thalamus||38. Falx|
|17. Hippocampal fissure||39. Straight sinus (sinus rectus)|
|18. Aqueduct of Sylvius||40. Temporal horn of lateralventricle|
|19. Brain stem|
|20. Parietal lobe||41. Circle of Willis|
|21. Trigone of lateral ventricle||42. Prepontine cisternTentorium|
|22.Cerebellum (a. hemispheres b. vermis)|
In summary, CrUS is a very useful tool to quickly identify potential problems with neonates and infants such as haemorrhages, structural abnormalities, ischaemic sequelae and more. It is safe and easily performed bedside. It needs practice and familiarity with the standard views and images.
Best of luck,
Dr. Chris Warren, Paediatric consultant with neonatal Special interest, Royal Cornwall Hospital Trust
Dr. Simon Thorogood, Consultant radiologist, Royal Cornwall Hospital Trust
References for images and figures:
Meijler G. (2012) Neonatal Cranial Ultrasonography. Springer, Berlin, Heidelberg. ISBN 978-3-642-21319-9 e-ISBN 978-3-642-21320-5 DOI 10.1007/978-3-642-21320-5
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