According to Davies ⁴ the ‘anterior horn width’ is the width of the anterior horn of the lateral ventricles measured in the 3D coronal view at the level of the foramen of Munro. The width is measured on each side as the distance between the medial wall and floor of the lateral ventricle at the widest point. The linear measurements taken in their study of infants with a mean age of < 33 weeks’ gestational age at birth were

• anterior horn width

• thalamo-occipital distance of the lateral ventricles

• width of the third ventricle

• width and length of the fourth ventricle (Fig. 9.2 and reference values Table 9.1).

Figure 9.2 A line drawing showing the measurements made on the ultrasound images, with arrows indicating the correct caliper position and alignment (A, coronal plane; B, parasagittal plane; C & D, transverse plane). Reference values are given in Table 9.1.

Table 9.1 Reference values

The width of the ventricles may be expressed as a ratio of the total width of the cranium, the ventricles may be measured directly and now, with 3D techniques, volumetric measurements have all been reported. Using measurements expressed as a ratio does not reliably monitor growth and measurements of both ventricles and cortex may not even produce an abnormality when expressed as a ratio. Direct measurement of the ventricles is still the simplest, most reproducible and easy-to-teach technique.

The occipital poles enlarge before the body of the lateral ventricles, but measurements are unreliable and impractical due to the wide range of size and shape of the occipital horns. Measuring the biventricular diameter is also not reliable, as one ventricle may enlarge more rapidly than another (Box 9.1).

BOX 9.1 Tips for cranial ultrasound

• If monitoring equipment in situ, ensure it is well secured

• Get parent or helper to immobilize the head

• Use a high-frequency transducer that fits snugly onto the anterior fontanelle. Try supplementary views if needed

• Start in the coronal plane and look for symmetry of the right and left cerebral hemispheres and intracranial structures

• Check that the normal anatomic structures are distinguishable

• Does the cortical folding appear appropriate for age?

• Is there normal distinction between cortex and white matter?

• Is there appropriate echogenicity of the periventricular and subcortical white matter and the basal ganglia and thalami?

• Is there peri- or intraventricular hemorrhage?

• Asymmetric, echogenic (greater than the choroid plexus) areas are usually abnormal

• Occipital flare can be a normal finding

• Is there calcification?

• Evaluate the subarachnoid space and fissures: > 5 mm is usually abnormal

• Evaluate the size and width of the ventricles. Asymmetry in ventricular size can be normal

• Slit-like ventricles in the absence of other changes can be normal

Subarachnoid space

The subarachnoid spaces should be carefully evaluated and linear dimensions taken in the coronal plane at the level of the foramen of Monro (Fig. 9.3).⁵

• Craniocortical width (CCW) — widest vertical distance between calvarium

• Sinocortical width (SCW) — widest distance between lateral wall of superior sagittal sinus and surface of cortex

• Interhemispheric width (IHW) — widest horizontal distance between the hemispheres

Figure 9.3 Anatomic landmarks and sonographic variables of the subarachnoid space in the coronal plane. C = cerebral cortex; SSS = superior sagittal sinus; CCW = craniocortical width; IHW = interhemispheric width; SCW = sinocortical width.

The authors have produced reference tables for infants in their study (median age 8 weeks — age range 1 day to 1.5 years) showing there was an increasing trend in of all the widths up to 28 weeks, after which a decline was observed. Broadly speaking, in the term baby a measurements over 4–5 mm is abnormal.

Normal anatomy

Cranial ultrasound examinations are performed in the coronal and sagittal planes (Fig. 9.4A,B). Additional acoustic windows are found through the temporal bone and mastoid fontanelle (Fig. 9.4C).

Figure 9.4 Technique of cranial ultrasound—intracranial scanning: (A) the coronal planes and (B) the sagittal planes. (C) The additional acoustic windows that can sometimes be employed.

Coronal section

Coronal planes are:

• through the frontal lobes

• through the frontal horns of the lateral ventricles

• foramen of Munro and third ventricle

• lateral ventricles and choroid plexus

• occipital lobes.

Sagittal planes

Rotate the transducer 90° from the coronal section. Angle the beam approximately 20° from the midline, both right and left, to obtain the full length of the lateral ventricles:

• midline through the third ventricle aqueduct, fourth ventricle and cerebellum

• right lateral ventricle

• right parietal lobe

• left lateral ventricle

• left parietal lobe

• additional views if necessary.

Axial planes

Axial planes are not routinely used but can be extremely useful if subdural or extra-axial fluid is suspected. Axial sections can be difficult to understand, so are best taken at the body of the lateral ventricles where anatomy is easily recognized (Fig. 9.5).

Figure 9.5 Series showing normal anatomy MRI with ultrasound scans. (A) & (B) MRI scans at the level of the third ventricle to compare with the cranial ultrasound at the same level. The third ventricle (3) is a small slit-like structure in the midline below and between lateral ventricles. The connection with the lateral ventricles at the foramen of Munro (FoM) can be clearly seen and is an important landmark. The sylvian fissure (SF) is an important landmark laterally and becomes deeper the more posterior the scan. (C) Coronal scan at the level of the quadrigeminal cisterns just posterior to (B) showing the frontal horns of the lateral ventricles. There is a small cavum centrally and some echogenic choroid plexus in the floor of the lateral ventricles. (D) Moving the transducer posteriorly the lateral ventricles can be seen containing the echogenic choroid plexus (cp). Symmetry of the choroid can be assessed in this view. (E) Coronal section posteriorly over the sulci and gyri of the occipital lobes. The surface of the brain must be examined to assess for fluid collections and gyral pattern. (F) & (G) Midline sagittal MRI and ultrasound to compare the normal anatomy. This is a very useful image and can clearly demonstrate the echogenic cerebellar vermis (v), fourth ventricle (4) and third ventricle (3). The corpus callosum can be seen as a C-shaped structure just above the third ventricle. (H) Para-sagittal view of ventricle. This is a section through the lateral ventricle. The caudate nucleus (c) lies in the floor of the lateral ventricle and the caudothalamic groove is the landmark from which the choroid plexus (cp) inserts posteriorly. The caudate nucleus is more echogenic than the thalamus. The echogenic flare (flare) in the occipital white matter can be a normal finding.

The ventricular system

The ventricular system of the brain consists of two lateral ventricles, a third ventricle aqueduct of Sylvius and a fourth ventricle.

The lateral ventricles are the largest and consist of the frontal horn, the body, the temporal horn and the occipital horn. They all communicate and, in addition, they communicate with the subarachnoid spaces. They communicate with the third ventricle via the foramen of Munro and the fourth ventricle via the aqueduct of Sylvius. The third ventricle is not easy to see on the coronal scan as it is a slit-like structure, neither is the aqueduct on the sagittal scan. The fourth ventricle has the typical rhomboid ‘Napoleon’s hat shape’ and extends into the cerebellar vermis (Fig. 9.6).

Figure 9.6 Ventricular dilation. (A) Coronal scan in an infant who had had an intraventricular hemorrhage. There is dilation of the lateral ventricles with blood clot lying in the occipital horns. There is quite marked dilation of the third ventricle (short arrow) and the fourth ventricle (long arrow). (B) Midline sagittal scan on the same infant showing the dilated third ventricle (short arrow) with the massa intermedia and dilation of the fourth ventricle (long arrow). The cerebellum is compressed posteriorly and there are echogenic areas of blood clot within the dilated ventricles.

Coarctation of the lateral ventricles is a normal variant, where there are cystic areas adjacent to the superolateral angle of the lateral ventricle at the level of the foramen of Munro. These cysts appear as a string of beads along the floor of the lateral ventricle. In some of the literature this is called subependymal pseudocysts. It is important not to confuse these with periventricular leukomalacia (Fig. 9.7).⁶

Figure 9.7 Coarctation of the ventricles. (A) Coronal scan showing the anterior horns of the lateral ventricles. There are cystic areas lateral to this (arrows). This is not periventricular leukomalacia but rather a normal appearance called coarctation of the ventricles. (B) Sagittal scan through the right lateral ventricle. There are two cystic areas just beneath and lateral to the anterior horns of the lateral ventricles. Echogenic choroid is lying posteriorly within the ventricle.

Choroid plexus

The choroid plexus comprises the two paired echogenic structures which lie in the floors of the lateral ventricles. They are best seen in the sagittal scans extending anteriorly from the caudothalamic groove extending around the thalamus in the body of the lateral ventricle. When scanned coronally, they can be seen in the floor of the lateral ventricles in the region of the foramen of Munro. Choroid plexus cysts are often seen as incidental findings.

Cavum septum pellucidum and cavum vergi

The lateral ventricles are separated by the septum pellucidum. Occasionally, and in particular in preterm infants, a cavity is seen between the two leaves due to incomplete fusion. The cavum septum pellucidum lies anteriorly and the cavum vergi posteriorly. They are almost always seen in the preterm and obliterated by term. They vary in size and do not communicate with the ventricular system.

Corpus callosum

The corpus callosum is the C-shaped structure lying above the third ventricle. It should always be identified and normally measures 44 mm in length at term when measured in the sagittal plane from the anterior aspect of the genu to the posterior aspect of the splenium.

The basal ganglia

The basal ganglia is the area seen best at the level of the foramen of Munro and consists of the caudate nucleus and thalamus. They are separated by the caudothalamic groove, an important landmark when assessing for germinal matrix hemorrhages. The two thalami are connected via the massa intermedia, which can be seen in a pathologically dilated third ventricle (see Fig. 9.6).⁷

Cerebellum

The cerebellum is a rounded echogenic structure seen in the posterior fossa. It lies behind the pons in the fourth ventricle, and the vermis is a particularly echogenic central structure.

INTRACRANIAL HEMORRHAGE

The major cause of intracranial hemorrhage used to be trauma during delivery. Nowadays the major cause is prematurity, as the brain of the premature infant is highly susceptible to ischemia and hypoxia. Other causes include hypothermia, coagulopathy and pneumothoraces. One of the major roles of intracranial ultrasound is in the detection of hemorrhage, and the intracranial sites of hemorrhage are different depending on the etiology and age of the infant. The optimal time for scanning is 72 hours after birth. All periventricular hemorrhages occur after birth and within the first week of life, and the incidence of hemorrhage is directly related to prematurity.

All at-risk infants should have a scan by 7 days repeated at 14, as a small percentage will be missed on the first scan.

All infants under 34 weeks should be routinely scanned.

Bleeding may occur in a number of places related to the skull and intracranial contents. Fresh blood always appears highly echogenic. After a few weeks these intraparenchymal hemorrhagic areas may liquefy and become cystic.

The following should always be assessed:

• basal ganglia, particularly the area of the germinal matrix in the floor of the lateral ventricles

• ventricles for size and intraventricular hemorrhage

• cerebral parenchyma, particularly periventricular region for flares

• choroid plexus for symmetry

• cerebellum

• extra-axial fluid such as subdural and subarachnoid collections (Fig. 9.8).

Figure 9.8 How to differentiate subdural from subarachnoid hemorrhage. Line diagram showing the anatomy related to the subarachnoid and subdural spaces. This demonstrates the rich network of blood vessels in the subarachnoid space. If there is an increase in fluid in this space, using Doppler one can demonstrate small vessels crossing, whereas with subdural fluid these small vessels are compressed on the surface of the brain.

Types of intracranial hemorrhage

Germinal matrix

This is a small area of brain occurring in the floors of the lateral ventricles and best seen on anterior coronal scans. This area is very vascular in the premature infant and that is why these hemorrhages occur primarily in the premature infant. It has a rich matrix of fragile capillaries and it is alterations in cerebral blood flow that causes vasodilation of these tiny vessels leading to hemorrhage. This may be an isolated finding but they occasionally will rupture into the ventricle and in a small percentage will rupture into the parenchyma through the roof of the lateral ventricle. By term and increasing gestational age the subependymal plate has almost completely disappeared. There is almost universally a good prognosis, with only a very small number (2%) reportedly resulting in neurological sequelae.⁸

Small germinal matrix hemorrhages, if they are fresh, appear echogenic. They may occasionally be mistaken for choroid in the floor of the lateral ventricle. Hemorrhages need to be confirmed in the sagittal view and occur anterior to the caudothalamic groove. There is no distortion of the ventricular system and after a number of weeks they may become cystic and eventually disappear as the brain grows (Fig. 9.9).

Figure 9.9 Germinal matrix hemorrhage. (A) Coronal scan through the anterior horns of the lateral ventricle. There is an echogenic area in the region of the germinal matrix on the right (arrow). (B) Sagittal scan through the right lateral ventricle showing the echogenic area in the region of the thalamus (between calipers). This is a fresh germinal matrix hemorrhage. On the sagittal view a germinal matrix hemorrhage always occurs anterior to the caudothalamic groove. (C) Coronal scan anteriorly showing the anterior horns of the lateral ventricles. There is a large cavum centrally and cystic areas in the floors of the lateral ventricles on both the right and left side. This is the appearance of bilateral old germinal matrix hemorrhages with residual cystic change. (D) Sagittal scan through the lateral ventricle in a normal child showing the caudothalamic groove. This is an important landmark as no increase in echogenicity should be seen anterior to this groove in the basal ganglia.

Periventricular hemorrhage

Periventricular hemorrhage (PVH) is the commonest parenchymal hemorrhage to occur. It is a loose term and encompasses germinal matrix hemorrhages (subependymal hemorrhage—SEH) and intraventricular rupture with parenchymal extension.

Choroid plexus hemorrhage

Choroid plexus hemorrhage is not common and tends to be more a term event. Fresh hemorrhage and blood in the choroid plexus may be missed due to the similar echogenicity of the paired choroid plexus structures. In association there may be fluid blood in the ventricles, which can sometimes adhere to the choroid. Hemorrhage should be diagnosed when the choroid plexus appears enlarged, asymmetrical or irregular in outline. Associated occipital horn dilation is sometimes seen. Generally there is no subarachnoid blood seen. Choroid plexus diameters of 12 mm or more are suggestive of hemorrhage.

Intracerebellar hemorrhage

Cerebellar hemorrhage is well described and may occur in the preterm and term infant. Hemorrhage may occur due to a bleeding disorder or trauma, and has been associated with tight-fitting face masks.⁹ The cerebellum is normally echogenic but hemorrhage may increase the echogenicity. It may be unilateral with an irregular outline.

Ultrasound is not a reliable method of making this diagnosis, as blood around the tent may be confusing.

Thalamic hemorrhages

Primary thalamic hemorrhages are extremely rare.

Subdural hemorrhages

Subdural hemorrhages are caused by trauma at birth, non-accidental injury, and bleeding disorders. Bleeding results from dural tears.¹⁰^–¹²

Subarachnoid hemorrhages

Subarachnoid hemorrhages may be due to blood in the ventricular system due to an intraventricular hemorrhage or from a bleeding diathesis and bleeding from the vessels. Other causes include passive dilation of the subarachnoid space, which may be due to brain atrophy, subdural effusion or abscess which may develop as a result of meningitis and subdural hemorrhages at various stages. Visualization of the cortical veins and their branches within fluid collections around the brain suggest that the pericerebral collection is caused by an enlarged subarachnoid space and not a subdural. This is best demonstrated with color Doppler to show the flow in superficial cortical vessels which lie along the superficial gyri and sulci.

Differentiation of subdural and subarachnoid hemorrhages can be difficult on ultrasound (Fig. 9.10) (Table 9.2).

Figure 9.10 Extra-axial fluid. (A) Coronal scan posteriorly, showing the echogenic choroid plexus in the lateral ventricles. Notice the extra-axial fluid enhancing the gyri of the brain. (B) Magnified view anteriorly in the same infant. There is a combination of subarachnoid and subdural fluid. The line of the elevated dura can be identified. (C) CT scan of the same infant showing the large amount of fluid predominantly over the frontal lobes.

Table 9.2 Differentiation of subdural and subarachnoid hemorrhages

Subdural	Subarachnoid
If large may have midline shift Look for linear elevation of dura Does not follow convolution of gyri Compressed flattened gyri May be hyperechoic if fresh blood and hypoechoic if old May be localized to one area and not lying diffusely over cerebral cortex	Either hyper- or hypoechoic, depending on age of blood Doppler will show vessels crossing the subarachnoid space Usually follow the line of the gyri Look for blood in the sylvian fissure

Classification

There is no internationally accepted grading system for germinal matrix hemorrhage/intraventricular hemorrhage (GMH–IVH). Tables 9.3 and 9.4 outline the grading systems for periventricular hemorrhage used for ultrasound scanning.

Table 9.3 Grading system for PVH used or adapted for use with ultrasound brain scanning ⁹

Grade I	Isolated SEH
Grade II	Rupture into ventricle, but no dilation
Grade III	Rupture into ventricle with dilation
Grade IV	IVH with parenchymal extension

IVH, intraventricular hemorrhage; SEH, subependymal hemorrhage.

Table 9.4 A modification of the grading system suggested by Levene and de Crespigny ¹⁴

HEMORRHAGE
0	No hemorrhage
1	Localized hemorrhage <1 cm in its largest measurement
2	Hemorrhage >1 cm in its largest measurement but not extending beyond the atrium of the lateral ventricle
3	Blood clot forming a cast of the lateral ventricle and extending beyond the atrium
4	Intraparenchymal hemorrhage
VENTRICULAR DILATION
0	No dilation
1	Transient dilation
2	Persistent but stable dilation
3	Progressive ventricular dilation requiring treatment
4	Persistent asymmetrical ventricular dilation

The advantage of Papille’s grading system is that it is simple and easy to understand.⁹ Levene’s grading system has also gained some acceptance but it is more complicated and neither take account of periventricular leukomalacia.¹³

It is far better to document the site and size of the hemorrhage and, if there is ventricular dilation, to measure it (Fig. 9.11).