Methods of neurosonography

Standard neurosonography is performed through the large (anterior) fontanelle, on which an ultrasound sensor is placed to obtain images in the frontal (coronal), sagittal and parasagittal planes. When the sensor is positioned strictly along the coronal suture, sections are obtained in the frontal plane, then, by turning the sensor by 90°, sections are obtained in the sagittal and parasagittal planes. By changing the tilt of the sensor forward - backward, right - left, a series of sections are sequentially obtained to assess the structures of the right and left hemispheres. The axial plane (examination through the temporal bone) is used in rare cases when a more detailed assessment of additional pathological formations is necessary, in particular tumors, it is often used as an option for transcranial scanning in children after the fontanelle is closed (after 9-12 months). Additional fontanelles (posterior, lateral) are used in isolated cases, since in a healthy full-term child they are normally already closed. Evaluation of posterior fossa structures through the foramen magnum may be difficult due to the severity of the newborn's condition.

Neurosonography provides a qualitative assessment of the state of cerebrospinal fluid-containing structures (ventricular system of the brain, cisterns, subarachnoid space, cavity of the septum pellucidum and Verga's cavity); periventricular structures; large cerebral vessels and choroid plexuses; optic thalamus and basal nuclei; brainstem structures and formations of the posterior cranial fossa (cerebellum), and skull bones.

To obtain their images, a series of ultrasound sections in the frontal and sagittal-parasagittal planes are used.

1. F-1. Section through the frontal lobes. In it, bone formations are represented by bright hyperechoic structures of the frontal, ethmoid and orbital bones. The interhemispheric fissure and the falx sac are clearly visible as a hyperechoic, median structure dividing the brain into the right and left hemispheres. Lateral to the fissure, on both sides, areas of moderately increased echogenicity are determined - the semi-oval centers.
2. F-2. Section through the anterior horns of the lateral ventricles. On both sides of the interhemispheric fissure, thin anechoic structures of the anterior horns of the lateral ventricles are revealed, separated by a transparent septum. The falx cerebri is located medially above the corpus callosum, which is visualized as a hypoechoic horizontal line, delimited by the roof of the lateral ventricles and the transparent septum. Pulsation of the anterior cerebral arteries is noted above the corpus callosum. The caudate nuclei have slightly increased echogenicity and are localized symmetrically under the lower walls of the lateral ventricles. Hyperechoic bone structures are represented by the parietal bones and the wings of the sphenoid bone.
3. F-3. Section at the level of the interventricular openings (openings of Monroe) and the third ventricle. In this section, the anterior horns of the lateral ventricles are detected as symmetrically located narrow anechoic structures. When the sensor is moved forward and backward, linear anechoic interventricular openings are visualized connecting the lateral and third ventricles, the latter is defined as a thin, vertically located, anechoic strip between the thalamuses. To the left and right, under the lower wall of the anterior horns of the lateral ventricles, an echocomplex of the caudate nucleus (nucleus caudatus) is detected, below - the tegmentum (putamen) and the pale globe (globus palidum). The lateral grooves are visualized as symmetrically located lateral Y-shaped structures, in which pulsation of the middle cerebral arteries is visible during real-time examination. Above the corpus callosum, perpendicular to the interhemispheric fissure, echo-positive linear structures of the cingulate groove are determined. In the parenchyma of the right and left hemispheres of the brain, hyperechoic curved convolutions of the hippocampus are clearly visible. Between them, the vessels of the arterial circle of the cerebrum (the circle of Willis) pulsate. Bone structures are represented by hyperechoic parietal and temporal bones.
4. F-4. Section through the bodies of the lateral ventricles. In this section, the anechoic bodies of the lateral ventricles located on both sides of the interhemispheric fissure are visualized. The corpus callosum is represented by a hypoechoic structure along the midline, above which the pulsation of the anterior cerebral arteries is determined. Hyperechoic vascular plexuses are located at the bottom of the lateral ventricles, the brainstem and the fourth ventricle are visualized vertically. Between the convolutions of the hippocampus and the tentorium cerebelli are the inferior (temporal) horns of the lateral ventricles, the lumen of which is normally not visible. The caudate and basal nuclei (tegmentum, globus pallidus) are determined next to the optic tubercles. The lateral sulci are visualized as symmetrical Y-shaped structures in the middle cranial fossa. In the posterior cranial fossa, the tentorium and vermis of the cerebellum are revealed to be of increased echogenicity, the cerebellar hemispheres are less echogenic; the large cistern of the brain located under the cerebellum is anechoic.
5. F-5. Section through the triangle of the lateral ventricles. On the echogram, the cavity of the lateral ventricles is partially or completely filled with hyperechoic, symmetrical vascular (choroid) plexuses, which are normally homogeneous and have a clear, even contour. A small anechoic strip of cerebrospinal fluid is visible around the vascular plexuses in the lateral ventricles. The permissible asymmetry of the plexuses is 3-5 mm. The interhemispheric fissure is located medially in the form of a hyperechoic linear structure. The vermis and tentorium cerebelli are determined in the posterior cranial fossa.
6. F-6. Section through the occipital lobes. The hyperechoic parietal and occipital bones are clearly visualized. The median thin linear structure represents the interhemispheric fissure and the falx corporis of the dura mater. The pattern of convolutions and grooves is visible in the parenchyma of the occipital lobes of the brain.

To obtain a midsagittal section (C-1), the sensor must be positioned strictly in the sagittal plane. Sections in the parasagittal plane (C 2-4) are obtained by successively tilting by 10-15° (section through the caudo-thalamic notch), 15-20° (section through the lateral ventricle), and 20-30° (section through the "islet") from the sagittal scanning plane in the right and left hemispheres of the brain.

1. C-1. Median sagittal section. Hyperechoic bone structures are represented by the ethmoid and sphenoid bones, the posterior cranial fossa is limited by the occipital bone. The corpus callosum is visualized as an arcuate structure of reduced echogenicity and consists of the genu, trunk and splenium. In its upper edge, along the groove of the corpus callosum, pulsation of the branch of the anterior cerebral artery - the pericallous artery - is determined. Above the corpus callosum is the cingulate gyrus, below it are the anechoic cavities of the septum pellucidum and Verge, which can be separated by a thin hyperechoic strip. In most cases, these anatomical structures are clearly visible in premature infants. The III ventricle is anechoic, triangular in shape, with its apex facing the pituitary fossa. Its shape is due to the presence of the infundibular and supraoptic processes. The main cisterns of the brain are visible: interpeduncular, quadrigeminal, cerebromedullary. The posterior wall of the hypothalamic recess borders the interpeduncular cistern. The high echogenicity of this cistern is due to the many branches of the basilar artery and septa of the choroid. Behind the interpeduncular cistern are the cerebral peduncles of low echogenicity, in the thickness of which is the aqueduct, the latter is normally almost invisible. Below and in front is the area of the pons, represented by a zone of increased echogenicity. The anechoic, triangular-shaped IV ventricle is located under the pons, its apex protrudes into the hyperechoic cerebellar vermis. Between the lower surface of the cerebellar vermis, the posterior surface of the medulla oblongata and the inner surface of the occipital bone is the anechoic large cistern (cisterna magna). In the brain parenchyma, the cingulate, calcarine, and occipitotemporal grooves of high echogenicity are visualized. The pulsation of the anterior, middle, posterior, and basilar arteries is clearly visible.
2. C-2. Section through the caudothalamic notch. The echogram shows the caudothalamic notch separating the head of the caudate nucleus from the thalamus.
3. C-3. Section through the lateral ventricle of the brain. During the examination, the anechoic sections of the lateral ventricle are visualized: the anterior, posterior, inferior horns, body and triangle surrounding the thalamus and basal ganglia. In the cavity of the lateral ventricle, there is a homogeneous, hyperechoic vascular plexus with a smooth, oval contour. In the anterior horn, the vascular plexus is absent. In the posterior horn, its thickening ("glomus") is often noted. Around the ventricle, in the periventricular region, a moderate increase in echogenicity is noted on both sides.
4. C-4. Section through the "islet". The section passes through the anatomical region of the "islet", in the parenchyma of which hyperechoic structures of the lateral and small grooves are visible.

A feature of the brain of premature infants is the visualization of the cavity of the septum pellucidum and the cavity of Verge. Also, in newborns born at 26-28 weeks of gestation, a wide subarachnoid space is visualized. In premature infants - 26-30 weeks of gestation - the lateral (Sylvian) groove is represented by a complex of increased echogenicity, resembling the shape of a triangle or a "flag" due to insufficiently formed brain structures dividing the frontal and temporal lobes. In premature infants up to 34-36 weeks of gestation, symmetrical zones of increased echogenicity (periventricular halo) are determined in the periventricular region, which is associated with the peculiarities of the blood supply to this zone. Due to the different rates of maturation of the brain and ventricular system, the relative sizes of the lateral ventricles in a premature baby, as in a fetus, are significantly larger than in a mature full-term newborn.

In children after the first month of life, the echographic characteristics of normal anatomical structures of the brain depend, first of all, on the gestational age at birth. In children over 3-6 months, a "split" interhemispheric fissure is often visible in the coronal plane. The size of the large cistern after 1 month of life should not exceed 3-5 mm. If the size of the cistern from birth remains more than 5 mm or increases, it is necessary to conduct an MRI to exclude pathology of the posterior cranial fossa and, first of all, cerebellar hypoplasia.

When measuring the cerebral ventricles (ventriculometry), the most stable sizes are the anterior horn (depth 1-2 mm) and the body (depth no more than 4 mm) of the lateral ventricle. The anterior horns are measured in the coronary plane in sections through the anterior horns, interventricular openings, the body is measured in a section through the bodies of the lateral ventricles. The third ventricle is measured in the coronary plane in a section through the interventricular opening and is 2-4 (2.0 ± 0.45) mm. Evaluation of the size of the fourth ventricle is difficult; attention is paid to its shape, structure and echogenicity, which can change significantly in case of developmental anomalies of the brain.

Scanning technique

Use 7.5 MHz sensor if available: if available, 5 MHz sensor can be used.

Sagittal slice: Position the transducer centrally over the anterior fontanelle with the scanning plane in the long axis of the head. Tilt the transducer to the right to visualize the right ventricle, then to the left to visualize the left ventricle.

Frontal cut: Rotate the probe 90° so that the scanning plane is transverse, tilt the probe forward and backward.

Axial slice: Place the transducer directly above the ear and tilt the scanning plane upward toward the cranial vault and downward toward the base of the skull. Repeat the examination on the other side.

Normal midline anatomy

In 80% of newborns, the fluid-containing structure of the cavity of the septum pellucidum creates a median structure. Below the cavity, the triangular fluid-containing cavity of the third ventricle will be determined, and the surrounding structures will be normal brain tissue of varying echogenicity.

Sagittal section

Oblique sections on each side of the brain should be used to visualize the lateral ventricles in an inverted "U" shape. It is important to visualize the structure of the thalamus and caudate nucleus below the ventricles, as this is the area of the brain most often affected by hemorrhages.

By tilting the sensor, an image of the entire ventricular system can be obtained.

An echogenic vascular plexus can be visualized within the vestibule and temporal horns.

Frontal section

Multiple slices at different angles, individual for each patient, are required to visualize the ventricular system and adjacent brain structures. Use the optimal scanning angle to examine each specific area of the brain.

Axial section

First, it is necessary to obtain an image of the cerebral peduncles in the form of structures resembling the shape of a heart, as well as an image of pulsating structures - the vessels of the circle of Willis, using the lowest sections.

The next sections, slightly higher, will show the thalamus and the centrally located structure of the falx cerebri.

The highest (upper) slices will give an image of the walls of the lateral ventricles. In these slices, the ventricles and the corresponding hemispheres of the brain can be measured.

The ratio of the ventricular diameter to the hemisphere diameter should be no more than 1:3. If this ratio is greater, hydrocephalus may be present.